ID:IOTS - Infectious Disease Insight Of Two Specialists
Join Callum and Jame, two infectious diseases doctors, as they discuss everything you need to know to diagnose and treat infections. Aimed at doctors and clinical staff working in the UK.
Episode notes here: https://t.ly/8DyqW
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ID:IOTS - Infectious Disease Insight Of Two Specialists
36. Urinalysis paralysis
Join Jame and Callum as they take a deep dive into urinalysis, a commonly (mis)used test for UTI (and other conditions). This test put you into murky waters when used clinically and we hope to give some information to avoid being a pisse prophet.
Some sources referred to in this episode:
NICE Clinical knowledge summary
SMI 41: Investigation of urine
Summary article of PPV and NPV for urinalysis:
- Diagnosis and treatment of urinary tract infections across age groups, AJOG, 2018
Performance of LE and Nitrite at differing levels of bacteruria:
- Evaluation of Leukocyte Esterase and Nitrite urine dipstick, J Clin microbiol, 1999
Review of urinalysis diagnostic utility by presenting symptoms:
- Does this woman have an acute uncomplicated urinary tract infection? JAMA 2002
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Hi everyone, welcome to the Idiots podcast. That's infectious disease insight of two specialists. I'm James, that's Callum, and we're going to tell you everything you need to know about infectious disease. Soon may the editing come to discontinue the taser sun. One day, when the seer piece done, will take our leave and go. Callum, how are you doing? I'm doing fine.
Speaker 2:I heard that you'd had a bit of problem with your car because you've been on holiday and you've been driving an automatic and it's a manual car and you might see a stick shift if you were in the US and you've got a lot of North American listeners. So I think we should start using some North American terminology more. So, yeah, it came back to driving stick and yeah, it's just got you a bit down, I guess, having to go back to driving stick. You're in a dip the stick, you're in dip stick Anyway.
Speaker 1:Well, I think if that's the pun that you're going to try and release, then you're in trouble. I think it's time that you stop taking the piss at the beginning of these presentations.
Speaker 2:Maybe we should.
Speaker 1:You should stop bladdering on at the beginning of these.
Speaker 2:We should take a leaf out of Sarah's book and just go and do a culture part of the episode, because that is the gold standard for podcasts.
Speaker 1:A cultured part of the episode Interesting.
Speaker 2:So what we're talking about, as you might have guessed in the title of the podcast episode or not, because I don't actually know what the title is going to be yet, so maybe it's oh, don't take the piss, don't take the piss. We're talking about your analysis, yeah, or the urine dip stick. I don't know if that is a universal term.
Speaker 1:I think urine dip might be I'm not sure urine dip stick, but I think people will know. When you mean your analysis strips, they might vary by country, I don't know exactly. But yeah, we're going to be talking about those testing strips that people use to diagnose urinary tract infections, or at least that's what they think they're doing. So, Callum, tell me what. How would you diagnose a UTI in a patient?
Speaker 2:Well, I would use a Symptoms almost got me there. So you diagnose it as with many infections, or clinical phenomenon. And anyway, the most important part is taking a good history and you can see and I'll reference this in the show notes. But if you look at various populations, cohort studies where they took patients and asked them their symptoms and then followed that through to a urine culture and got a gold standard diagnosis that the main symptoms that were predictive of people having a UTI or negatively predictive so they had a lower likelihood ratio If they didn't have them was dysuria, urinary frequency so having those would increase your likelihood of living at a UTI and also urinary urgency and things like vaginal discharge were negatively associated with having UTI. So if you had those symptoms you're less likely to have a UTI. So that's from Geisen et al. And actually if you look at the combination Geisen et al, there we go we can't even agree on the name for our investigations.
Speaker 2:And another study bent it out in 2002, they looked at patients. If you had a combination of dysuria and urinary frequency and no vaginal discharge, this is moving. Again, you had a positive likelihood ratio of 24.6. So essentially what that means is you're a large increase in the likelihood of you having a UTI with those symptoms. You work out a likelihood ratio. A positive one is sensitivity over one minus specificity. So it's a quick way of combining those two factors. So really that's huge. So the end of the most patients with a UTI, and it's straightforward they come in, they've got dysuria, they've got urinary frequency. It doesn't look like something else, it looks like UTI, smells like a UTI maybe, and it tastes like you. Now I'm going to say that. So we don't taste urine anymore and you give them antibiotic space in your guidelines, or, if it's more complicated, then you might take some more tests.
Speaker 1:So just the loyalist knows the sensitivity of the various symptoms that Cal mentioned are.
Speaker 1:Top of the line is urinary frequency at 88%, in dysuria at 80%. In the middle is stuff like nocturia and urgency, which are about 60% to 65%, and then way at the bottom is hematuria with sensitivity of 25% and vaginal discharge with 15%. If you don't have it, you're more likely to have it than if you did have it. Exactly, and this is what the Bentatal study did they mixed dysuria and frequency with absence of vaginal discharge and got a likelihood ratio of 24, which is very impressive, and then the reverse of that had a likelihood ratio of 0.3. So if a likelihood ratio is less than one, it's the presence of that constellation of symptoms or diagnostic test is making it less likely that you've got the disease. So that's all to the good. Those are the symptoms that we look for of it. But I imagine that quite a lot of people, if you ask that question, would have said I'll do your analysis and check for what sells and nitrites. So I think it's first worth going in now and talking about dipsticks.
Speaker 2:Now, where did this come from? What's the history of urine? So there's a long history of human interest in health because it's very important. So if you look back to very ancient times, you could see that urine that was sweeter might attract insects, so honey urine, so potentially a sign of diabetes. And in Hippocrates it always pops up 400 BC, looking at color. Your order changes. And throughout history since then there's been various advancements through hundreds of years where people have looked for different things in urine and associated them with different diseases. And the main reason we're mentioning history is not because it's particularly relevant to your learning, but just because there was some, let's just say, quacks Is that the right term, I'm not sure People that were trying to take advantage of this fascination of urine, and there was a Euroscopist in the Middle Ages who decided that they could diagnose all sorts of things, from health to disease, to the future, from urine, and so they were labeled as piss prophets, which I think is just such a great name. I love that. I love that.
Speaker 1:I think we should bring it back.
Speaker 2:So, yes, piss prophets. So we're not proposing that the urinalysis is going to prophesize your future or that of your patient even. But the main test that you're looking for when you're really thinking about UTI and urinalysis is leukocyte, esterase and nitrates.
Speaker 1:So what else is on the urinalysis?
Speaker 2:Yeah, so it depends on which manufacturers one using. Sometimes they have different tests the ones that we use in the UK, the Siemens ones, and they've got other things like protein and blood which can be useful for picking up chlamydia, oenophritis, and we've also got ketones, used for diabetes, sugar, glucose, bilirubin, specific gravity, which everyone looks at and wonders what it is, and pH, which can be useful, but for the purposes of infection. We're thinking about leukocyte esterase, or leukocytes or white cell count, as I sometimes refer to, and nitrites, but nitrates. And essentially, if you're not familiar with this test, you it's very easy. You get a clean catch urine or some urine sample that you've collected and you put it into a little bottle, you put your dipstick in and then you wait the allotted amount of time. So in this one, two minutes for leukocytes and 60 seconds for nitrites, and then it gives you a color change and you read that against a scale. So it's not, it's not, it's like a semi quantitative. You know you're not got a natural measurement.
Speaker 1:But I mean, I guess it gives you a steer, I suppose, from our point of view, if you know, that's all. All those things are for diagnosing different things, you know, like diabetic ketostosis and dehydration and the presence of blood and proteins particularly important in nephrology. But what we are interested in is the top two sort of things, which are nitrites and leukocytes. Why don't you take us through what they are looking for next?
Speaker 2:Just a slight sidebar here in terms of sometimes you get called about a patient and then the story is that the urinalysis is positive. And I think this happens more like if you're say, you're on a ward, a medical board or something, and one of the nursing staff comes to you and says this patient, I think they've got a UTI. And then you wonder, you know, ask why? Oh, they smell urine. So I did the urinalysis, which is always a bit like okay, why did you do your urinalysis? And it was positive, so they've got UTI. And then you're like okay, what did the urinalysis show? Oh, garden protein. And you're like what about leukocytes and nitrites? No, Well, okay.
Speaker 1:But you sent it away anyway.
Speaker 2:I sent the sample away, and then the urine culture comes back and you've got an E coli on a urine sample and all to the patient, and then you're like well, I didn't ask for this. Why has this come to me? It's not for us to choose.
Speaker 1:Well, why do bad things happen to good people, cal? That's what I want to know. Terrible, I mean. I guess that that's a good point, because when people say the dipstick is positive, I think a good follow up for any F1s or junior medical staff that I happen to be listening is positive. For what? Because not only are we about to absolutely reign on the parade of urinalysis in general, but we're about to say that leukocytes and nitrites don't have a role in a bunch of situations, and sometimes they're not the things that are positive. Sometimes there's other stuff that's basically got nothing to do with the presence or absence of infection, which is really what we are focusing on here.
Speaker 2:So let's talk a little bit about what the tests are.
Speaker 1:Yeah, so tell me about leukocyte esterase as well. What's that? What's that for?
Speaker 2:I'll tell you about a little test I like to call leukocyte esterase. This is a test which, essentially, you've got your leukocytes and you're not meant to have white blood cells in your urine, or at least not at detectable levels. So greater than 10 cells per microliter is the sort of cutoff limit, that's in terms of how many white cells per urine.
Speaker 2:And that indicates back to urea or urinary tract infection or some other cause of inflammation in the urinary tract. So it's important to note that this is a sensitive test and it's quite specific. But there are other reasons to have leukocyte esterase in the urine.
Speaker 1:Yeah, and they would be classed as a sterile piurea, which, somewhat frustratingly, also includes TB, which is not, which is a bacterium, but tends not to culture very well, and there's therefore sometimes misidentified esterile. I'm not going to talk about them today. So what's the esterase coming from?
Speaker 2:Yeah, so it's an enzyme and basically the granules which are contained within a neutrophilic leukocyte, so a neutrophil. So it's released, this leukocyte esterase, into the urine and that can be detected by chemico-mines.
Speaker 1:All right. And what's the quoted sensitivity in Mandel's, that weighty tone and specificity?
Speaker 2:Mandel's quotes as being about 75 to 96 sensitive, which is quite a big range, and 94 to 98% specific. So I guess it depends on like what gold standard you're measuring against and your patient population. But so pretty good sensitivity and a pretty good specificity.
Speaker 1:Yeah. So since sensitivity is the proportion as a percentage of your population that have the disease, that would test positive on the test. So no test is 100% accurate. So you have 100 people that have a heart attack say randomly, If you've got a very sensitive test, then say more than 90 to 95% of people will test positive for this. And that's what the high sensitivity of troponin is. It's sensitive at detecting MI.
Speaker 1:Specificity is the opposite of that In your population, people that don't have the disease, how many of them would test negative? And so the troponin here can be used as an example too, because although it is very sensitive, it's not very specific. It goes up in lots of things. If you run a marathon, it will go up. If you have myocarditis it will go up. If you have enocarditis it will go up. If you have sepsis it will go up. So there's lots of people in the don't have an MI population that will have a raised troponin for other reasons, and so the specificities are about 70 to 80%. And so that's sensitivity is disease positive that tests positive, and specificity is disease negative, that would also test negative.
Speaker 2:Yeah, that's a proportion of sensitivity is true positive over your true positives and false negatives. And specificities are true negatives over your true negatives plus false positives.
Speaker 1:Okay, so what about nitrites then?
Speaker 2:Yeah, so nitrites are another one that's quite useful for diagnosing infection. It basically nitrate, which is a waste product, including the urine, is reduced to nitrite by bacteria which produce an enzyme called nitrate reductase. So that makes sense. It reduces nitrates. It's called nitrate reductase. It makes sense.
Speaker 1:And is it all the entrobacterial is, or is it some other group?
Speaker 2:So the enzyme is mostly commonly produced by general of the entrobacterial is our families of the entrobacterial is, if that makes sense, so things like entrobacter E coli, such a batch of proteas, CLABSALA, and you can have false negatives. So it's not as sensitive as look site estuaries. But it's more specific. So if you find nitrites, there's not much else that's going to cause that other in bacteria.
Speaker 1:Yeah, I get it. So if you find cells of bacteria, it will remain negative and maybe you'll get white cells.
Speaker 2:But in the absence of nitrites, so the batch, say the batch of your kind of like 10 to the two or 10 to the three, colony form units per mil. I think the guidance is, if anything's, 10 to the five, so greater than 100,000 per mil in the urine sample, that's like a large numbers. It's definitely ETI.
Speaker 1:Yeah.
Speaker 2:And things of 10 to the three to 10 to the five is sort of mid range like not particularly sure. The main thing to be aware about for nitrite as a test is that there are some organisms that do not reduce nitrate to the right nitrite, and the main thing is intraococcus ficalis.
Speaker 1:Yeah, so intra-cochi staph odious your grand positives. Don't do it, is that right?
Speaker 2:I don't know if it's all the grand positives, but certainly not at intra-cocus ficalis, yeah yeah. So it's very specific. If it's negative it doesn't necessarily mean that it is a UTI. And so if we come on to this, we've got a reference for this as well, but it's quite an old paper from 1999, but they basically looked at 400, just under 500 patients, women that had a suspected uncomplicated UTI, and then they got their urine cultures and classified them by having, like, how strongly positive the urine culture was, so ranging from 10 to the free calling for our units per mil, to 10 to the five.
Speaker 2:And they looked at the sensitivity, specificity of leukocyte estuaries, nitrites and then the two of them combined and also the positive predictive value and the negative predictive value of these two tests. And essentially, as you might expect, leukocyte estuaries was more sensitive and was picking up, was positive essentially, even with the tend of the freeze, the lower levels of bacteria, whereas nitrites was often not picking that up. So it was more sensitive. And if you combine the two of them so say you took leukocyte estuaries and nitrites and you had colony counts of 10 to the 5, so a good going, proper UTI. It was 84% sensitive and the two of them combined, specificity was 98.3%.
Speaker 1:Yeah, whereas in isolation, for that same concentration, 10 to the 5, the sensitivity of leukocyte estuaries was the same as the combination, but for nitrites it was only 44%, and the reverse was true for specificity the leukocyte estuaries was only 60%, but nitrites was 96%. So combining the two, you get the strengths of both, but like none of the deficiencies.
Speaker 2:So that's the higher colony counts, with the slightly lower colony counts of 10 to the 4,. What they found was that leukocyte estuaries on its own had a sensitivity of 76%, whereas if you combine it with nitrites because nitrites don't pick up UTIs at lower culture levels your sensitivity went down to 25%. So you were missing more by having that bar set to help both of them.
Speaker 1:Yeah, because the combination you have to have, both positive and nitrites, are not going to be positive at really low levels, so they're less likely to be.
Speaker 2:So my takeaway from that is that if you've got leukocyte estuaries positive, you could be a UTI, and it's not the best rule in test, because there's other reasons for that.
Speaker 2:If you've got leukocyte estuaries and nitrites positive, I'm thinking it's more likely to be a UTI now because the specificity is useful. To put that into words in terms of the data, the nice guidelines are quite clear. For women that have mild symptoms, not catheterized, we'll come to that in a second dipstick the urine and they say if both dipstick tests are negative, uti unlikely, makes sense. If leukocyte estuaries is positive alone, uti is moderately likely. If the nitrite test is positive, with or without positive leukocyte estuaries, a UTI is highly likely because it's so specific.
Speaker 2:I don't think you often see that. I think you usually see the leukocyte estuaries being positive, but putting more weight on nitrite as that sort of rule in test and for women who have a moderate or severe symptoms, with or without a catheter, make a working diagnosis of UTI without doing a deuronosis. So you're only really using the urinosis for women with mild symptoms of UTI and in men it just says don't use urine dipstick test.
Speaker 1:Yeah, but how many men and people with catheters in, for that matter have you seen urinalcies being performed on? There must have been thousands in your shorts and, some would argue, glodious career.
Speaker 2:It's a reflex thing. You're in sample but you're in dipstick in it and the problem is that you're in place weight. So, in terms of your clinical reasoning, as a methodology for examin' how we think as clinicians, which is really interesting when you I think it's easy to on paper say objectively, like this, what influenced my decision making, just like the free drug rep lunch won't affect my prescribing.
Speaker 2:So, you know you can look on paper and say like, actually you know we'll come onto this in a little bit about like positive and negative predictive values of tests and say, ok, well, I know that it's 50-50, so it's actually influenced my decision making. But if you get a test on a piece of paper and it's got a very clear result, it's quite hard not to be influenced by that.
Speaker 1:It is yeah.
Speaker 2:Even if you know that the test should never have been done or is nonsense. So like, for example, you know, when you get elderly patients, particularly women, and they've had a urine sample sent because it was positive on a urinalysis and it turns out that of an E coli and culture, I think a lot of people struggle to say, like you know, we as a lab have said here's a urine sample that's positive for this organism.
Speaker 2:And they end up getting antibiotics even though people are like, well, they're not any symptoms, it's probably asymptomatic bacteria. But then suddenly you're doubting, like, or they just maybe not mentioned symptoms, or they're mildly confused, maybe that's because of the ETI.
Speaker 1:I mean, it's hard to ignore it if you have somebody who couldn't tell you if they've got those symptoms that we've mentioned previously.
Speaker 2:I think even people do tell it. I think that this happens a lot is that we do your analysis and it's positive for people get antibiotics even though they don't have symptoms or they have a culture back.
Speaker 1:I mean there's. There was a case in on my I'm on consult service at the moment and there was a case where I was reading through the patient's notes and one of the other red registrars junior registrars had advised giving a course of an antibiotic for a person who was catheterized and didn't have symptoms. But they took a sample and it showed a clebsiella. And the listener may be wondering why do we care so much if they're getting just a short course of 94 Antone or trimethybrom? Well, what if they're not? What if the clebsiella that comes back because XDR? That's happened to me a couple of times and I was agonizing over what to treat them with and then I went and asked the team and then asked the patient like wait a second, do you have any symptoms because of this? Let's see. Well then it's just a symptomatic bacteria and you know, if you want to treat this, you'll need to change the catheter and we'll need to use a carbapenem or we should do a full episode on catheter associated TIs, because I don't think we should.
Speaker 2:Yeah, it's not easy.
Speaker 1:But like, do you know what I mean? Like, once you've got that information, the temptation is to act on it. Yeah, and this is true for lots of diagnostic tests as well, and it's especially true for your analysis. So you're encultured in the line.
Speaker 2:So there is a niche, that there's a small group of patients in which we your analysis is useful, and that's essentially women that are less than 65, that present with mild symptoms and you're not entirely certain it was the UTR or not, and it can be helpful for pretty much every and also for non-infective reasons, is worth mentioning. So if you you're suspecting some sort of renal disease, but in the context of diagnosing an infection there's not many other circumstances, you should never your your analysis a catheter specimen, because basically you've got plastic in your urinary tract, you're going to have a positive leukocyte estuaries and there's probably going to be bacteria there and those bacteria will have nitrate reductase, so nitrates will probably be positive as well. Nothing about whether the patient has a UTI or not. So don't never send you know, never base any decision on that and just don't do it. And it happens again and again and again and again. So as a plea, please, please, don't you're in dip catheter specimens of urine.
Speaker 1:Yeah.
Speaker 2:Also in men, because it's more unusual to get a UTI if the patient's got symptoms. Even if you're trying your analysis as negative, it's not going to your negative predictive values not going to be that good. So actually it's not worth doing because it's not going to change your decision making.
Speaker 1:Yeah, so nice recommend this, and so can you. Can you walk me through the justification for that?
Speaker 2:They basically just say don't rely on your dipstick or your analysis test to confirm the dinosaur UTI. If they've got milder, non specific symptoms, UTI not capitalised. A negative urine dipstick to both nitrate and leukocyte estuaries means that UTI is unlikely, so it may be helpful.
Speaker 1:Yeah, but only in mild or non specific symptoms. Yeah, yeah.
Speaker 2:So basically, if you already think they probably don't have a UTI, like they just got a bit of not to your ear or something, it's probably prosthetic symptoms you know they've got BPH or something, and then you're doing a urinalysis just to just reassure yourself, essentially. But if they've got you know, good going symptoms of UTI, then you're not going to rely on a negative urinalysis, you're going to get urine culture. True enough, like yeah. And the other group is don't you know, an elderly patient? So particularly women over 65 is the sort of in the guidelines, though maybe 65 is too young. Now there's a high rate of asymptomatic bacteria and urinalysis can't really tell you the difference between asymptomatic bacteria or bacteria. So you know, sending urinalysis in that situation is not helpful either.
Speaker 1:Yeah, yeah.
Speaker 2:So you've come, you've got patients who present to your GP surgery general practitioners and they're young women and they've got a possible UTI. Okay, and at this point we're thinking that before any tests, before any history, before doing anything, there's maybe a 50 50 chance of that patient having a UTI. I have a draw, come into a second Now. If they have the symptoms we talked about earlier on they've got frequent urinary frequency and dysuria, they're pre test probability. So how likely they are to have a UTI before doing anything else has gone up to 73% already. And if they don't have vaginal discharge, that's up to 90%. So before doing the urinalysis is 90% chance this patient's got UTI.
Speaker 2:We can then do the urinalysis. If they've got a positive nitrate or plus or minus Lucas esterase, we're looking at 97% post test probability. So in that situation where you think they probably got UTI, you're already 90%. You do the urinalysis is positive, bang, you're 97%. They've almost certainly got UTI. But if you've done the urinalysis and not that group and they're negative for nitrates and Lucas esterase, they're still more likely than not to have a UTI. You know they might have a low level of bacteria in the urine. So it's still 71% of patients in that group with negative urinalysis. But they have the really strongly suggested symptoms. They're still more likely to have a UTI. So you're still going to think I'll give them some antibiotics in the urine culture. So is that actually that useful?
Speaker 2:And then the other line of the end of the spectrum, I guess, is a patient that comes in and they don't have urinary frequency and they don't have any dysuria Before you do any tests. Their pre test probability is sitting down at 23%. And if they've got vaginal discharge then you're down to only 8% of those people have a UTI. So it's much more likely they've got an STI at that point, even if you have a positive nitrite plus or minus. Look at the site esterase. In that group your post test probabilities only 27%. So one in three people essentially might have a UTI.
Speaker 2:So it's still more likely not, they don't have a UTI. And also because essentially you've got an STI that can give you a positive look at the esterase and other tests. So is it that useful there either? And then basically what you want is a test that's going to say yes or no, is it a UTI or not? And you can talk about having a good sensitivity and specificity. But really what's in my head important is probabilities and these are like in the lab, in like a gold standard setting in a research paper you can say is a very sensitive test and it's very specific. But when you have patients and you put into the mix like the actual history and the situation you're in, right there you really have so much information that your analysis rarely is going to say definitely yes or definitely no, you're often just left thinking, well, it could still be or it might not be.
Speaker 2:It's maybe like an extra tool in your armamentarium of things that are supportive evidence and things that are not supportive evidence. But then I think the issue of that is that we, as clinicians, are prone to putting more weight onto things that are seen as objective than things that are seen as subjective. Even though actually symptoms and a lesser extent signs are much more useful in most situations and it's not an expensive test, you know. That's fair to say. Compared to a lot of the other things that we do, it's not expensive.
Speaker 1:No, I mean it's. Running a urine culture is much more expensive than a dipstick Got 20 pound. Yeah, that varies from different bits of the country and if you've got something called a Kestra, which BD will sell you for a pretty penny, you can run your urines for less about a third less than than sort of standard urine culture.
Speaker 1:It's a big automated lab robots and yeah, but lots of conveyor belts is very cool. You know, like just because it's cheap doesn't mean it's good, and just because it's cheap doesn't mean you should use it on everyone. So if you think about anyone with a catheter all men and all women over the age of 65, your group that you should only be using in is already un-cathed drives women with mild to moderate symptoms under the age of 65. That's like not a lot of people. Most of our patients are older than 65.
Speaker 2:That's maybe our bias, because we're hospital hospitalists, I'm going to say like that so in the community, the vast majority of people that are affected by it and that's not true, but a lot of people will present in that group. But the thing is, most of those patients will have uncomplicated UTI and you're not meant to do your analysis then anyway, you just get them antibiotics into them underway, or actually, but will they resolve without antibiotics?
Speaker 1:Yeah, or give them an anti-inflammatory and wait a few days for a urine culture result and then find out actually what the hell you're doing.
Speaker 2:So we've talked about your analysis and I think that's pretty much all we have to say about it. We'll come back and we'll talk more. There's a lot to say about urine-eutecton infections, about diagnostics, urinary culture, et cetera, and also treatment. When do we use your analysis? What sort of takeaway from this, James? How do you become a responsible urine dipper and not be a misprofit?
Speaker 1:I'm not too sure, when I would really want the results of your analysis. To be perfectly honest with you, maybe I'm not the best person to ask. I already wasn't all that keen of them before the start of the podcast and nothing you've presented has made me favour them more. So you better tell me when you want to use them.
Speaker 2:Yeah, it's difficult. I think we're kind of in that luxury position of being in a hospital. You get access to a lot of tests and a lot of information and you try and wake up in an objective sense and it is quite nice to when you've got someone with you know. I guess what I would say is it's easier to say when you don't want it, isn't it? Like those groups of patients that we've already said it's not useful and don't do your analysis on them? That should be a takeaway message Don't urinate, alice. Like after specimen urine.
Speaker 2:And in patients where it's really clear, like they've got barn door symptoms, you know there's pus coming, you know, like who knows what it is, but it's like barn door UTI, it's very clear. It's not useful there because even if it's negative, still thing hits UTI. And in patients where it's like you're really not thinking it's a UTI, again it's not really useful. I think it's probably of some benefit where, like maybe they've got one symptom, like they go about dysuria frequency, you're not particularly certain and you're really on the fence about whether or not to give them treatment or send a urine culture. I think a positive urinalysis in that situation might just push me slightly towards the side of saying this maybe is a UTI, but if you look at the percentages it's still not certain.
Speaker 2:So it's not going to give you a definitive answer and it's not something to be relied upon. It's just an extra little bit of you know. It's the cherry on top of the diagnosis of UTI. It's not really the meat. The meat, the flesh no, that's not the right term the meat of the pudding. I'm looking for analogy here and I can't quite hold on to the phrase cheese of the cheesecake. I think I'm hungry. I'm making food analogies.
Speaker 1:Do you know what I mean? It's not the crunch, it's not the most important thing by a long shot. No, and there's plenty of other things you can do, like shock horror on an infectious disease podcast. I actually get a history from a patient. I would heartily recommend that and that will tell you most of the information that you need to make the diagnosis. I suppose the issue, cal, is what if the patient can't tell you? You know, old man comes in confused, off legs, not knowing why. Chest X-ray there's maybe a bit of fluid on the bases. You don't know if it's infection. You don't know if it's not. There's no cellulitis. Abdomen's okay. Do they have a UTI? Do they have a chest infection? Why don't I just cover both? Do you know that kind of case? Yeah, we've had hundreds of cases like that and do you know? Do you think the UTI? Your analysis got any utility there or do you gain? Do you just think because it's male?
Speaker 1:Well, if you look at. So there's a couple of studies. You can meet the patient female, can't you?
Speaker 2:There's a summary article clinical UTI across age groups in the Journal of Neutrism and Gynecology 2018,.
Speaker 2:And they looked specifically for the older population. So D'Chamal, d'villetal and D'Fanny Metaal I'm definitely saying them all wrong and they looked at nitrite plus or minus lucasite estuaries or most of them did anyway in the older population, and they quoted a sense of sensitivity and specificity. I don't really interested in that. So the positive predictive value if you had nitrite plus or minus lucasite estuaries is about 45%. So if you took 100 patients that you thought might have a UTI and they were positive for nitrite plus or minus leukocyte esterase, only 31 to 45% of those actually likely to have a UTI and the negative predictive value is better, so it was 92 to 100%. So I guess the use case there is if you're thinking I'm not sure what's wrong with this patient and you do your analysis and it's positive, that does not mean they have a UTI and I think that's what is usually interpreted as yeah, but actually, particularly in older patients, often it's going to be something else or they've got asymptomatic bacteria.
Speaker 1:But I guess it's like the D-dimer, isn't it? The negative predictive value is what you're after, because if it's negative, then they almost definitely don't have a clot, and if it's positive they could have anything. It could be a clot, it could be infection, it could be this, it could be that.
Speaker 2:Yeah, it's not going to rule all of them, but it does definitely make it less likely.
Speaker 1:I mean, over 90% is pretty good for most tests, cal. Yeah, that's true, I'm perfectionist, jim.
Speaker 2:So you are. So, yeah, maybe we've not made that entirely clear, and I think that's because it's such a widely used test and it's so easy. Like, if this is a £100 test, right, I think it'd be very easy to say just don't use it, just chuck it in a bit.
Speaker 1:Well, I don't think. If I may wax on wax poetic for a bit, I don't think the issue is the cost. The issue is the consequences of acting on the results when they are misinterpreted. Oh, that's true. Do you know what I mean? Like? The issue is what if the guy doesn't have a UTI that's causing them problems, but you dip it, or the nurse dips it, and they find white cells and blah, blah, blah and they say, oh well, I'm going to send it away. And it comes back and you've got a culture result. And what do you do with that? Do you treat it? You're obviously more likely to treat it now than if you didn't have the results sitting in front of you. And even if it's a plain bog, standard UTI and you can treat it with normal antibiotics, forget multiple resistances. Like I said before, that is increasing the antibiotic burden. That is driving antimicrobial resistance. That is not a good thing.
Speaker 2:Yeah, yeah, from a stewardship perspective, your analysis are not great. So yeah, there was a campaign, wasn't there? It don't be a dipstick.
Speaker 1:Well, there's the Choose Wisely campaign in the US, which is all about diagnostic stewardship choosing not to do tests because of this risk of overdiagnostics. It's not just related to infectious diseases, like an emergency medicine sort of driven thing, but one of them, I'm pretty sure, was not doing dipsticks in people that don't have symptoms of it and that's the thing. If you just confine yourself to not doing them in people that don't have urinary tract symptoms already, you would have eliminated at least half of all the urinalysis that are performed in the NHS.
Speaker 1:Yeah that's true, and eventually there would be a cost saving associated with it, if not a cost saving of the urinalysis dipsticks themselves, because they are inexpensive, but it does take staff time to run them, that's true.
Speaker 2:And also the decision time of having to pour over the soap and be like what do I do with this?
Speaker 1:And the drug burden of the treatments that you then put them on and the prolonged inpatient stay, blah, blah, blah, and the antimicrobial resistance down the line, which is like a year's down the line effect. But there are consequences to doing this that you can avoid by just not doing the test or realizing how bad the test is in the first place. We spent a lot of this episode basically just crapping all over urinalysis. We're going to do a UTI episode shortly and we'll mention urinalysis there, but most of our chat will be about urinary culture, because that's probably the main thing that we use and that's not for diagnosis, that's for finding out what the bug is so that we can treat it, because you diagnose it on the symptoms.
Speaker 2:That's a lovely sentence to end on James.
Speaker 1:All right, and so we shall. Questions, comments, suggestions. Why don't you send them into Idiots Podcasting at gmailcom? Have a five-star review in your pocket. We would love to have it. Why don't you drop it into your podcast player of choice? We tweet at idiots underscore pod and if you want to buy us coffee, you may now do so. There's a link in the podcast show notes. And until next time, I'm James, I'm Kallen. See you there. Now that the episode's done, we hope you learn and had lots of fun. So go forth and treat people with some of what you now know.
Speaker 2:That was just like the best rundown of all the stuff that we have to say that you've ever done, so I just want to say well done. Oh, thanks, man, I should listen back to this and then write it down so that I can see it at the end of every episode, you know there's actually this wonderful technology that we're using, where I could just copy that very tidbit there and then put it into the next episodes, like we do with the music.
Speaker 1:But part of me thinks I would kill the joy, I know, but like I could do the intro as well, like you could do it with the intro, too I could.
Speaker 2:It would save you so many words. But I think for me part of the real fun of this is, each week, me slightly panicking, trying to think about how to say the Twitter handle.
Speaker 1:Where we're still recording, we're still recording.
Speaker 2:I think all right stop recording Is the real high quality, professional approach that people come to our podcast for.
Speaker 1:That's what we're doing and possibly Bye.
Speaker 2:Thank you for watching, guys.
