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Hello and welcome to this St Emlyn's podcast. I'm Iain Beardsell and I'm Simon Carley. What we're going to try and talk a little bit about today is the core of emergency medicine work. What patients come to us asking? They come to us and ask, "Doctor, what's wrong with me?" And we endeavour through a series of history examination and tests to find the answer for them, to tell them what's wrong. We just want to have a little bit of a chat about what that really means, what it
means to make a diagnosis. Simon, to you, what does it mean when you're actually diagnosing a patient and you say to them, "You have this condition?" Well in day-to-day practice, what I'm doing is I'm applying a label to them. So I'm saying either you have this condition and that I'm going to do something on the basis of that or more commonly in emergency medicine, we're saying that you don't have something because we're rule out physicians and it allows somebody to go home.
So I'm saying things like, "You don't have a my-carlin function, I'm fairly confident this isn't chest pain due to cardiac disease, you can go home." So we're using as a label to make decisions. That's how we do it in day-to-day practice. And it's probably worth just thinking a little bit more about that. So we tend, I think, to work backwards. We don't start off with trying to say what's wrong with a patient, we tend to start with saying,
"We're going to take the serious stuff and rule that out." And work backwards if you like. Is that a reasonable way for us to work? Yeah, I think so because we're most interested in things that are going to kill you and in particular things that are going to kill you quite quickly and in the UK certainly things that are going to kill you within four hours. So we're really interested in spotting those at an early stage so we can do something about it. So we are a bit backwards.
It means that we're very interested in diagnostic tests which tell us what people don't have. So we're looking at tests which we would describe as very sensitive that we'll pick up anybody who has the condition. And those tests, I guess, don't just need to be blood tests, but anytime we ask a question or perform part of a clinical examination, these are all parts of our testing strategy. So asking a patient about their clinical
presentation, we're always doing tests, aren't we? It's just not necessarily that they're what we might regard as tests in the blood test kind of idea. Absolutely, and that's really important because people think about sensitivity specificity of this blood test or this x-ray, but everything we do, absolutely right, so important. And the most powerful tests that we have are clinical history examination. So, you know, a sensitive test for
have you had a cardiac event is, do you have chest pain? And a really specific test would be something like temporal to rightus? Do you have jaw claw education? So there are questions that we can simply ask patients or examine them about, far more powerful than a serum rhubarb that you might get back from the lab in two hours. So in all of this discussion, we've got to put inside of that that our key work is done in the history and then in the
examination to a certain extent, but it's all about the history. And maybe if we start thinking of our questions within the history as diagnostic tests, that's going to help us get to where we need to be. So we're going to think a little bit about how we tell a patient they don't have a certain illness, how they don't have that diagnosis. And we start with the life threatening stuff, I guess. So how certain do you think we have to be
to say that a patient doesn't have one of these life threatening illnesses? The ones that we all worry about, the SHO is a dead panic about in their first few weeks, the MI's, the misPE, the aortic dissection, the subarachnid hemorrhages, everything that keeps us awake at night. How sure can we be? Are we ever 100% sure that patients don't have those? Oh, it's really interesting, isn't it? If you go out and ask people, they think they are, but they're not. And so we let's explore that. So how
certain do you need to have to be? Well, if you are thinking about sending a patient home or about not doing something, so you can declare them as not having the condition. What does that mean? To me, it means that you're identifying a group of patients who are highly unlikely to actually have the condition. Yeah. And secondly, that if they do have the condition, it's either a very low level of it, so it's a very minor type of a very low grade event.
Thirdly, that if they do have a complication, it's unlikely to be very sudden, very precipitous and very serious. So at the extreme end, I think you mentioned subarachnid hemorrhage. If you miss a subarachnid hemorrhage, it could be a sudden dramatic deterioration very quickly, and you might not be able to get somebody back from that. So that's a very, very important thing to spot. There be other things which wouldn't be so important to spot first time around.
So something like a small flake of ulcine fracture of a lateral maliolus, does it really matter that much if we if we miss it? So we can tolerate different levels of certainty depending on the clinical condition we're looking for. So if we take some of those life threatening conditions we've talked about, the ones that we really worry about. Let's use pulmonary embolus because that's always
talked about the diagnostic testing and other things. How sure do you need to be that a patient who's presented with short and subreth and/or chest pain hasn't got a pulmonary embolus before you can say, "I can stop testing you now." Or "I can stop asking your questions or I can stop what I'm doing." And you can move on to ruling out the next diagnosis on the list of problematic things. Where do we have to be with that? Because from what I think we're saying is you're never 100% sure.
No, and we can put some numbers on that later if you want, but the important point is you're never completely sure because most of the tests that we would use, we talk about some certain tests being very sensitive. And there's a ballpark figure which is knocked around and it's kind of culture and practice as much as anything else. But if you've got a test that's more than 95% sensitive or certainly 98% sensitive for serious conditions, that's a pretty good test.
And mathematically it is. If I sold you that something picks up 98% of something, it sounds good, doesn't it? Yeah, that's a 98% if I'd got that in my exams, my mum would have been well-chauffed, I would have got a cookie and a glass of milk. So 98% I'm fine, thank you. Yeah, there's probably been investigation about how you got such a high marquee. But yeah, sorry about that. But 98% that means you miss one in 50. Hold your horses, I miss one in 50, now I'm not happy.
Yeah, which is why just expressing something as a natural frequency rather than as a percentage and makes people feel differently and there's loads of evidence out there, I'm not going to talk about it today, but loads of evidence that how you present data makes people feel very differently about it. But a 98% sensitivity means that you miss two out of a hundred people with a condition. So that's one in 50. And then that's a fairly accepted level of high sensitivity, but we've got to
accept that still means you miss a significant number of patients. I don't think people understand that. I think people are deluded a lot of the time, I think they believe that high sensitivity tests rule out everything completely. That's how people behave anyway. Well, I think there's a couple of things there, isn't the first expectation of our patients upon us and of ourselves is that we're never wrong. So certain publications in the UK would be absolutely delighted if we went ahead and said,
you know what, we sometimes get it wrong. But perhaps it's the language we use that makes that difficult. Are we missing cases or is this just part of being good doctors or do we have to keep investigating until the point you never missed something? Even though those investigations, I think as we'll talk about another time could end up doing harm. So we're a bit between a rock and a
hard place really, aren't we? We need to have a nice balance of where the risk is. Yeah, because I mean, one of the reasons we do use diagnostic tests in the ED, which don't have a hundred percent sensitivity, you know, an a perfect rate of peeing up everybody is that by pursuing a diagnosis, you can actually
do harm. So let's take a DVT for example, we use testing processes which have got 98% sensitivity to avoid having to do things like vanography, which is an invasive test at some pleasant is expensive, it's uncomfortable for patients. And we use diagnostic testing processes for PE to avoid having to do in the past certainly CTPAs and even pulmonary angiograms which have got a significant risk associated with them. So you reach a balance point where pursuing the diagnosis further is probably
not wise. And there's another point as well, conditions that you miss that 2% that you miss are probably and in most cases the patients who have the smallest burden of disease. So a massive PE is unlikely to be missed than a teeny tiny one and therefore the consequences of the miss aren't as great. And we actually, again we deal in absolute, don't we, you have a PE, you don't have a PE, we rarely put
a quantity on that I guess because we're not really sure what that means. But I guess massive PE, we will say this is a massive PE because it changes what you do next. But we just give them a label of disease rather than how bad that disease is, you've had a non-stemmy, we don't necessarily
say how bad that non-stemmy has been. Yeah so when you make the diagnosis so you say you've got the label are we saying you've actually got the disease or are you saying you're now in a population of patients and if we treat that population of patients which is a mix of people who actually have the disease and who don't have the disease overall your benefit. And that's how medicine
actually works. When you go through a diagnostic process and you come out the other end if you've got, if your tag positive diagnosis positive you're a mix of tree positives and false positives. And we then take that group of patients, we do trials on the MarCTs and decide whether that group of patients which is always a mix benefit or don't benefit from treatment. And similarly we look at patients who don't have the label applied and they're a mixture of people who generally don't have
disease and some misses so some false negatives. And we look at that group of patients and see if they benefit from not having had the diagnosis made. Well that's a less common study. So more and more
we're dealing in uncertainty and we're removing some of those absolutes. It's probably worth just taking a couple of minutes out if you can cover it in a couple of minutes and thinking a little bit about what we mean by sensitivity and specificity just because we're going to be talking about it a lot. So if I've understood it correctly, sensitivity, snout and spin so snout being sensitivity, that's a test that helps you rule out disease. But it's actually measuring the number of people who
test positive over the number of people who actually have the disease. Is that right? A sensitivity is basically a measure of whether or not you can pick up the disease. So what you want from a sensitive test is that it will be positive for everybody who potentially has it. Now that will be a mixture of people who actually have the disease and also some people who don't. So a test like D-Dimer
for thrombobot disease is very sensitive. It picks up lots of people who've got the disease, most people who've got the disease in fact, but also picks up a bunch of other people who haven't as well. But it's still very sensitive. But the key for us is that there's very few false negatives with a sensitive test. So because there's a few false negatives, if you get a negative test, you're reassured that that negative test is correct. Am I getting down the right line here?
Yeah, absolutely. So a negative test means that you're unlikely to have the disease. Just because that false negative rate forms part of the sensitivity equation. Yeah, sort of, but that one in 50 that we talked about before, that will be the one in 50 you will be falling into that group who actually had a negative test, but do you have the disease? Their false negative. Exactly. Absolutely. Then if we just flip that round quickly hoping that we can take specificity in amongst all this,
we've said that specificity is a rule in test. So if you've got a highly specific test, it's a rule in. And again, in my head, that means that we have few false positives. So if you get a positive test result, it's likely the patient has disease. Yeah, if the test is positive, so if you have that characteristic or you have that feature, they are very likely to have the disease. The one I always remember, and I use it in a lot of
examples is jaw claudication and temporal arthritis. So only 4% of people with temporal arthritis have jaw claudication. But everybody would be jaw claudication has temporal arthritis. So it's a very specific test, but you couldn't use it as a screening test because only 4% of people have got it. I get you. So we're going to be using these terms quite a lot, sensitivity and specificity. I think we'll probably be doing a lot of that sensitivity because that's our rule out thing
that we're thinking about more in the emergency department. So hopefully we'll come back and I think repetition is learning. So repetition is learning. So what we'll do is we'll go over those terms a bit more because if we can get those implanted in our brains and our listeners brains, then we might be getting somewhere. So where we've got to so far is that the patient comes to us and they want to
know what's wrong with them. But actually we're going to work in reverse and say well let's work out first what isn't wrong with you and work out that you haven't got these life threatening conditions. So we're working backwards. We thought a little bit about how certain we need to be and we reckon one in 52% or 98% certainty is about right? Yeah it's culture and practice but yeah that's what
most people are working to. So that may be a bit of a bombshell for some people who are listening. We have to become more accepting that we're not always right and that we may be getting we may be what we're going to call misdiagnosis even though perhaps the terminology isn't as helpful. But even if that happens the burden of disease may be so little although they have it that they come to know harm. Is that what about we are? So when we're thinking about misdiagnoses
and how important they are then you can investigate that in several different ways. The first thing is that they're probably got a slightly less severe degree of burden of disease. So for instance big Ps more like to be picked up you've got a massive pancreatitis you're more likely to spot it. If you've had a massive MI you're more like to spot it in a small MI that kind of thing. So burden disease is important so it means the consequences of your missus isn't as great. But the the other
thing about missing diseases is again how quickly it's going to come back and get you. So it's acceptable to miss certain conditions. If you know that they will gradually get worse and therefore the patients likely to come back to the hospital means you can do something about it when they come back. You know so missing things isn't a disaster. It's a natural consequence of being a good diagnostician and using
good high quality evidence in your in your diagnostic protocols. But it does mean we've got to tell the patients that. So if you tell the patient you definitely not go that got your condition don't come and darken my door again. You've definitely got an MI why you bothering me. Then that's a really bad practice because a number of them will come back. And if you told them that when they went out of the door
they're not going to be very happy. So I'm pretty comfortable with the idea that we're working through a series of tests. They might be part of the history, the examination. There might even be blood tests, radiological tests to say a patient hasn't got an illness. And when they haven't got an illness we just don't treat them obviously and we reassure them and we move on and we try and find out what
is causing the illness. If we flip that the other way around and actually perhaps work in the way that most people think we work which is to say when a patient has got a disease how sure do we need to be that a patient has an illness in order to then firstly dismiss all the other things that are on the differential but also go ahead and start giving them treatment for whatever that illness may be. Are we always sure that people have illness or disease and a positive diagnosis or is that again
uncertain? Well if you want to get really pedantic about it and those are different terms of course illness and disease are different things. So illness is what the patient experiences, diseases, the process. What the important thing is you're asking about I think is what happen it's the consequence of making a diagnosis in a positive way. So if you apply the tag to somebody
and say you have this what are the consequences of treatment? So if we take the big ease again so something like my cardinal infarction there are significant consequences to making that diagnosis. That patient is going to get thrombolysis or go to PCI and be exposed a whole bunch of different drugs which are going to potentially expose them to bleeding events and all sorts of things.
So there are risks in making a positive diagnosis and we don't always know whether they're going to benefit, whether they're going to suffer harm, whether it's going to make no difference at all. And I don't want to go there but we could think about strokes or thrombolysis here but we haven't got six hours have we? Well I'm also that the internet and phone is so a wash with strokes or
molices I'm not sure that we need to add anything to debate I guess. And so when we're making a diagnosis we have to now not just add up what it is we're saying but what the consequences of treatment for that diagnosis might be and those consequences can be very different for us in the emergency department say from in family practice or general practice. So the idea that you have an MI is very different from the idea have you got a streptococcal bacterial throat infection or a viral throat
infection the consequences are very different. So how sure do we need to be if we were to put a percentage term on it like we did before? How sure do I need to be that a patient has something in order to treat them for something? I think it entirely depends on what the consequences of your actions are. So let's take a simple example I'm very big into chest ultrasound at the moment so I'm chest ultrasounding all our major trauma patients if they've got a new mothorax on the
ultrasound when they come through and putting a chest training with our chest actually. So that's a significant consequence of that patient. Would you agree? Yeah especially if they don't have a new mothorax and your test wasn't yeah and if I'm rubbish then there's a bit of a problem that's a
significant. There's a significant consequence to it. Let's just put out there I'm not in a tall suggestion that professically I'm sure your brilliance at it but we can even take that diagnosis before the arrival at hospital when we're seeing major trauma patients who've been seen by pre-hospital providers who may or may not have access to ultrasound are trying to do a clinical examination in different difficult circumstances so we could describe their sensitivity and the
specificity of their tests be that history or examination it's all much more limited than perhaps we get in hospital these patients are then getting thorough costumies on the best available evidence in the pre-hospital environment and then in our clean brightly lit huge scanner of a hospital we find out they didn't have a new mothorax but there has been a consequence to that decision
being made and that's based on the testing that's been gone before it. Absolutely and you can apply that kind of logic to many of the things that we do so how sure you got to be definitely depends on what you're going to do about it if you make a diagnosis but actually there are no consequences from it for instance you make a diagnosis of a viral sore throat and I'm not doing anything about it there's no consequences no harm you can do it as often or as little as you like really
but when you're talking about a therapeutic event which takes place as a result of that diagnosis being made then you've got to be pretty sure and particularly if there are harms associated with it so for the biggies for us things like thrombolysis things like PCI things like going to an operation if you dissect free fluid on your ultrasound about imaging the chest about intervening in the chest about making airway interventions etc etc etc all of these big things
that we do in the ED I think you've got to be fairly sure how sure is fairly sure it's a balance and that's why we are clinicians we're not automotons we don't follow strict protocols and we have to have some judgment but that judgment is much better informed if you understand the probabilistic nature of the diagnosis that we make so with that I think you've just dropped the pebom there at the end the word probabilistic which I think is something we're going to come back to
in episode two to discover a little bit more about discuss a bit more about we've just started to scratch the surface of what it is we really do a new emergency department we aim to rule out disease those life threatening diseases but when we can't rule them out we need to have a degree of certainty about ruling them in and we need to use good diagnostic testing and also much more importantly good clinical acumen to make the decision to do the treatment and these are all topics
that we're going to discover a little bit more about in further podcasts just want to leave you to have a think about everything we've talked about reflect a little bit think about how that affects your practice and we'll be back very soon with part two discussing a bit more of how we make decisions and diagnoses in the ED hope take care again yes before we go yes what's your favorite diagnostic test my favorite diagnostic test here but you see I would say that my favorite diagnostic
test is taking a history yeah that's kind of the that's a two answer no just just at the end we could do what's your favorite diagnostic test okay let me think my favorite I'll do the check again okay I haven't got the answer yet hang on yeah let me think favorite diagnostic test that I like the most tricky go on let's just do something on the fly okay so um Ian what is your favorite diagnostic test anyway Simon I have to say I'm renowned in my department for being the
man who's anti-testing I'm always trying to reinforce to our doctors and nurses that history and examination is the key but I suppose there are times when we need tests to make decisions for us and we need to enhance our decision making capability by using technology be that blood or radiological testing I guess the piece of kit that I enjoy using the most because I can use it is the ultrasound machine and I actually like that most in the recess room I enjoy I think the
pneumothorax example is a good one it's the thing that you can do immediately you can make a an intervention and arguably that test is has better characteristics than any of the other tests we can do so I'm going to plump for ultrasound in query pneumothorax in trauma patients how about you and it's interesting you've gone cool you see you've gone for the cool test it's got nice shiny kit and then electronics and I'm with you on that and with you on that I'm going to go for D-Dimer
really but everyone hates D-Dimer and that's why I love it because D-Dimer is not a bad test it's just badly used what I love about D-Dimer is it can be incredibly valuable and incredibly helpful if you understand how diagnostic tests work so I love D-Dimer because when anybody comes up to me and says you know what I hate D-Dimer is the rubbish it gives me the opportunity to talk to them is for between 45 maybe 50 minutes on diagnostic testing and you know
what I love that and I really reckon that once this goes public no one will ask you about D-Dimer's again envisaging 45 minutes spent with you talking about that any obviously 45 minutes with you would be delightful otherwise and on that final note we look forward to speaking to you again soon on this eminence podcast enjoy your emergency medicine and take care see you soon [music] [BLANK_AUDIO]