Why not do a test for bacteria or virus at the GP clinic?

maninasia

Here's a thing that bugs me about visits to the GP. Doctors will do an examination and often make an informed guess according to the cause of a sore throat or runny nose etc. Why not do a test for flu virus or strep throat etc? There are POC tests available for these diseases now.

I think it's time doctors stepped into the 21st century and used technology to improve diagnoses instead of going on guesswork.

Discuss.

RobFowl

maninasia wrote: »

Here's a thing that bugs me about visits to the GP. Doctors will do an examination and often make an informed guess according to the cause of a sore throat or runny nose etc. Why not do a test for flu virus or strep throat etc? There are POC tests available for these diseases now.

I think it's time doctors stepped into the 21st century and used technology to improve diagnoses instead of going on guesswork.

Discuss.

2 reasons stick out

1) Identifying which bacteria/virus is the causative agent will in the majority of cases make no difference to the treatment and as such is simply a waste of time, money and resources.

2) the tests often have high false positive and false negative rates and are far too often neither sensitive or specific enough to be relied on. Throat swabs are a good example of this. Also identifying which strain of the common cold some one has is virtually pointless in clinical terms.

maninasia

So can a GP easily tell the difference between a bacterial and viral infection without assistance of a diagnostic test? The relative rate of false positive/false negative results from a test may be much lower than using physicians judgement.

At least if you ruled in/out bacteria you could prescribe antibiotics or not?

Then the flu is obviously a more serious viral illness, perhaps would be useful to know it is not a common cold? During an influenza outbreak it might be more important or for elderly patients. I guess GPs use a quick test then?

Then theres things like meningitis, any way to test for that?

tallaght01

maninasia wrote: »

So can a GP easily tell the difference between a bacterial and viral infection without assistance of a diagnostic test? The relative rate of false positive/false negative results from a test may be much lower than using physicians judgement.

At least if you ruled in/out bacteria you could prescribe antibiotics or not?

Then the flu is obviously a more serious viral illness, perhaps would be useful to know it is not a common cold? During an influenza outbreak it might be more important or for elderly patients. I guess GPs use a quick test then?

Then theres things like meningitis, any way to test for that?

Treat the patient, not the disease.

You'd need to test for about 9 viruses too. Better off just prescribing less abx.

RobFowl

maninasia wrote: »

So can a GP easily tell the difference between a bacterial and viral infection without assistance of a diagnostic test? The relative rate of false positive/false negative results from a test may be much lower than using physicians judgement.

At least if you ruled in/out bacteria you could prescribe antibiotics or not?

Then the flu is obviously a more serious viral illness, perhaps would be useful to know it is not a common cold? During an influenza outbreak it might be more important or for elderly patients. I guess GPs use a quick test then?

Then theres things like meningitis, any way to test for that?

Tests are useful in some cases but none are 100%. Not all bacterial infections need antibiotics either.

They're generally as useful adjunct if the is sufficient uncertainty but routinely testing everyone (or large numbers of patients) would definitely increase the cost of the health care system with a questionable if any benifit for the patient.

Meningitis can be notoriously difficult to diagnose and there are tests but always be aware they may read as a false positive so cannot be relied upon on their own.

Good clinical judgement from a physician after examination and history taking remains the most important aspect in diagnosing.

Sitric

It's much more useful to use a CRP poc test.

Tree

CRP on its own has little use, other than verifiying inflamation. My own opinion on POC testing is that not all of it is nessecary. Cost and reliability are big factors that need to be considered. Some of it is very useful, like identifying glucose levels, but im not sure of the requirement for diagnosing non-emergency conditions where an extra couple of days makes little odds to the outcome.

bleg

The technology may well be there, but at the moment it is neither cost effective or feasible. Lab on a chip technology may change that in the future.

maninasia

I know the tech and options are coming on fast now for POC. I think it would be preferable to use a test than to take the chance that patient's diagnosis is wrong and the disease gets worse. Use the concrete data even if it is just to screen out.
I know economics comes into it aswell of course.

MrCreosote

maninasia wrote: »

I know the tech and options are coming on fast now for POC. I think it would be preferable to use a test than to take the chance that patient's diagnosis is wrong and the disease gets worse. Use the concrete data even if it is just to screen out.
I know economics comes into it aswell of course.

You're looking at the tests the wrong way. POC tests are never diagnostic- they just alter the probability it is a certain diagnosis or not. Google Bayesian networks and pretest probability. The cut off for "positive" will be an arbitrarily agreed-on number, so there is still the chance the diagnosis is wrong.

You can't just screen out an illness with a test at POC (at present), you can only make it more or less likely. Clinical examination is just the same of course, another test, just with more variation on the part of the tester.

AmcD

Correct me if I am wrong, but I don't think there is a generic test yet which distinguishes viruses from bacteria. As far as I am aware you have to test for specific pathogens based on clinical suspicion. This is useful in a STI clinic where there is the possibility of doing a HIV test on the spot. However this would be a pretty much useless test when faced with a two year old who is still snotty and pyrexial two weeks after you last saw him.
Even if there was a "virus vs bacteria" test, people can still get bacterial superinfection following a viral illness.
Having said that, I would be happy if there was a quick cheap test that could reassure the parent of the two year old that it was a viral infection and so I was not being contrary in withholding antibiotics.

maninasia

MrCreosote wrote: »

You're looking at the tests the wrong way. POC tests are never diagnostic- they just alter the probability it is a certain diagnosis or not. Google Bayesian networks and pretest probability. The cut off for "positive" will be an arbitrarily agreed-on number, so there is still the chance the diagnosis is wrong.

You can't just screen out an illness with a test at POC (at present), you can only make it more or less likely. Clinical examination is just the same of course, another test, just with more variation on the part of the tester.

Yes every test has a certain false positive/false negative rate. However the clinicians diagnoses false positive/false negative rate may be much higher than the test. So it would make sense to defer to the test first in this case (of course in practice a combination of tests and clinicians examination would be the best course). Use the test to first screen out (to a 1% chance for instance) what could be very similar diseases would make your correct diagnoses rate a lot higher, even if you don't have the full battery of tests available yet.
Why I am interested is because in the scientific world everything is data based, there is very little room for personal interpretation, but it seems medicine is running a little behind with incorporation of molecular tests. For a molecular laboratory it is quite simple to test for the common viral/bacterial diseases, however I'll admit it is harder for quick POC tests (but still possible with many quick flu tests on market).

RobFowl

maninasia wrote: »

Yes every test has a certain false positive/false negative rate. However the clinicians diagnoses false positive/false negative rate may be much higher than the test. So it would make sense to defer to the test first in this case (of course in practice a combination of tests and clinicians examination would be the best course). Use the test to first screen out (to a 1% chance for instance) what could be very similar diseases would make your correct diagnoses rate a lot higher, even if you don't have the full battery of tests available yet.
Why I am interested is because in the scientific world everything is data based, there is very little room for personal interpretation, but it seems medicine is running a little behind with incorporation of molecular tests. For a molecular laboratory it is quite simple to test for the common viral/bacterial diseases, however I'll admit it is harder for quick POC tests (but still possible with many quick flu tests on market).

I suppose the question here is will this test help clarify diagnoses sufficiently to justify the extra time and cost.

I'd say the consensus is that is is neither sensitive nor specific enough to justify the time and extra cost.

That is my experience and also the advice from our local hospital lab.

maninasia

I think the consensus is obvious already, but wondering why that is and if it should change.

tallaght01

The issue is reasonably straightforward, hence the consensus:

There are POC test available for viruses, but none for them all.

There are about 30 common respiratory viruses, and 9 that are REALLY common. So, you'd want to be doing 9 tests on one person to isolate a virus.

I'm unaware of any test for bacterial respiratory pathogens that are available, except one for meningococcal. But until that one has 100% sensitivity, then it won't matter what it says....if the clinical suspicion is there, then they go to hospital. If you're suspicious enough to test for meningococcal, then they need to be in a hospital.

I am not aware of any test that distinguishes bacterial from viral infections. It would be big news if it happened.

Where POC testing has it's uses is in the setting of an epidemic/outbreak. they're available for swine flu/avian flu etc. So, you want to know instantly if people need to be quarantined.....then do a test for a specific pathogen.

As things stand now, there is no place for open ended testing, like you're suggesting, in primary care for very good reasons.

EDIT: By the way, has anyone else got the guff from the makers of the group a strep pharyngitis test? Quoted sensitivity and specificity between 50-100%! Now, is it 50% or is it 100%? Coz that's pretty important :P

maninasia

Its coming along.

https://www.futurity.org/viral-bacterial-infection-antibiotics-2562132/

maninasia

https://www.boards.ie/discussion/comment/67794863#Comment_67794863

You wouldnt want to do nine tests. You would do a multiplex single test, for the nine common ones at minimum.

Anyway the science is advancing and I wish GP clinics advanced with them. The issue is not 'straightforward'.

Obviously doctors should want to know what is actually causing the disease their patient is presenting with to give the most appropriate and accurate and timely treatment. Not just guessing or assuming it is something because it is the most common.