Why do doctors...?

Question

If a doctor thinks you have something wrong.. why do they do every other test first? Why don't they test you for the thing they think is wrong with you.. instead of wasting time testing for other things.. THEN test you for the thing they think is wrong?

EX: If a doctor thinks you have.... ALS.. why don't they test you for ALS? Why do they test other things.. and THEN test for ALS???


Makes no sence to me. Each illness has it's specific diagnostic tests and differential diagnosis. Why would they waste time ruling other things out when they could test for the suspected illness?

I DON'T have ALS, I was just using it as an example cause it was the first short thing that came to mind.

Answer 1

Sorry.... that isn't the way it works.

When we (medical practitioners) evaluate patients we start by taking a medical history. From that history we develop a list of possible problems. Or a differential diagnosis.

Then, we perform a physical examination. The physical is designed to confirm or deny a suspicion and there by remove or add other diseases to the differential diagnosis.

Laboratory, radiologic and other ancillary testing is done to further narrow done the list.

Unfortunately, because people distort their symptoms or labs are not clear cut, we can be led astray and must re-evaluate things.

It amazes me how many people think that practicing medicine is a clear cut exercise in logic and deduction. It is not. People are different an as such present with different symptoms.

If your doctor is having a hard time making a diagnosis, it may very well be because you are not giving him/her enough information.

Just something to think about.

Answer 2

Sometimes in order to make a definitive diagnosis you must rule out all other possibilities because if you do not, symptoms similar to a certain disease could have been caused by something much simpler than a severe disease like ALS. For example, a symptom might be muscle stiffness and slurred speech, but it is possible that the slurred speech and weakness could have been caused by a minor stroke or TIA. These possibilities must be ruled out before diagnosing a patient with ALS. It would be irresponsible not to rule other possibilities out.

I mean if you go into a hospital and your symptom is that you are fatigued and certain things in your family indicate that you might have leukemia, don't you think they should rule out things like mononucleosis before testing for cancer??? Some tests are more expensive than others, and if there is a simple solution possibly, that is the one the doctor will go for first if symptoms are suggestive, but by no means definitive of a severe condition.

Answer 3

It very much depends on the disease.

If a doctor suspects you have a certain condition on the basis of taking a history from you and examining you then they will order that test first. At the same time, we tend to test people for simple things that are less uncomfortable for the patient first (it's a lot less hassle for a patient to have a blood test than a colonoscopy, for example).

In some cases, some diseases we may suspect cannot be firmly diagnosed positively - they are essentially diagnoses of exclusion. With your specific example, ALS, you cannot firmly diagnose it just on any one test. Various tests are suggestive, but the key thing is to make sure that the patient does not have any other condition. ALS is a devastating condition, and I have personally seen the effects of a patient being mislabelled as having the condition when they haven't. The same thing applies to Alzheimer's Disease, for example.

Answer 4

The truth is, not all illnesses have a definitive test that can give you an absolute diagnosis. The majority of medicine is ruling things out to come up with a diagnosis, not just testing to see if their proposed diagnosis is correct. If every disease had an absolute diagnostic test, then it would not be very hard to become a doctor.

Answer 5

Two reasons: (1) Medicine is really a guessing game. Doctors don't really know what's wrong with you when they subject you to a bunch of tests. They may have a pretty good idea, but...(2) Some medical tests are much more expensive than others. You mentioned one of the most expensive -- the test for ALS -- so they'll usually test you for other possibilities (remember, they're never 100% sure what's wrong with you) before ordering that very expensive test that'll cost their patient a lot of money for a co-pay.

Answer 6

It is unusual but they have to cover their bases since people sue at the drop of a hat (which will result in higher costs, lowered paid doctors and hence less doctors leading to more deaths..good job people!).
There is also something my friend told me that there are baselines that have to be done because the baseline conditons mutate so much that even though looks like ALS could be strep or something and the medicine for ALS could make the other worse

Answer 7

Not so fast there. There are a lot of diseases that are similar in nature. Some diseases (like multiple sclerosis and others) are usually diagnosed after ruling out all other maladies. Also, since some diseases are so similar in nature, they have to do certain tests to determine which one (either, or) that you have. They have to make sure that your symptoms are/are not a certain disease or related to some bigger/different issue.


It is not about the money. I work in healthcare, I see the reimbursements that doctors get. It isn't the "well paying" job it used to be. Granted, it doesn't pay minimum wage, but most doctors aren't making billions off of their practice.

Answer 8

cuz for any disease the manifestations would be few general sypmtoms & few specific symptoms...

say u have a fever... they may be sue to many causes

they first do a complete blood check up ...to see ur antibody levels...
check if u have any infection/jaundice etc..
then do a confirmatory test.


this is the usual procedure -->

1 patient complaint
2 ask patient history
3 clinical examination
4 differential diagnosis ( like it may be this or that)
5 investigations (blood,stool, xray)
6 confirmatory diagnosis... (u have fever due to an infection)

got it ?

Answer 9

It all comes down to the issue of liability. He tries everything else, because if he diagnoses you with ALS, and it turns out that you have something that is still serious but less likely to be terminal, you can turn around and sue him for deliberately causing "undue mental anguish" or some such.

Answer 10

I think it's because doctors are never 100% sure of themselves, and need to rule out possible reasons for the original illness.