When I was a medical student, lab test interpretation was a difficult area for me. Not much has changed since then because the students I work with, like many of you, continue to struggle with lab test interpretation. In my opinion, it's an area that doesn't get the emphasis it deserves during medical school. We just don't do a good job of teaching lab test interpretation to students.
As those of you who are doing clerkships have already seen, abnormal lab tests are quite common, especially in hospitalized patients. Almost every patient who gets admitted has a battery of tests that is routinely ordered and more often than not, at least one of the tests is abnormal.
If you are working up a new patient and you find one or more abnormal lab test results, here's what I suggest that you do:
1) Look up the differential diagnosis for the abnormal lab test - a lot of students stop right here but the honors student takes it several steps further (see below)
2) Try to determine if the abnormality supports or confirms your working diagnosis (i.e., the diagnosis you think the patient has based on the history and physical).
3) If it doesn't seem to have anything to do with the working diagnosis, ask yourself if it supports one of the other diseases in the differential diagnosis of the patient's complaint. If it does, you may have to rethink your working diagnosis.
4) If it doesn't have anything to do with the patient's clinical presentation, then try to develop an approach for determining what the cause of the abnormality is. Your attending may very well ask you "what do you want to about this abnormal lab test".
Some lab tests that you order may take days to come back. For these pending lab tests, while waiting for their return, it's a good idea to read up on them so you know what to do should they come back abnormal. Too often, students wait for the results of these pending tests and then when they come back abnormal, they are not sure what to do because they didn't read about them. To avoid this situation, ask yourself what will I do if this test comes back abnormal. That way, when the test does come back abnormal, you can turn to your resident or attending and say "this is what I believe we should do". Residents and attending physicians are often pleased with this type of response because it shows them that you are problem-solving. By the way, problem-solving skills is an area on the evaluation form that attendings and residents are asked to comment on.
Just some tips on lab test interpretation - hope it helps,
Samir Desai, MD
Assistant Professor of Medicine
Baylor College of Medicine
