Blog | Wednesday, October 12, 2011

Laws of thermodiagnostics


A tongue in cheek application of the Laws of Thermodynamics as applied to medicine:

0th: If two diagnostic findings support a third, then they must support each other. No single diagnostic finding has ever made a diagnosis. It is a careful process of combining and comparing data that makes it possible to reach a diagnostic conclusion. Look at what your "facts" are. The diagnosis with the most "facts" supporting it is most likely the right one. Of course, facts in medicine are not as concrete as we would like to make them seem as demonstrated by false positive and negative results.

1st: You cannot win. A physician's diagnostic performance can be of one form (i.e. specific or sensitive) or another, but cannot be both. If you rule out a lot of different etiologies without ever ruling one in you are highly sensitive but not specific, and your patient still doesn't know what is wrong with them. If you always get positive results to your diagnostic inquiries you are highly specific but not very sensitive, and you are probably missing some disease in other patients because of missed testing.

2nd: You cannot break even. A negative diagnostic work-up does not decrease morbidity or mortality, while a positive one always increases both. Just because you didn't find a pathophysiological reason for a presentation doesn't mean that you didn't miss something or that your patient is any safer from future insults. Confirming a diagnosis simply means that you have named the disease and they now have the same increased risks as others with that disease as well as those from related or unrelated future insults.

3rd: You cannot leave the game. Absolutely false results must be worked-up, as there are no absolutes in medicine. Even the most spectacularly sound medical reasoning for explaining a false positive or random incidentaloma means nothing without further testing to corroborate that reasoning. Missed diagnoses kill, maim and get doctors sued.

ACP Member Mike Aref, MD, PhD, is an academic hospitalist with an interest in basic and clinical science and education, with interests in noninvasive monitoring and diagnostic testing using novel bedside imaging modalities, diagnostic reasoning, medical informatics, new medical education modalities, pre-code/code management, palliative care, patient-physician communication, quality improvement, and quantitative biomedical imaging. This post originally appeared at his blog, I'm dok.