As a mathematician I am quite puzzled by the weird way that medicine understands itself as a science. But there are some basic techniques that can recover some of the scientific spirit in everyday life and one of them is probabilistic reasoning, of which the core is Bayes theorem. Now we had a session once that covered the intricacies of odds vs. probabilities in using Bayes theorem, but perhaps it is more in order to discuss the theorem itself, so that is what we did on Tuesday, using the case of D-dimer for sinus thrombosis, where a sensitivity of “only” 94% is used to discredit it’s use as a rule-out criterion both in the guidelines and in reviews by many german writers.

So consider any headache (as we now know, it usually is non-specific) in the ER and estimate the possibility of it being an SVT. Then use the sensitivity and specificity of the test to come up with post-test probability after D-dimer is negative and positive.


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