Lisa Sanders MD’s New York Times Diagnosis column told of a 73-year-old woman with rapid onset anemia. She had malaise, shortness of breath and episodes of drenching sweating, but no blood in her stool and no mention of a medication history. Many conditions with a wide variety of causes can present with this picture (SimulConsult subscribers can click on any of the images to load the case in the software):
The article doesn’t mention the results of a Comprehensive Metabolic Panel or basic electrolyte and renal test, but it is hard to imagine that neither was obtained. We would have been told if the Blood Urea Nitrogen finding in these tests was elevated, so we will consider that finding to be absent:
Adding the absence of BUN elevation produces a differential diagnosis featuring infectious diseases, and other than commenting on other results in the comprehensive metabolic panel, the next most useful test is a blood smear, in which the most useful finding is checking for the Babesia parasites that cause Babesiosis, which turned out to be the diagnosis. This test was ranked high not just because of the match with the differential diagnosis, but also because Babesiosis is curable.
The excellent curation of Babesiosis by Nicole Nadeau MD of Massachusetts General Hospital was important in making an unusual diagnosis easily solvable.