Answer to Case 494

Answer: Malaria due to Plasmodium falciparum; >20% parasitemia
There were lots of great suggestions for what the lab should do after making this identification. The step of primary importance is to urgently contact the clinical team to relay the result and ensure they understand the importance of the diagnosis. In my laboratory we treat all malaria diagnoses as critical results. In this case, the causative agent (P. falciparum) and the high parasitemia (>2%) make this call even more urgent, since the patient is at very high risk of death from his infection and requires immediate treatment.

In addition to antimalarial treatment (e.g. IV quinidine or artesunate), red blood cell exchange may also be performed for patients with >10 % parasitemia. While the United States Centers for Disease Control and Prevention (CDC) no longer recommends red cell exchange for severe malaria, many other groups such as the American Society for Apheresis (ASA) feel that it is still warranted in life-threatening infections such as this one. You can read the arguments for red blood cell exchange for malaria with >10% parasitemia here:

CDC paper arguing AGAINST red cell exchange for severe malaria:
https://www.ncbi.nlm.nih.gov/pubmed/23800940

Counter argument from the ASA:
https://academic.oup.com/cid/article/58/2/302/333989

Thanks to everyone who wrote in on this case, and kudos to those who took the time to calculate the % parasitemia!