Case #184 – July, 2006

A patient went to a local hospital with fevers and thrombocytopenia after recent travel to Haiti. A blood smear examination was requested by the attending physician. Figure A shows what was seen on a Wrights-Giemsa stained thin blood smear; the image was taken in a thicker area of the smear and low numbers of these objects were found in the smears. What is your diagnosis? Based on what criteria?

Figure A

The object shown in this case was an artifact, and a diagnosis was given of No Parasites Found (NPF). The artifact did resemble a gametocyte of Plasmodium falciparum. Although the size of the object, estimating from the size of clumped red blood cells surrounding it, is within the range for gametocytes of P. falciparum, key morphologic features were absent. Figure A below shows P. falciparum gametocytes; some of the diagnostic features of these gametocytes were not seen in the object in the original case image, and include:

yellow and/or brown pigment which is normally seen in gametocytes of Plasmodium sp. (Figure B, black arrows).
reddish-staining chromatin (Figure B, purple arrows).

Figure B

Staining can be variable based on type of stain used and pH. Ideally, at least two to three colors, blue (parasite cytoplasm) and red (chromatin), should be visible with pigment being golden yellow to dark brown.