This patient's glucose-6-phosphate dehydrogenase (G6PD) activity should be measured in 2 months. G6PD deficiency is an X-linked disease and occurs more commonly in men, often in blacks. This variant typically leads to episodic hemolysis in response to oxidant stressors (for example, infections or drugs such as dapsone, trimethoprim-sulfamethoxazole, and nitrofurantoin). Elevated levels of G6PD are found in normal young reticulocytes, and levels may appear falsely normal during an acute hemolytic episode, causing a missed diagnosis. Consequently, G6PD levels should be checked a few months after the occurrence of an acute event. During an acute hemolytic episode, bite cells may be seen on the peripheral blood smear, as are apparent in this patient's peripheral blood smear.
Thrombotic thrombocytopenic purpura (TTP) should be suspected in patients who have anemia, schistocytes on the peripheral blood smear, increased serum lactate dehydrogenase level, and thrombocytopenia. TTP can be triggered by drugs, especially quinine, ticlopidine, mitomycin C, cyclosporine, or gemcitabine. The mechanism of disease is thought to be antibodies directed against the protease ADAMTS-13 that is responsible for cleaving the high-molecular-weight multimers of von Willebrand factor. Assays for ADAMTS-13 activity are available but are not needed for a TTP diagnosis and are not indicated in patients who lack the essential diagnostic criteria for TTP.
Hereditary spherocytosis should be suspected in patients with a personal or family history of anemia, jaundice, splenomegaly, or gallstones. Spherocytes are present on the peripheral blood smear, and the direct antiglobulin (Coombs) test is negative. The osmotic fragility test with 24-hour incubation is a key diagnostic step, demonstrating increased erythrocyte fragility in hypotonic saline compared with control erythrocytes. This patient's ethnic background, absence of splenomegaly, and presence of bite cells on the peripheral blood smear do not support a diagnosis of hereditary spherocytosis.
