G6PD deficiency and enzymopathies: Case

This boy has an acute haemolytic crisis of glucose-6-phosphate dehydrogenase deficiency triggered by fava beans, the classic Mediterranean favism. His ancestry, the fava bean exposure two days earlier, the sudden pallor with dark urine, the severe anaemia with a high reticulocyte count, the negative direct antiglobulin test, and the blood film with bite cells, blister cells and Heinz bodies make the diagnosis secure at the bedside. The mild cough is the kind of incidental infection that can also be a trigger, but here the fava beans are the dominant precipitant. ^[1][10]

Clinical findings and differential

The key findings are the Mediterranean ancestry, the fava bean exposure, the severe anaemia with a reticulocytosis, and the direct-antiglobulin-test-negative intravascular haemolysis. The blood film is the discriminator: bite cells and blister cells with Heinz bodies on supravital staining point to oxidative haemolysis, and the negative direct antiglobulin test rules out immune causes. The differential includes hereditary spherocytosis, which would show spherocytes and a family history of splenectomy or gallstones, autoimmune haemolysis, which would be direct-antiglobulin-test-positive, and pyruvate kinase deficiency, which causes chronic haemolysis without oxidant dependence and without Heinz bodies. None of these fits as well as G6PD deficiency here. ^[1]

The candidate should synthesise the problem representation aloud: a sudden onset direct-antiglobulin-test-negative intravascular haemolysis in a boy of Mediterranean ancestry after fava beans, until proven otherwise G6PD deficiency. The spleen tip is consistent with the mild splenomegaly that accompanies acute haemolysis. The severity, with a haemoglobin under 70 g per litre, places him in the transfusion category. ^[1]