Repeated USMLE Questions Step 1- 305

A week old female presents for her first checkup. Examination reveals jaundice and splenomegaly. Laboratory investigations show:

Total bilirubin level: 27 mg/dL

Direct bilirubin: 0.6 mg/dL

Hgb: 10.1 g/dL

Reticulocytes: 6%

A blood smear shows burr cells and spherocytosis.

Which of these tests will be positive in this patient?

A-Acid hemolysis test

B-Coomb’s test

C-Osmotic fragility test

D-Metabisulfite test

E-Schilling test


This is a case of hereditary spherocytosis. Osmotic fragility test is diagnostic in this patient. Spherocytes lyse at a higher concentration of salt than normal red blood cells which causes an increased osmotic fragility. Acid hemolysis test is used to diagnose cases of paroxysmal nocturnal hemoglobinuria while Coomb’s test is used in diagnosis of autoimmune hemolytic anemia. Metabisulfite test is used in sickle cell anemia and Schilling test is used in cases of pernicious anemia.

The correct answer is C

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