Paroxysmal cold hemoglobinuria and the elusive Donath-Landsteiner antibody

Four patients with paroxysmal cold hemoglobinuria (PCH) illustrate some of the difficulties in making the diagnosis. A 46-year-old male presented with anemia, a weakly positive direct antiglobulin test (DAT) with anti-IgG, a haptoglobin < 0.1 g/L, and a cold autoagglutinin showing anti-P specificity. A 9-year-old female had a 4-day coryzal illness, a 20 g/L fall in hemoglobin over 24 hours, and a haptoglobin < 0.1 g/L; the DAT was positive with anti-C3d. A 3-year-old female was referred following a rapid drop in hemoglobin of 30 g/L; the DAT was positive with anti-C3d. A 17-month-old female, unwell for 2 weeks, had a hemoglobin of 41 g/L; the DAT was strongly positive with anti-C3d and weakly positive with anti-IgG and -C3c. In all patients, PCH was confirmed by positive indirect Donath- Landsteiner tests, and the autoantibodies demonstrated P specificity. In two patients, the test was strongly positive; in the third patient, it was only positive using papainized red cells; and in the fourth patient, a two-stage papainized procedure was needed before a positive result was obtained. PCH must always be considered in a child with a rapid drop in hemoglobin, even if initial tests are negative.