An anti-i biphasic hemolysin in chronic paroxysmal cold hemoglobinuria.

Paroxysmal cold hemoglobinuria (PCH) was diagnosed in an elderly patient with a history of chronic lymphocytic leukemia. In this case, the Donath-Landsteiner antibody demonstrated anti-i specificity rather than the more commonly reported anti-P specificity. This unusual case of a biphasic hemolysin with anti-i specificity emphasizes the importance of performing a Donath-Landsteiner test when presented with serological or clinical findings that are suggestive of PCH.