Massive intravascular hemolysis without serum haptoglobin depletion.

Hyperplasia of marrow histiocytes with extensive hemophagocytosis was found in a patient with cytomegalovirus infection. He experienced massive intravascular hemolysis, but, unexpectedly, no depression of the serum haptoglobin level was found by either single radial immunodiffusion or rate nephelometry. The unexpectedly high haptoglobin value may have been the result of "blockade" of the monocyte-macrophage system, with resultant failure to clear haptoglobin-hemoglobin complex rapidly from the circulation. Use of the techniques described for the indirect estimation of unbound serum haptoglobin alone should avoid confusing results in similar clinical circumstances.