Economic rewards for blood donation: validity of the donor questionnaire as litmus test.

Blood can form a gel when there are high concentrations of proteins, such as IgM and/or IgG antibodies, that precipitate at low temperatures (cryoglobulins) or agglutinate red blood cells (cold agglutinins) (1, 2 ). A bone marrow biopsy performed on this patient revealed Waldenström macroglobulinemia, which produces large amounts of IgM (3, 4). Warming this patient’s sample in a water bath, keeping it on heat packs during transport, and diluting it with warm diluent can reliquefy the sample.