Pregnancy-specific beta 1-glycoprotein in serum in monoclonal gammopathies: relationship with serum beta 2-microglobulin, and cellular origin.

Pregnancy-specific beta 1-glycoprotein (SP1) was assayed by particle-counting immunoassay in serum from 86 healthy blood donors and 236 patients with various types of gammopathy. A concentration of 1 microgram/L was taken as the upper normal limit. Abnormally high values were found in one of 10 patients with monoclonal gammopathy of undetermined significance, in 65% of 152 patients with multiple myeloma, in 84% of 64 patients with Waldenström's macroglobulinemia, and in seven of 10 patients with monoclonal gammopathies associated with other myeloproliferative disorders. In a study of 90 myeloma patients, the SP1 value correlated (p less than 0.001) with the concentration of beta 2-microglobulin in serum, a value which had been corrected for possible renal dysfunction, but not with the concentration of the monoclonal component. SP1 was detected by direct immunofluorescence in myeloma cells of bone-marrow smears from six of 10 patients with myelomatosis. These six patients had serum SP1 values greater than 1 microgram/L, whereas the four patients with fluorescence-negative myeloma cells had SP1 values less than 1 microgram/L.