Correlation between serum IgG, platelet membrane IgG, and platelet function in hypergammaglobulinaemic states.

Abstract

Summary. Platelet membrane IgG levels were measured by the complement lysis inhibition test, and were correlated with serum IgG levels in 29 patients with elevated immunoglobulins due to multiple myeloma, benign monoclonal gammopathy, systemic lupus erythematosis, rheumatoid arthritis, benign hypergammaglobulinaemic purpura and systemic infection. Platelet membrane IgG was increased in proportion to the elevation of serum IgG with a highly significant correlation coefficient (0.5615, P≤0.01), irrespective of the underlying disease state. Further washing of the platelets did not significantly alter the amount of membrane bound IgG. Qualitative platelet defects were present in nine of the 10 myeloma patients in whom platelet aggregation, platelet factor 3 availability, platelet adhesion to glass beads and bleeding times were studied. The most severe abnormalities occurred in those patients having the highest levels of platelet membrane IgG. Platelet function was normal despite markedly elevated platelet bound IgG in one patient with benign hypergammaglobulinaemic purpura. These findings indicate that elevation of serum IgG must be excluded before inferring the presence of platelet autoantibodies in patients with elevated platelet bound IgG. They also support the concept that the qualitative platelet abnormalities seen in multiple myeloma result from platelet coating by abnormal immunoglobulins or are secondary to myeloma effect on bone marrow.