Prevalence of small monoclonal proteins in the serum of hospitalized patients.

Small, often multiple, homogeneous bands were observed in the gamma globulin region upon agarose gel electrophoresis of serum from only one of 140 healthy blood donors, but in 10-65% of hospitalized patients. The bands were more frequent if the gamma globulin concentration was high or an acute phase reaction was present. The frequency of bands was unrelated to the age, race, or sex of the patient or to the medical diagnosis. One third of the bands could be characterized at least partially as monoclonal immunoglobulin; a small percentage represented C-reactive protein. Small homogeneous bands, often definable as monoclonal immunoglobulins, are common in the serum of hospitalized patients, and need not imply the presence of a lymphoproliferative disorder. They may reflect a form of human immune response with restricted heterogeneity.