Abstract
A 75-year-old woman with rheumatoid arthritis showed a discrepancy between the reduced level of serum γ globulin on cellulose acetate electrophoresis and the normal level of serum IgG determined by laser nephelometry. Although no M-peak was detectable on cellulose acetate electrophoresis, immunoelectrophoresis of the patient's serum revealed a monoclonal protein reacting with anti-IgG antiserum but not with anti-κ or anti-λ light chain antiserum. Western blotting of the patient's serum showed abnormal low-molecular-weight γ chains. Thus, the patient was diagnosed with γ heavy chain disease. A comparison of γ globulin levels determined by different methods may be useful when screening for this disease.