We observed a patient with IgG4-λ type M-proteinemia whose serum albumin (ALB) value elevated higher than total protein concentration (TP). The patient’s serum showed abnormality in not only ALB but also direct bilirubin (D-Bil) and iron (Fe) with an automated chemical analyzer. Blood chemistry findings were: TP 8.8 g / dl; ALB 9.2 g / dl; D-Bil –6.2 mg / dl; and Fe 25 μg / dl. The measurements of ALB, D-Bil, and Fe by automated chemical analyzer showed abnormal time course in the reaction and the precipitates were formed by the interaction between the patient’s serum and each reagent. Immunofixation electrophoresis revealed that these precipitates were the IgG4-λ type M-protein. The purified patient’s IgG4 molecules were found to be composed of two γ4 chains of 55 kDa and two λ chains of 24 kDa by Western Blotting analysis. To be common to three reagents was used to acidic buffer solution, approximately pH 4.0. Therefore, it is thought that the precipitates are occurred under the acidic conditions. This phenomenon may be caused by amino acid composition in the variable region or glycosylation of M-protein rather than conformational abnormality such as deletion of a domain in the constant region.
