Gammopathy interference in clinical chemistry assays: mechanisms, detection and prevention

Monoclonal gammopathy is characterized by the presence of an M-protein in serum or urine that has homogeneous structural and functional properties. It can occur in very high concentrations and may cause significant interference in clinical chemistry assays. Examples of gammopathy interference for the analytes glucose, bilirubin, gamma-glutamyltransferase, urea and ferritin are presented. Various mechanisms of interference are described, such as the production of turbidity by the M-protein and the binding of the M-protein to a component of the test system or analyte. In immunoglobulin tests, the M-protein is the analyte itself and may not be completely bound by the test antibody owing to its structural properties. Modern analyzers can detect unusual changes in absorption during the course of a reaction, and thus the formation of turbidity due to M-proteins. This interference may be prevented by optimizing the buffering conditions of the reagents to avoid the formation of turbidity or by removal of the M-protein prior to analysis of the sample. Owing to the unique properties of each M-protein, it is impossible to protect common clinical chemistry test systems completely from gammopathy interference. Therefore, efficient ways for the detection of such interference are needed.