Pathology

Biography

Biography: Lu Song

Abstract

Immunoglobulin paraprotein present in patient serum samples can interference with various chemistry methods causing erroneous results. The mechanisms of the interference have not been clearly elucidated or understood. Using samples containing various types of paraproteins, we studied the interference of paraprotein with the direct bilirubin, creatinine and total protein assays on the Beckman Coulter AU5400/2700 platforms. Repetitive testing of some of the samples exhibiting interference revealed a pattern of fluctuation in test results. Protein precipitation was observed when the reactions were scaled up 10 fold in a test tube. Aggregates of paraprotein can scatter light resulting in altered absorbance. Furthermore, removal of paraproteins by ultra filtration can eliminate the interference providing evidence that paraprotein precipitation being the cause of the interference with chemistry tests. We performed experiments at various pH and ionic strength to demonstrate that at extremely high (pH 12-13) or low ionic strength as that in the creatinine assay, an IgM paraprotein formed large aggregates. After testing additional samples containing immunoglobulin paraproteins from different patients, we can show that different paraproteins behaved differently in response to changes in pH and ionic strength possibly due to the individual set point determined by amino acid compositions of each monoclonal paraprotein. We conclude that pH and ionic strength are the key factors that contribute to protein aggregation and precipitation which interfere with the measurements of creatinine assay. Therefore, one should consider the possibility of paraprotein interference if the results are irreproducible. Understanding the mechanisms of interference by paraproteins and be able to recognize such interferences can help clinicians to troubleshoot the problem with chemistry tests.