Paraproteins are a common cause of interferences with automated chemistry methods.

Context: Previous studies have shown that paraproteins caused spurious results on individual analytes including total bilirubin (TBIL), direct bilirubin (DBIL), or HDL-cholesterol (HDL-C). Studies demonstrating paraprotein interferences with multiple analytes measured by different analyzers have not been reported.

Objective: To systemically investigate interferences of paraproteins on TBIL, DBIL, and HDL-C measured by the Roche MODULAR and the Olympus AU2700.

Design: Eighty-eight serum specimens with monoclonal gammopathies were analyzed using the Roche MODULAR and the Olympus AU2700. Paraprotein interferences with the MODULAR and AU2700 were identified by abnormal absorbance curves and confirmed by results from the Ortho Vitros 950 or inconsistent laboratory information.

Results: Spurious results occurred in 89 of 528 measurements; 29 specimens did not demonstrate any interferences whereas 26 specimens gave spurious results in 2 to 4 of the 6 assays. Paraprotein interferences caused spuriously high levels of TBIL in 4 sera measured by the MODULAR. In contrast, paraprotein interferences on DBIL were observed by at least 1 method in 44% (39/88) of sera assayed, occurring almost exclusively with the AU2700. Paraprotein interferences with HDL-C results were present in 35% of specimens assayed with the MODULAR and 16% of specimens assayed with the AU2700. In specimens with interferences, spuriously low AU2700 DBIL, MODULAR HDL-C, and AU2700 HDL-C results occurred with 28%, 90%, and 91% of specimens, respectively.

Conclusions: We demonstrated that paraprotein interferences with TBIL, DBIL, and HDL-C are relatively common and provided explanations why these interferences occurred. Although it is difficult to predict which specimens cause interferences, spurious results appeared method and concentration dependent.