Background: Conventional biochemistry parameters employ the use of photometry and enzymatic reactions which reduce the possibility of analytical errors. On contrary, tests performed with immunoassay are known to be more prone to analytical interferences and may subsequently yield incorrect values. Case presentation: We present two cases investigated due to very high levels of vitamin D in the serum that exceeded the measurable limit of the analyzer. Protein electrophoresis showed a monoclonal peak, revealing elevated immunoglobulin G and elevated immunoglobulin M respectively. Gold standard analysis of vitamin D using liquid chromatography-mass spectrometry revealed normal vitamin D concentrations in both cases. Further, bone marrow puncture revealed a diagnosis consistent with multiple myeloma and Waldenströms macroglobulinemia. Conclusion: Falsely elevated levels of vitamin D exceeding the maximum measurable limit is highly suspicious. Although analytical interference in immunoassay is limited, we should keep in mind that results obtained by this method are more prone to analytical errors.

Keywords: immunoassay interference, 25(OH) vitamin D, falsely elevated, paraprotein, case report