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Aims: Analytical interference in the clinical laboratory is a well-known phenomenon. When analyzing samples containing monoclonal immunoglobulins (M proteins), various problems could be encountered in the clinical laboratory data.
Presentation of Case: The authors report a patient with false elevated plasma creatinine concentration due to interference of monoclonal IgM in a routine test for creatinine determination. In the present case the interference might be caused by M protein precipitation, due to an increased turbidity and an apparent increase of absorbance in the clinical chemistry creatinine assay. Sia water test can provide a first clue to M protein aggregation; confirmation can be obtained by observing the time/absorbance curves of the analysis. When a Sia water test was performed with changes in the salt concentration, protein aggregation occurred at a higher salt concentration for the lithium (Li)-heparin plasma sample than the serum.
Discussion and Conclusion: These results suggested that the M protein of this patient, when interacted with Li-heparin, is more readily insolubilized. Subsequently, a reaction reproduction experiment was performed by adding the M protein component roughly purified to Li-heparin blood collection tubes. These results might support the aggregation of the M protein of this patient in the reaction solution due to its interaction with Li-heparin.