PROTEIN PRECIPITATION AS A POSSIBLE IMPORTANT PITFALL IN THE CLINICAL CHEMISTRY ANALYSIS OF BLOOD SAMPLES CONTAINING MONOCLONAL IMMUNOGLOBULINS: 2 CASE REPORTS AND A REVIEW OF THE LITERATURE. PROTEIN PRECIPITATION AS A POSSIBLE IMPORTANT PITFALL IN THE CLINICAL CHEMISTRY ANALYSIS OF BLOOD SAMPLES CONTAINING MONOCLONAL IMMUNOGLOBULINS: 2 CASE REPORTS AND A REVIEW OF THE LITERATURE

Two case reports are presented, both illustrating an analytical interference caused by monoclonal im- munoglobulins. Falsely low results were obtained in the routine analysis of glucose, CRP and HDL-cho- lesterol. When analysing samples containing paraproteins, various problems can be encountered in the clinical laboratory: next to the antibody effect, pseudohy- ponatraemia, hyperviscosity, cryoglobulinaemia and gel formation have to be taken into account. In our two cases the interference was caused by paraprotein precipitation, causing an increased turbidity and an ap- parent increase of light absorbance at every wavelength due to light scattering, including the wavelengths used in the clinical chemistry assays. We review the lit- erature on this sometimes overlooked interference in photometric/turbidimetric assays. This reaction is based on the insolubility of these proteins in specifi c physico-chemical circumstances in which many varia- bles are involved, among others: pH and ionic strength, presence of preservatives and surfactants in the assays, pI and other specifi c properties of the monoclonal im- munoglobulins. The complexity of the problem makes predicting or preventing this probably infrequent in- terference usually impossible. This artifact can cause both false positive and false negative results in mul- tiple parameters (e.g. bilirubin, creatinine, iron, urea, uric acid), the most frequently reported analyte being phosphate.