Metamizole (dipyrone) as an interferent in biochemical assays

BackgroundMetamizole (MMZ), commonly used as an analgesic/antipyretic in countries like Spain, faces restrictions elsewhere due to side effects. Despite this, its frequent use underscores the critical importance of studying its impact on the accuracy of laboratory tests, particularly when blood samples are obtained shortly after intravenous administration.MethodsTo investigate the in vitro interfering effect of MMZ, 20 serum biochemical assays were selected. The concentrations of biochemical assays were measured in a serum pool spiked with increasing MMZ concentrations. For each assay, the percentage of interference was calculated and compared with our laboratory's quality requirements for bias.ResultsIn vitro interference was observed in some biochemical assays: cholesterol (CHOL), creatinine (CREA), high-density lipoprotein cholesterol (HDL), lactate (LAC), lactate dehydrogenase (LDH), triglycerides (TG) and uric acid (UA), leading to falsely reduced results. All of them, except for the LDH assay, exhibited clinically significant interference with CREA being the first to be affected at a metamizole concentration of 0.31 g/L. No interference was observed in the remaining assays.ConclusionsFalsely decreased and clinically significant CHOL, CREA, HDL, LAC, TG and UA results were observed in serum samples due to in vitro interference caused by MMZ contamination. Serum concentrations in patients receiving intravenous MMZ treatment may be falsely decreased due to interference by MMZ. Knowledge of such interferences in clinical laboratories is crucial for the correct diagnosis and treatment of patients.