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Paraprotein interferences assays are known but rather unusual in clinical chemistry.we here report a paraprotein interference with a bicarbonate assay in a IgA kappa-type myeloma patient. Serum bicarbonate level was assessed by the enzymatic method of a multiparametric chemistry analyzer (Advia 1800, Siemens) as well as a specific electrode assay on a blood gas analyzer (GEM 4000, IL). Paraprotein interference with the enzymatic assay was evidenced by an abnomally low bicarbonate level measured by the enzymatic method in contrast with usual levels obtained by using the gas analyzer and with the clinical status of the patient. Therefore, gammapathy has to be taken into consideration when interpreting biological data.

Vitamin D (Vit.D) and parathormone (PTH) measurements are usually prescribed for phosphocalcic metabolism assessment and, especially for Vit.D, more and more frequently for other pathologies. In order to step up to automated techniques for these analysis in our laboratory, we tested 3 devices: ADVIA Centaur XP(®) (Siemens), ISYS(®) (IDS) and Liaison(®) (Diasorin), which allow to simultaneously quantify Vit.D and PTH. The aim of this study was to evaluate the fidelity of these methods as well as study the correlation between them and the radioimmunological techniques previously used in our laboratory : « ELSA PTH » (Iba Cisbio International) and « 25-OH D » (IDS). The comparison of PTH analysis was performed on a population of chronic renal failure patients undergoing haemodialysis. According to our study, the 3 devices show acceptable analytical performances; anyway the measurements realized on the ISYS analyzer are the ones showing the best results in terms of fidelity, and the closest results to those obtained with the RIA reference techniques.

L-carnitine is a quaternary ammonium compound that facilitates long-chain fatty acids crossing through the mitochondrial membrane allowing their beta-oxidation. Human pathologies relatives to carnitine are mainly deficiencies, with myopathy and lipids metabolism disorders. The aim of this study was to validate the free and total carnitine plasmatic level measurement using the Dimension HM, X-Pand model analyzer (Dade Behring). Free carnitine was directly determined on plasma samples, deproteinized by using ultrafiltration, whereas total carnitine was measured after alkaline hydrolysis. Within-day and between-day imprecision were < 4,00 and 9,00 % respectively. The method is linear through 250,00 micromol/L and the limit of quantification is 3,00 micromol/L. Our method was correlated to tandem mass spectrometry (r = 0,956 for free and total carnitine). Recovery of free and total carnitine from spiked plasmas was > 99 %. On board stability of cartridge (5 days) and of calibration (at least 30 days) are in agreement with a method easily adaptable in routine laboratories.