[Improving the interlaboratory variation for creatinine serum assay]. / Dosage de la créatininémie en 20003: état des lieux analytique et essai de standardisation de l'étalonnage.

PURPOSE: To assess inter-assay variation and accuracy of blood creatinine measurements as well as the effect of the standardization of the calibration procedures on inter-assay variation. METHODS: Inter-assay variation and accuracy were assessed using 30 frozen human sera and 3 certified reference materials, which were analysed by 17 creatinine assays (colorimetric: 12, enzymatic: 4, HPLC: 1). Usual calibration procedure was compared with two common calibration procedures using either a reference material (404.1 micromol/L), or secondary sera calibrators (69, 115 et 180 micromol/L). RESULTS: Most of the commercially available methods display inaccuracy, > 10% for creatininemia < 150 micromol/L in most cases. For this concentration range, the mean creatininemia was statistically significantly different as a function of the assay used (p < 0.001). Enzymatic assays produced lower results than colorimetric ones for low creatinine levels but higher results for high creatinine levels. Assays being calibrated according to the manufacturer's recommendations, the median dispersion factor was 14% for the 20 samples between 45 and 150 micromol/L, and 8% for the 10 samples between 250 and 350 micromol/L. The calibration procedure modified inter-assay variation significantly (p < 0.001) but we gained little advantage from both common calibration procedures. A significant decrease of inter-assay variation occurred within each technical group (colorimetric or enzymatic) when a common calibration was performed using calibrators which concentration(s) was(were) close to the concentrations to be measured. CONCLUSIONS: Inter-assay variation is too high to allow prediction of glomerular filtration rate (GFR) or creatinine clearance from serum creatinine level. Our results highlight the interest of a calibration procedure using several concentrations with at least one between 90 and 150 micromol/L. The marketing of such a calibrator should be considered in order to decrease inter-assay variation in the range of creatinine levels which defines a mild chronic renal failure. Such an approach will certainly reduce inter-assay variation only within each technical group but could allow to include technical group as a co-variable in the algorithms developed for predicting GFR or creatinine clearance. A global transferability will certainly need the correlation of all types of creatinine assays versus a definitive method, whom definition remains uncertain.

[Comparison of methods for the determination of blood creatinine]. / Comparison des méthodes de dosage de la créatinine sérique.

Creatinine is the criterion the most widely used for kidney exploration, either directly or through algorithms. Up to now, it appears that methods of creatinine determination are still very heterogenous. The aim of the present study was to compare the different available methods and to evaluate their impact on the formula of predicted clearance. The study revealed that significant discrepancies can be observed depending on the methodology and analitycal principe. The results suggest that standardization of methods and comprehensive analysis of the different formula are necessary.

Thyroid testing using the Cobas Core immunoassay system. A multicentre study.

The random access immunoanalyzer Cobas Core and the Cobas Core Thyroid Assays were assessed as to their clinical usefulness in the analysis of different thyroid diseases. Four centres participated in this study measuring the following five thyroid tests per sample on the instrument: thyrotropin, free thyroxine, thyroxine, triiodothyronine and free triiodothyronine. The assessment was based on studies of precision and clinical samples. Within- and between-series precisions showed a mean CV over all assays of 4.3 and 6.1%, respectively. Comparison of the test results with clinical data demonstrated that the Cobas Core results are in accordance with diagnosed thyroid diseases. A good discrimination between normal and disease status and between untreated and treated status was found. Furthermore, 370 sera measured with Technicon Immuno-1 TSH and FT4 assays were compared to the respective Cobas Core EIAs). A good correlation between the assays was demonstrated.

[Comparative study of lipids, apoproteins and lipoproteins in patients with coronary disease and in a control population]. / Etude comparative des lipides, apoprotéines et lipoprotéines dans un groupe de sujets coronariens et dans une population témoin.

We carried out a comparative study of various lipid parameters (apo AI and B, LpAI, Lp(a) and LpBCIII) in coronary heart disease patients (19 males and 4 females, mean age 61 +/- 11 years) and in controls (18 males and 14 females, mean age 55 +/- 3 years) selected so that cholesterol and triglycerides levels be beneath 6 and 2.3 mmol/l in both populations. Apo AI and B were analysed by immunonephelometry and lipoparticles by electroimmunodiffusion. Nonparametric statistics tests were performed on account of the small numbers in both groups. Our study confirms the protective effect of Lp AI but did not show an obvious superiority of Lp AI quantification compared to apo AI. It highlights the interest of Lp(a) as an independent and additional risk factor for atherogenesis: no obvious correlation with any other lipidic parameter was demonstrated. An increase in Lp(a) beyond 0.30 g/l increases atherogenic risk 2.5 fold. We did not show any benefit of LpBCIII quantification in 'normolipemic' coronary patients. In conclusion, a discriminant analysis including the apo B/apo AI and apo B/LpAI ratios and Lp(a) allows an accurate classification of 67% of the patients.