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See detailApplication of the characteristic function to evaluate and compare analytical variability in an external quality assessment scheme for serum ethanol
Coucke, Wim; Charlier, Corinne ULg; Lambert, Willy et al

in Clinical Chemistry (2015), 61

As a cornerstone of quality management in the laboratory, External Quality Assessment (EQA) schemes are used to assess laboratory and analytical method performance. The characteristic function is used to ... [more ▼]

As a cornerstone of quality management in the laboratory, External Quality Assessment (EQA) schemes are used to assess laboratory and analytical method performance. The characteristic function is used to describe the relation between the target concentration and the EQA standard deviation, which is an essential part of the evaluation process. The characteristic function is also used to compare the variability of different analytical methods. We fitted the characteristic function to data from the Belgian External Quality Assessment program for serum ethanol. Data included results from headspace gas chromatography and the enzymatic methods of Abbott, Roche, Siemens, and Ortho-Clinical Diagnostics. We estimated the characteristic function with weighted nonlinear regression. By introducing dummy variables, we rewrote the original formula of the characteristic function to assess statistical inference for comparing the variability of the different analytical methods. The characteristic function fitted the data precisely. Comparison between methods showed that there was little difference between the estimated variability for low concentrations, and that the increase in SD with increasing target concentration was slower for Abbott and Roche than for the other methods. The characteristic function can successfully be introduced in clinical schemes, although its applicability to fit the data should always be assessed. Because of its easy parameterization, it can be used to assess differences in performance between analytical methods and to assess laboratory performance. The characteristic function also offers an alternative framework for coefficients of variation to describe variability of analytical methods. [less ▲]

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See detailDemystifying ethnic/sex differences in kidney function: is the difference in (estimating) glomerular filtration rate or in serum creatinine concentration?
Pottel, Hans; Hoste, Liesbeth; DELANAYE, Pierre ULg et al

in Clinica Chimica Acta (2012), 413(19-20), 1612-17

BACKGROUND: The recent evaluation of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation for estimating the glomerular filtration rate (GFR) in multiple ethnicities has raised the ... [more ▼]

BACKGROUND: The recent evaluation of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation for estimating the glomerular filtration rate (GFR) in multiple ethnicities has raised the question on how well this equation performs for African-American and Asian subjects. There is no doubt that serum creatinine (Scr) concentration differs between ethnicities and sexes. We show that creatinine-based equations for white populations may be inaccurate for estimating GFR in other ethnic/gender groups, especially in populations from Asia. METHODS: This study presents a mathematical analysis of the CKD-EPI-equation complemented with a literature review of median and reference values for IDMS-standardized Scr-concentrations for multiple ethnicities. RESULTS: The study shows that at equal eGFR-CKD-EPI-values, the ratio of Scr between females and males equals 0.79 and between other ethnicities/sexes and white males is constant too. From this information, it is possible to calculate mean Scr-values that correspond very well with literature values directly obtained from Scr-distributions in healthy white males and females and in black males, but the discrepancy is larger for other populations. CONCLUSIONS: Our results confirm the criticism that has been raised for using the CKD-EPI-equation for these ethnicities. An alternative eGFR-model is proposed based on a population-normalized Scr that needs further validation. [less ▲]

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