Reference measurement procedure for total bilirubin in serum re-evaluated and measurement uncertainty determined.

BACKGROUND: For the determination of total bilirubin in serum the candidate reference method developed by Doumas et al. has international recognition. The primary standard SRM 916a (NIST) was recommended for use as the primary reference material for calibration. Nowadays, no primary standard is anymore commercially available. Further, a description of uncertainty components was missing. METHODS: Two reference laboratories have re-investigated the candidate reference measurement procedure. Beside minor modifications, mainly the use of a molar absorption coefficient instead of calibration by use of bilirubin standard solutions has facilitated the operating, and improved the analytical performance. All relevant sources of measurement uncertainty were investigated. RESULTS: A measurement range of 5-525 µmol/L and a CV of 0.5% to 1.4% (long term imprecision) were determined. Excellent agreement was obtained comparing to Doumas procedure (r = 0.9999) and during a two laboratory comparison participating at IFCC RELA ring trials (mean deviation: 0.6%). The combined expanded measurement uncertainty (probability 95%) for bilirubin concentrations >30 µmol/L was estimated as 2.2%. CONCLUSION: A reference system for total bilirubin based on the described reference procedure shall enable metrological traceability and optimized standardization of the values obtained in clinical routine laboratories.

Procedimientos primarios de referencia de la IFCC para la medición de concentraciones de actividad catalítica de enzimas a 37 ºC: Parte 8. Procedimiento de referencia para la medición de la concentración catalítica de alfa-amilasa [alfa-Amilasa: 1,4-alfa-D-glucan 4-glucanohidrolasa (AMY), EC 3.2.1.1]

Este trabajo es el octavo de una serie dedicada a los procedimientos de referencia para la medición de las concentraciones de actividad catalítica de las enzimas a 37 ºC y a la certificación de las preparaciones de referencia. Otras partes se refieren a: Parte 1. El concepto de los procedimientos de referencia para la medición de las concentraciones de la actividad catalítica de las enzimas; Parte 2. Procedimiento de referencia para la medición de la concentración catalítica de creatina quinasa; Parte 3: Procedimiento de referencia para la medición de la concentración catalítica de lactato deshidrogenasa; Parte 4. Procedimiento de referencia para la medición de la concentración catalítica de alanin aminotransferasa; Parte 5. Procedimiento de referencia para la medición de la concentración catalítica de aspartato aminotransferasa; Parte 6. Procedimiento de referencia para la medición de la concentración catalítica de gamma-glutamiltransferasa; Parte 7. Certificación de cuatro materiales de referencia para la determinación de la actividad enzimática de gamma-glutamiltransferasa, lactato deshidrogenasa, alanin aminotransferasa y creatina quinasa a 37 ºC. El procedimiento que se describe aquí se deduce a partir del método de referencia de la IFCC a 30 ºC descrito previamente. Las diferencias se tabulan y comentan en Clin Chem Lab Med 2006; 44: 1146-55.

Interlaboratory comparison of the Doumas bilirubin reference method.

OBJECTIVES: To assess the performance of the Doumas bilirubin reference method. DESIGN AND METHODS: Ring trails using pooled patient specimens, a calibrator and human sera enriched with unconjugated bilirubin were analyzed in five laboratories using the Doumas bilirubin reference method. RESULTS: The coefficient of variation for the linear measurement range between laboratories ranged from 1-3%. CONCLUSIONS: The Doumas bilirubin reference method is robust and reproducible. Bilirubin results using this method may be used in the development of more accurate and reliable calibrators.

IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C.

This paper is the eighth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The concept of reference procedures for the measurement of catalytic activity concentrations of enzymes; Part 2. Reference procedure for the measurement of catalytic concentration of creatine kinase; Part 3. Reference procedure for the measurement of catalytic concentration of lactate dehydrogenase; Part 4. Reference procedure for the measurement of catalytic concentration of alanine aminotransferase Part 5. Reference procedure for the measurement of catalytic concentration of aspartate aminotransferase Part 6. Reference procedure for the measurement of catalytic concentration of gamma-glutamyltransferase; Part 7. Certification of four reference materials for the determination of enzymatic activity of gamma-glutamyltransferase, lactate dehydrogenase, alanine aminotransferase and creatine kinase at 37 degrees C. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on.