Total haemoglobin - a reference measuring system for improvement of standardisation.

Background Total haemoglobin (Hb) concentration in blood belongs to the most requested measurands, and the HiCN method (hemiglobincyanide) is accepted as a reference. Although the reaction principle is clearly characterised, measurement conditions and settings are not consistently defined, some of them influencing the results. An improvement of standardisation is the object. Methods After method optimization, measurement results between different calibration laboratories (CL) were compared with each other and also with results of the National Metrology Institute of Germany (PTB), with target values of certified reference material, within the RELA scheme, and to >1500 results from routine laboratories. Results Overall deviations between three CLs were ≤0.5% (n = 24 samples) in a measurement range of 20 g/L to 300 g/L. A CV of 0.4% was determined in pooled blood (1 year long-term imprecision, 99.0%-101.1% recovery of the mean). For selected measurements (n = 4 samples) the PTB participated without significant differences to three CLs, and no significant differences were observed comparing CLs to certified values of reference materials. The expanded measurement uncertainty (probability 95%) was estimated as 1.1%. Conclusions A reference measuring system, comprising measuring instruments and other devices, including reagents and supply, to generate reference measurement values for total Hb concentration of high accuracy and low measurement uncertainty is presented. Measurement parameters are investigated and defined. The reference measuring system is ready to offer service to EQA providers and to the IVD industry for certifying control materials or calibrators.

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.

External Quality Assessment Scheme for reference laboratories - review of 8 years' experience.

We describe an External Quality Assessment Scheme (EQAS) intended for reference (calibration) laboratories in laboratory medicine and supervised by the Scientific Division of the International Federation of Clinical Chemistry and Laboratory Medicine and the responsible Committee on Traceability in Laboratory Medicine. The official EQAS website, RELA (www.dgkl-rfb.de:81), is open to interested parties. Information on all requirements for participation and results of surveys are published annually. As an additional feature, the identity of every participant in relation to the respective results is disclosed. The results of various groups of measurands (metabolites and substrates, enzymes, electrolytes, glycated hemoglobins, proteins, hormones, thyroid hormones, therapeutic drugs) are discussed in detail. The RELA system supports reference measurement laboratories preparing for accreditation according to ISO 17025 and ISO 15195. Participation in a scheme such as RELA is one of the requirements for listing of the services of a calibration laboratory by the Joint Committee on Traceability in Laboratory Medicine.

IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 °C. Part 9: reference procedure for the measurement of catalytic concentration of alkaline phosphatase International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Scientific Division, Committee on Reference Systems of Enzymes (C-RSE) (1)).

Abstract This paper is the ninth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 °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 γ-glutamyltransferase; Part 7. Certification of four reference materials for the determination of enzymatic activity of γ-glutamyltransferase, lactate dehydrogenase, alanine aminotransferase and creatine kinase at 37 °C; Part 8. Reference procedure for the measurement of catalytic concentration of α-amylase. The procedure described here is derived from the previously described 30 °C IFCC reference method. Differences are tabulated and commented on in Appendix 1.

Traceability of values for catalytic activity concentration of enzymes: a Certified Reference Material for aspartate transaminase.

BACKGROUND: A new reference material for the liver enzyme aspartate transaminase (AST) (L-aspartate: 2-oxoglutarate-aminotransferase, EC 2.6.1.1), also called aspartate aminotransferase (ASAT), has been developed under the code ERM-AD457/IFCC. This certified reference material (CRM) for AST has been produced from a human type recombinant AST expressed in Escherichia coli and a buffer containing bovine serum albumin, and has been lyophilised. METHODS: The homogeneity and the stability of the material have been tested and the catalytic activity concentration has been characterised by 12 laboratories using the reference procedure for AST at 37 degrees C from the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). RESULTS: The certified catalytic activity concentration and certified uncertainty of AST in the reconstituted material are (1.74+/-0.05) microkat/L or (104.6+/-2.7) U/L (with a coverage factor k=2; 95% confidence interval). CONCLUSIONS: Both the certified value and uncertainty are traceable to the International System of Units (SI). The material is aiming to control the IFCC reference procedure for AST at 37 degrees C, which will then be used to assign values to calibrants and control materials. The present paper highlights the scientific challenges and innovations which were encountered during the development of this new CRM.

IFCC reference procedures for measurement of the catalytic concentrations of enzymes: corrigendum, notes and useful advice. International Federation of Clinical Chemistry and Laboratory Medicine (IFCC)--IFCC Scientific Division.

The primary reference measurement procedures (PRMPs) for the international standardization of catalytic concentration measurements of alpha-amylase, alanine aminotransferase, aspartate aminotransferase (AST), creatine kinase (CK), gamma-glutamyltransferase and lactate dehydrogenase have been performed in reference laboratories for several years. The IFCC Committee on Reference Systems for Enzymes and two reference laboratories, with official accreditation for the PRMPs, have collected useful information on some of the steps of the reference procedures that require special attention. This document comprises errata corrige for minor mistakes in published PRMPs for AST and CK. Several notes on the PRMPs are emphasized. This includes details that are very important for improved standardization, and general suggestions for reducing measurement uncertainty.

Standardization in clinical enzymology: a challenge for the theory of metrological traceability.

The goal of standardization for measurement of the catalytic concentration of enzymes is to achieve comparable results in human samples, independent of the reagent kits, instruments, and laboratory where the assay is performed. To pursue this objective, the IFCC has established reference systems for the most important clinical enzymes. These systems are based on the following requirements: a) reference methods, well described and evaluated extensively; b) suitable reference materials; and c) reference laboratories operating in a highly controlled manner. When these reference systems are used appropriately, the diagnostic industry can assign traceable values to commercial calibrators. Clinical laboratories that use procedures with validated calibrators to measure human specimens can now obtain values that are traceable to higher-order reference procedures. These reference systems constitute the structure of the traceability chain to which the routine methods can be linked via an appropriate calibration process, provided that they have a comparable specificity (i.e., they are measuring the same catalytic quantity).

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.

Quantitative urinary proteome analysis for biomarker evaluation in chronic kidney disease.

A limitation of proteomic methods with respect to their clinical applicability is the lack of possibilities to directly deduce the amount of a protein or peptide from a particular mass spectrometry (MS) spectrum. For quantification of chronic kidney disease (CKD)-specific urinary polypeptides in capillary electrophoresis coupled with mass spectrometry (CE-MS), we compared signal intensity calibration methods based on either urinary creatinine or stable isotope labeled synthetic marker analogues (absolute quantification) with those based on ion counting using highly abundant collagen fragments as nonmarker references (relative quantification). Our results indicate that relative quantification of biomarker excretion based on ion counts in reference to endogenous "housekeeping" peptides is sufficient for the determination of urinary polypeptide levels. The calculation of absolute concentrations via exogenous stable isotope-labeled peptide standards is of no additional benefit.

A plea for intra-laboratory reference limits. Part 2. A bimodal retrospective concept for determining reference limits from intra-laboratory databases demonstrated by catalytic activity concentrations of enzymes.

BACKGROUND: The current recommendations for establishing intra-laboratory reference limits (RLs) cannot be fulfilled by most laboratories because of the expense involved. In the current study, a bimodal method was developed to derive RLs from data stored in a laboratory information system without any assumption concerning the distribution of the diseased subgroup. METHODS: A smoothed kernel density function (D(mix)) was estimated for the distribution of combined data for non-diseased and diseased adult subjects. It was assumed that the "central" part of the distribution represents the non-diseased population, which was defined and used to estimate a Gaussian distribution of either the original values or Box-Cox transformed data. This normal distribution was now considered the distribution of the non-diseased subgroup (D(nd)). Percentiles were calculated to obtain retrospective RLs. The density function of the diseased subgroup (D(d)) was calculated by subtracting the non-diseased density function from D(mix) (D(d)=D(mix)-D(nd)). The intersection point of the D(nd) and D(d) curves identified the RL with the highest diagnostic efficiency. RESULTS: The model was applied to catalytic activity concentrations of several enzymes with data from different laboratories. The RLs obtained were similar to recently published consensus values. Differences between laboratories were small but significant. Gender stratification was necessary for alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutymaltransferse (gamma-GT), not significant for lipase and amylase and inconsistent among the laboratories for alkaline phosphatase (AP) and lactate dehydrogenase (LDH). Age stratification was only tested for two groups (18-49 and >or=50 years) and was significant for AST (females only), gamma-GT and lipase, not significant for amylase and inconsistent for AP, LDH and ALT. For gamma-GT, further stratification for age in decades was necessary for males. Creatine kinase MB (CK-MB) values were not stratified owing to the low number of data available. CONCLUSIONS: Retrospective RLs derived from intra-laboratory data pools for the catalytic activity concentration of enzymes using a modified procedure plausibly agreed with published consensus values. However, most RLs varied significantly among laboratories, thus supporting the "old" plea for intra-laboratory RLs.

Accreditation of medical laboratories in the European Union.

BACKGROUND: Using a questionnaire, the EC4 (European Communities Confederation of Clinical Chemistry and Laboratory Medicine) has collated an inventory of the accreditation procedures for medical laboratories in the EU. RESULTS AND DISCUSSION: Accreditation of medical laboratories in the countries of the EU is mostly carried out in cooperation with national accreditation bodies. These national accreditation bodies work together in a regional cooperation, the European Cooperation for Accreditation (EA). Professionals are trained to become assessors and play a prominent role in the accreditation process. The extent of the training is diverse, but assessors are kept informed and up-to-date by annual meetings. The frequency of assessments and surveillance visits differs from country to country and ranges from 1 to 4 years. More harmonisation is needed in this respect, based on a frequency that can be pragmatically handled by laboratory professionals. In the majority of EA bodies, accreditation is carried out on a test-by-test basis. Many professionals would prefer accreditation of the entire service provided within the actual field of testing (i.e., haematology, immunology, etc.), with accreditation granted if the majority of tests offered within a service field fulfil the requirements of the ISO 15189 standard. The scope of accreditation is a major point of discussions between the EC4 Working Group on Accreditation and representatives of accreditation bodies in the EA Medical Laboratory Committee.

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.

Evaluation and quality assessment of glucose concentration measurement in blood by point-of-care testing devices.

BACKGROUND: In this study the analytical performance of eight glucose point-of-care testing (POCT) devices was evaluated. For this purpose, POCT measurement of glucose in heparinized blood collected from patients was paralleled by determination of the glucose concentration in the respective plasma by an analyzer (Hitachi 917) in the central laboratory, providing traceable results. METHODS: Trueness of POCT measurements was studied by comparing the plasma POCT values (mean of five measurements) with the results from the traceable measurement procedure (TMP). RESULTS: The percentage of POCT results within +/-6% of the TMP mean value ranged from 24% to 50%, depending on the POCT device. Within the reference interval of plasma glucose (4.4-6.0 mmol/L), up to 67% of the POCT values were lower than 4.4 mmol/L, leading to a false diagnosis of hypoglycemia. In the hypoglycemic range (<4.4 mmol/L) up to 29% of the POCT analyses were false normoglycemic. CONCLUSIONS: In conclusion, this study shows an insufficient trueness of glucose measurements by POCT devices in the normo- and hypoglycemic range. To improve quality assessment, sample splitting and simultaneous measurement of blood glucose concentration every 4 weeks by POCT devices and of plasma glucose concentration by a reliable TMP is recommended.

Trueness verification and traceability assessment of results from commercial systems for measurement of six enzyme activities in serum: an international study in the EC4 framework of the Calibration 2000 project.

BACKGROUND: The in vitro diagnostics directive of the European Union requires traceability to higher order reference measurement procedures and materials for analytes in assuring the result trueness and comparability of laboratory measurements. Manufacturers must ensure that the systems they market are calibrated against available reference systems. Validation of metrologically traceable calibrations is, however, required. METHODS: A commutable serum-based material was analyzed in three reference laboratories and target values for six enzymes (ALT, AST, CK, GGT, LD, amylase) were assigned using IFCC reference measurement procedures. 70 laboratories in Germany, Italy, and The Netherlands measured the same enzymes in the material using procedures from six commercial companies. A system for maximum allowable error was developed from the biological variation model and the results of the various procedures were tested on their compliance to trueness and between-laboratory and within-laboratory variations relative to the maximum allowable. RESULTS: For ALT results were relatively good. >95% of laboratories using systems from Dade, Olympus, Ortho and Roche are expected to comply traceability within the biologically derived limits, and 94% respectively 89% from Abbott and Beckman. For AST and GGT only Dade respectively Olympus fully complied. For CK all companies showed significant bias. Nevertheless >95% of laboratories applying Abbott, Beckman and Roche systems will comply. Finally, LD and amylase measurements require significant improvement. Some manufacturers continue to sell on the European market assays giving results which are not traceable to the internationally accepted reference systems. CONCLUSIONS: The traceability of enzyme measurements obtained with routine procedures to internationally accepted IFCC reference systems is not yet satisfactorily accomplished in clinical practice.

Multicenter evaluation of a new immunoassay for procalcitonin measurement on the Kryptor System.

We compared the manually performed LUMItest procalcitonin (PCT) assay with the newly developed fully mechanized Kryptor PCT assay and determined the essential assay characteristics of this assay. The new Kryptor PCT assay was evaluated according to modified NCCLS EP-10/EP-6 protocols in five different laboratories. Samples from 696 patients were assayed using the original LUMItest PCT assay and the new Kryptor PCT assay. Possible interference by hemoglobin, triglycerides and bilirubin was evaluated by spiking patient plasma with the appropriate substances. The functional assay sensitivity (FAS) was determined by analyzing samples with low PCT concentrations. The FAS of the new Kryptor PCT assay was 0.04 ng/ml and the imprecision within- and between-series below 5% and below 10%, respectively. Within the smallest range of determination, from 0.3 ng/ml to 50 ng/ml, common to the LUMItest PCT assay (x) and the Kryptor PCT assay (y) the values correlated well: y=0.64+0.94x, s.xy=2.78 ng/ml. The performance characteristics of the Kryptor PCT assay are fully compatible with the intended clinical use. The assay allows determination of PCT in a turnaround time (TAT) of about 20 minutes and thus is adequate for STAT analyses.

New IFCC reference procedures for the determination of catalytic activity concentrations of five enzymes in serum: preliminary upper reference limits obtained in hospitalized subjects.

Consensus among clinical chemists has dictated a change in reference temperature for enzyme catalytic concentrations from 30 to 37 degrees C. Consequently, International Federation of Clinical Chemistry (IFCC) reference procedures have been redefined at the latter temperature. Acceptance in practice of these new procedures requires well-established reference values and clinical decision limits, but the establishment of reference values is complex. Therefore, as a provisional approach and to facilitate early application of the new IFCC procedures, we report our experience gained with them in the transfer of values from the consensus methods used hitherto in Germany to the new procedures. The preliminary upper reference limits were determined for catalytic activity concentrations of the enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine kinase (CK), gamma-glutamyltransferase (gamma-GT) and lactate dehydrogenase (LDH) in human sera. Since enzyme measurements are almost always made on sera from non-ambulant subjects, we have used hospital patients aged 17 years and older as the subjects of our study. The catalytic activity concentrations obtained by measurements with the German consensus methods for the respective enzyme were chosen in combination with additional enzymes of similar diagnostic relevance to classify patients' samples as part of the respective reference collective. Measurements for the determination of the upper reference limits were performed manually by use of the primary reference procedures at the measurement temperature 37 degrees C according to IFCC, and also by employing mechanized measurements adapted to the reference procedures. The upper reference limits were calculated as the 97.5th percentile of the reference collectives and determined separately for women and men: ALT: 34 U/l (female) and 45 U/l (male); AST: 31 U/l (female) and 35 U/l (male); CK: 145 U/l (female) and 171 U/l (male); gamma-GT: 38 U/l (female) and 55 U/l (male); LDH: 247 U/l (female) and 248 U/l (male).

IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C. Part 1. The concept of reference procedures for the measurement of catalytic activity concentrations of enzymes.

This paper is the first in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and with the certification of reference preparations. Other parts deal with: 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 fication of Four Reference Materials for the Determination of Enzymatic Activity of y-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary reference values is also in preparation.