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

Establishing metrological traceability for small molecule measurands in laboratory medicine

For molecules that can be well described metrologically in the sense of the definition of measurands, and which can also be recorded analytically as individual substances, reference measurement service traceability to a metrologically sound foundation is a necessity. The establishment of traceability chains must be initiated by National Metrology Institutes (NMIs) according to applicable standards; they are at the top and leading position in this concept. If NMIs are not in the position to take up this task, alternative approaches must be sought. Traceability initiatives established by in vitro device industry or academia must meet the quality standards of NMIs. Adherence to International Organization for Standardization (ISO) procedure 15193 must be a matter of course for the establishment of reference measurement procedures (RMPs). Certified reference material (CRM) characterization must be thorough, e.g., by the application of quantitative nuclear magnetic resonance measurements and by adherence to ISO 15194. Both for RMPs and CRMs Joint Committee for Traceability in Laboratory Medicine (JCTLM) listing must be the ultimate goal. Results must be shared in a transparent manner to allow other stakeholders including NMIs to reproduce and disseminate the reference measurement procedures.

Bioelectrical, Anthropometric, and Hematological Analysis to Assess Body Fluids and Muscle Changes in Elite Cyclists during the Giro d’Italia

This study aimed to characterize and monitor the body fluid and muscle changes during the Giro d’Italia in nine elite cyclists via bioelectrical (whole-body and muscle-localized) anthropometric and hematological analysis. There were three checkpoint assessments: at the beginning, middle, and end of the race. The Wilcoxon signed-rank test was used to compare the data at baseline and follow up. The Spearman correlation was used to explore relationships between variables. Hotelling’s T2 test was used to determine bioelectrical differences in the complex vector. Bodyweight did not change during the competition, despite bioelectrical and hematological data indicating that at the first half of the race, there was a fluid gain, and in the second half a fluid loss occurred, reaching baseline values. These changes were especially prevalent in the extracellular water compartment. Significant correlations between whole-body bioelectrical vector changes and red blood cell parameter changes were reported. The muscle group most sensitive to changes were the calves. Quadriceps, hamstrings, and calves reported a PhA decrease trend during the first half of the race, and an increase during the second half. Bioelectrical impedance vector analysis appears to be sensitive enough to detect hydration and cellular integrity adaptions induced by competitions as demanding as the Giro d’Italia.

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.

Thyroid profile and LDH Isoenzymes as prognostic biomarkers for diabetic and/or obese subjects

BACKGROUND

This study aimed to evaluate the levels of thyroid hormones and lactate dehydrogenase (LDH) isoenzymes in obese and/or diabetic patients.

SUBJECTS AND METHODS

Forty male subjects categorized into four equal groups; group 1: Non obese control subjects, group 2: Subjects suffering from type 2 diabetes mellitus (T2DM), group 3: Obese subjects (BMI ≥ 30 kg/m2) and group 4: Subjects thatwere obese and had type 2 diabetes mellitus (T2DM). Liver, kidney, lipid, thyroid hormones, total LDH and LDH isoenzymes levels were determined.

RESULTS

There was a significant increase of TSH level (p<0.001) in diabetic group as compared with control group and a highly significant increase of TSH was obtained in obese and obese diabetic groups versus control and diabetic patients. LDH 2 was also highly significantly decreased in obese and obese diabetic groups versus diabetic patients. Percentage of LDH 4 was significantly decreased in both diabetic and obese groups and not significantly changed in obese diabetic patients as compared with the control group. LDH 5 percentage showed very highly significant decrease in diabetic, obese and highly significant decrease in obese diabetic groups when compared with control subjects while it was not significantly changed in obese and obese diabetic groups as compared with diabetic patients.

CONCLUSION

LDH isozymes can be used as valuable diagnostic markers for metabolic syndrome. This may help to explore the metabolic changes associated with obesity and diabetes complication and following up the complication of these abnormalities.

An update on clinical biochemical RIs of rabbits with special consideration for age, gender, and size

BACKGROUND

Literature regarding the impact of age and breed size on clinical biochemical measurands in rabbits is scarce.

OBJECTIVES

We aimed to establish clinical biochemical measurand RIs for rabbits bred and kept under standard conditions and to evaluate the impact of gender, age, and breed size on the results using a Nova CRT8 analyzer (Nova Biomedical GmbH) and an ABX Pentra 400 analyzer (ABX Horiba, Axonlab).

METHODS

Serum samples were available from 122 adult rabbits (56 males, 66 females) of 10 different breeds and crossbreds with a mean age of 264 ± 21 days. The impact of age was evaluated by sampling 48 rabbits at weaning (8 weeks of age) and when they reached adulthood.

RESULTS

Significantly higher median values were obtained for ALT, glutamate dehydrogenase (GLDH), and potassium in adult males compared with adult female rabbits. Total bilirubin, cholesterol, creatinine, and urea were significantly higher in adult females than adult males. Juvenile animals at weaning revealed significantly higher median values for ALP, cholesterol, GGT, GLDH, glucose, phosphate, and triglycerides compared with their adulthood values. In contrast, lower median albumin, ALT, chloride, creatinine, globulin, ionized calcium, magnesium, potassium, total protein, urea, and calcium-phosphate ratios were seen at the time of weaning compared with adulthood values. Significantly lower median CK, creatinine, and ALT were found in dwarf/small rabbit breeds compared with intermediate/large breeds.

CONCLUSIONS

These RIs are especially useful for rabbit production and experimental studies. Age should be considered when evaluating clinical biochemical measurands. Creatinine, CK, and ALT are affected by organ mass.

Impact of serum-clot contact time on lactate dehydrogenase and inorganic phosphorus serum levels

Objectives

The aim of this study is to determine the longest acceptable serum-clot contact time before centrifugation in lactate dehydrogenase and inorganic phosphorus analysis.

Materials and methods

The LDH and inorganic phosphorus serum levels from 103 adults were analyzed at three different storage times. The three measures were done immediately (T0), after a 2-h serum-clot contact (T2) and after a 4-h serum-clot contact (T4). A paired two-tailed Student t-test evaluated the impact of the serum-clot contact time on the serum levels. Another approach using analytical reproducibly and intra-individual variability was used. Furthermore, we have compared the mean percentage deviation to the measurement uncertainty.

Results

The LDH serum level is not significantly impacted by the three different studied serum-clot contact times.

The immediate Phosphorus serum level is not significantly different from the 2-h serum-clot contact condition. However, after a 4-h serum-clot contact, the phosphorus serum level is significantly lower than the immediate phosphorus serum level. Considering the reference change value approach, an acceptable mean variation was shown for inorganic phosphorus serum level after a 4-h serum-clot contact time. After a 4-h serum-clot contact, LDH and phosphorus mean percentage deviation are below our measurement uncertainties.

Conclusion

This study evidences that in our daily practices a 4-h serum-clot contact time for LDH and inorganic phosphorus analysis is acceptable.

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.

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.

Pediatric reference intervals determined in ambulatory and hospitalized children and juveniles

OBJECTIVES

The aim of this study was to determine reference intervals in children and juveniles with nine recently developed and widely used laboratory methods.

METHODS

More than 800 ambulatory and hospitalized individuals of the University pediatry were carefully selected according to clinical status and chemical profile in an a posteriori process over a period of two and a half years. The reference group with well-balanced gender proportions and steady age distribution between 1 day and 17 years was subdivided in five age classes. The laboratory methods were: the enzyme methods ALT, AST, LDH and GGT, all reliably reference standardized with traceability to the IFCC reference methods at 37 degrees C; ALT and AST without pyridoxal-phosphate activation; ALP as not yet approved IFCC method; the soluble transferrin receptor (sTfR) and ferritin, the latter being the only heterogeneous procedure.

RESULTS

The results confirm in most cases the typical age concentration relationship of the measured quantities documented for similar methods. In some critical cases, in particular for sTfR and ferritin, the study produces limits which differ distinctly from those earlier reported. Gender differentiation was outlined according to statistical calculations.

CONCLUSION

Proposals for reference intervals were derived from the central 95 percentile values.

Feasibility Study of the Use of Frozen Human Sera in Split-Sample Comparison of Immunoassays with Candidate Reference Measurement Procedures for Total Thyroxine and Total Triiodothyronine Measurements

Background: Diagnostic manufacturers must ensure/document metrologically traceable assays. We report on a feasibility study of a split-sample comparison for that purpose. Processed, frozen single-donation sera, assigned target values by candidate reference measurement procedures (cRMPs), were used with immunoassays for total thyroxine (TT4) and triiodothyronine (TT3) as models.

Methods: Two serum panels were quantified for TT4 and TT3 with validated cRMPs and measured in parallel with at least 14 immunoassays. The results were interpreted in terms of traceability of calibration (trueness) and of the individual measurement result (accuracy) by linear regression analysis and graphical representation against specifications. The commutability of the sera was investigated by parallel analysis of TT4 in freshly collected but nonfiltered specimens.

Results: The TT4 (TT3) concentrations in the sera (according to the cRMPs) were 64–269 nmol/L (0.88–13.7 nmol/L). The method comparison showed that for TT4, on average, the immunoassays produced results in agreement with the cRMPs, whereas for TT3, results were typically higher. It also demonstrated a considerable between-assay divergence in traceability of calibration and accuracy. The evidence of noncommutability of the sera attributable to processing, however, indicates that the interpretation should be treated with caution.

Conclusions: Frozen sera can be used for documenting/validating traceability of total thyroid measurements. The way in which the sera are processed may jeopardize commutability, however, and therefore requires in-depth investigation.

Standardization in laboratory medicine: new challenges

The primary goal of Laboratory Medicine is to provide information that is useful to assist medical decision-making and permits optimal health care. This type of information should be independently obtained of the measurement test kits and instruments, and also of the laboratory where the procedure is carried out. It is therefore important to achieve a level of comparability of laboratory results among the many measurement procedures available so that results are harmonized and interchangeable over space and time. The standardization of measurements is therefore of high priority. In recent years, numerous efforts have been made at the international level under the auspices of the IFCC and other organizations to standardize measurement results for many important analytes, e.g. enzymes, cardiac proteins, etc. The aim of this review is to discuss some concepts related to the achievement of standardization by the implementation of a metrologically correct measurement system, providing some examples on how these concepts can be applied in Laboratory Medicine.

Metrologic Traceability of Total Thyroxine Measurements in Human Serum: Efforts to Establish a Network of Reference Measurement Laboratories

Background: Assuring/demonstrating metrologic traceability of in vitro diagnostics necessitates the availability of measurand-specific reference measurement systems (RMSs) and the possibility for industry to work with competent reference measurement laboratories (RMLs). Here we report the results of a European project to investigate the feasibility of developing a RMS for serum total thyroxine.

Methods: Four candidate RMLs (cRMLs) developed/implemented variants of a candidate reference measurement procedure (cRMP) based on isotope dilution–liquid chromatography–mass spectrometry. The sole constraint implemented was calibration with a common thyroxine primary calibrator. The RMPs were externally validated and assessed for comparability in round-robin trials using common samples, i.e., 5 lyophilized and 33 frozen native sera. At the same time, the performance of the cRMLs organized in a network was assessed. For uniform external quality assessment, common performance specifications were agreed on.

Results: All cRMLs performed the cRMPs with fulfillment of the predefined specifications: total and between-laboratory CVs ≤2.0% and 2.5%, respectively, and a systematic deviation ≤0.9%, estimated with a target assigned from the mean of means obtained by the cRMLs. The mean expanded uncertainty for value assignment to the native sera was 2.1%.

Conclusions: A network of cRMLs, with externally conformed competence to properly perform RMPs, has been established. Performance specifications were defined and will form the basis for admittance of new network members. A serum panel, successfully targeted during the validation process, is available for split-sample measurements with commercial routine measurement procedures. The model can now be used for other measurands for which traceability to the Système International d’Unités is needed.

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°C. Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of γ-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase according to IFCC Reference Procedures at 37°C

This paper is the seventh 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. A document describing the determination of preliminary reference values is also in preparation. The certification of the catalytic activity concentrations as determined by the recently elaborated IFCC primary reference methods at 37 degrees C of four enzyme preparations, namely IRMM/IFCC 452 (gamma-glutamyltransferase), IRMM/IFCC 453 (lactate dehydrogenase 1), IRMM/IFCC 454 (alanine aminotransferase) and IRMM/IFCC 455 (creatine kinase) is described. Homogeneity data were derived from previous results. Stability was assessed using recently obtained data as well as data from previous stability studies. The collaborative study for value assignment was performed under a strict quality control scheme to ensure traceability to the primary reference method. Uncertainty of the materials was assessed in compliance with the Guide to the Expression of Uncertainty in Measurement. The certified values obtained at 37 degrees C are 1.90 microkat/l +/- 0.04 microkat/l (114.1 U/l +/- 2.4 U/l), for gamma-glutamyltransferase, 8.37 microkat/l +/- 0.12 microkat/l (502 U/l +/- 7 U/l), for lactate dehydrogenase 1, 3.09 microkat/l +/- 0.07 microkat/l (186 U/l +/- 4 U/l), for alanine aminotransferase and 1.68 microkat/l +/- 0.07 microkat/l (101 U/l +/- 4 U/l), for creatine kinase. The materials are intended for internal quality control as well as for the evaluation of test systems as required by recent European Union legislation. Furthermore, the materials can be used to transfer accuracy from a reference method to a routine procedure provided the procedures exhibit the same analytical specificity and the certified materials are commutable.