Biological variation of metabolic cardiovascular risk factors in haemodialysis patients and healthy individuals.

BACKGROUND: Maintenance haemodialysis (HD) is associated with a very high cardiovascular risk and the assessment of metabolic cardiovascular risk factors is essential for an adequate diagnosis and management. The aim of the study has been to estimate the biological variation (BV) of serum lipids, calcium, inorganic phosphorus, 25-OH vitamin D, C-reactive protein and plasma intact parathyroid hormone (PTHi) and total homocysteine, to evaluate whether HD alter the homeostatic set-point of these magnitudes. METHODS: Blood samples were collected from 18 HD patients in steady-state conditions, one per month during 6 months, and from 11 healthy volunteers at weekly intervals over 5 weeks. BV data were derived using CV-ANOVA. RESULTS: Within-subject coefficients of variation (CVI) and derived reference change values (RCV) estimated in HD patients were significantly higher than in healthy individuals for calcium (CVI =3.8% vs. 2.3%) (RCV =12.6% vs. 7.6%), inorganic phosphorus (13.1% vs. 8.0%) (RCV =38.7% vs. 30.1%) and PTHi (20.3% vs. 11.3%) (RCV =57.5% vs. 34.0%). CONCLUSIONS: For calcium, inorganic phosphorus and PTHi, RCV derived from advanced disease-specific BV data is recommended for the management of bone-mineral disturbances in HD patients. For the rest of cardiovascular risk factors, the use of RCV derived from healthy individuals could be appropriate.

Critical appraisal and meta-analysis of biological variation studies on glycosylated albumin, glucose and HbA1c.

Objectives: Numerous biological variation (BV) studies have been performed over the years, but the quality of these studies vary. The objectives of this study were to perform a systematic review and critical appraisal of BV studies on glycosylated albumin and to deliver updated BV estimates for glucose and HbA1c, including recently published high-quality studies such as the European Biological Variation study (EuBIVAS). Methods: Systematic literature searches were performed to identify BV studies. Nine publications not included in a previous review were identified; four for glycosylated albumin, three for glucose, and three for HbA1c. Relevant studies were appraised by the Biological Variation Data Critical Appraisal Checklist (BIVAC). Global BV estimates were derived by meta-analysis of BIVAC-compliant studies in healthy subjects with similar study design. Results: One study received BIVAC grade A, 2B, and 6C. In most cases, the C-grade was associated with deficiencies in statistical analysis. BV estimates for glycosylated albumin were: CVI=1.4% (1.2-2.1) and CVG=5.7% (4.7-10.6), whereas estimates for HbA1c, CVI=1.2% (0.3-2.5), CVG=5.4% (3.3-7.3), and glucose, CVI=5.0% (4.1-12.0), CVG=8.1% (2.7-10.8) did not differ from previously published global estimates. Conclusions: The critical appraisal and rating of BV studies according to their methodological quality, followed by a meta-analysis, generate robust, and reliable BV estimates. This study delivers updated and evidence-based BV estimates for glycosylated albumin, glucose and HbA1c.

Impact of implementing a category 1 external quality assurance scheme for monitoring harmonization of clinical laboratories in Spain.

Background: The objective of the present study was to examine the evolution of the analytical performance specifications (APS) used in External Quality Assurance (EQA) schemes, as well as the efficacy of a category 1 EQA scheme in monitoring the harmonization of clinical laboratory results in Spain. Methods: A review of the literature on the types of quality specifications used in schemes in other countries and their evolution was performed. In addition, a comparative analysis of the potential impact that different APS from eight countries had on clinical decision-making was made based on three measurands: sodium, thyroid-stimulating hormone (TSH), and activated partial thromboplastin time (aPTT). Results: Harmonization of analytical methods was demonstrated by assessing whether average results deviated from the certified reference value of control materials within the APS derived from biological variation (BV). The APS used in EQA have evolved from state-of-the-art models to BV. Poor clinical decision-making would occur if the results accepted by some APS were applied. Conclusions: In Spain, only 2 of the 18 measurands studied are considered to be well harmonized. Closer collaboration between laboratories and analytical system providers would be required to resolve discrepancies.

Spanish society of laboratory medicine external quality assurance programmes: evolution of the analytical performance of clinical laboratories over 30 years and comparison with other programmes.

The purpose of this study is to understand the evolution of the analytical performance of the laboratories participating in the Spanish society of laboratory medicine (SEQCML) external quality assurance (EQA) programmes during its 30 years of operation and to compare it with the performance of other EQA programmes to establish whether the results are similar. The results obtained during this period are evaluated by applying the biological variability (BV) and state of the art-derived quality specifications. In addition, the results are compared with those obtained by other EQA programme organisations. It is noted that the laboratories participating in the EQA-SEQCML programmes have improved their performance over 30 years of experience and that the specifications derived from biological variation are achievable. It is difficult to compare EQA programmes, due to lack of accessibility and the differences in the design of these programmes (control materials, calculations used and analytical specifications established). The data from this study show that for some biological magnitudes the results obtained by the programmes are not yet harmonised, although efforts are being made to achieve this. Organisers of EQA programmes should also join the harmonisation effort by providing information on their results to enable comparison.

Standardization in laboratory medicine: Two years' experience from category 1 EQA programs in Spain.

INTRODUCTION: Standardization is the ability to obtain interchangeable results leading to same medical interpretation. External quality assessment (EQA) is the main support of the on-going harmonization initiatives. Aim of study was to evaluate results obtained from two years category 1 EQA program experience in Spain and determine the impact of applying this type of EQA program on the analytical standardization. MATERIALS AND METHODS: According to the analytical method, traceability and instrument different groups were established which results were evaluated by calculating mean, coefficient of variation and percent of deviation to the reference value. Analytical performance specifications used to the results' evaluation were derived from biological variation for bias and from the inter-laboratory coefficients of variation found in a previous pilot study. RESULTS: Only creatinine measured by enzymatic methods gave excellent results, although few laboratories used this method. Creatine kinase and GGT gave good precision and bias in all, but one instrument studied. For the remaining analytes (ALT, ALP, AST, bilirubin, calcium, chloride, glucose, magnesium, potassium, sodium, total protein and urate) some improvement is still necessary to achieve satisfactory standardization in our setting. CONCLUSIONS: The two years of category 1 EQA program experience in Spain have manifested a lack of standardization of 17 most frequent biochemistry tests used in our laboratories. The impact of the information obtained on the lack of standardization is to recommend abandoning methods such as ALT, AST without exogenous pyridoxal phosphate, Jaffe method for creatinine, and do not use non-commutable calibrators, such as aqueous solutions for calcium and sodium.

The Biological Variation Data Critical Appraisal Checklist: A Standard for Evaluating Studies on Biological Variation.

BACKGROUND: Concern has been raised about the quality of available biological variation (BV) estimates and the effect of their application in clinical practice. A European Federation of Clinical Chemistry and Laboratory Medicine Task and Finish Group has addressed this issue. The aim of this report is to (a) describe the Biological Variation Data Critical Appraisal Checklist (BIVAC), which verifies whether publications have included all essential elements that may impact the veracity of associated BV estimates, (b) use the BIVAC to critically appraise existing BV publications on enzymes, lipids, kidney, and diabetes-related measurands, and (c) apply metaanalysis to deliver a global within-subject BV (CVI) estimate for alanine aminotransferase (ALT). METHODS: In the BIVAC, publications were rated as A, B, C, or D, indicating descending compliance for 14 BIVAC quality items, focusing on study design, methodology, and statistical handling. A D grade indicated that associated BV estimates should not be applied in clinical practice. Systematic searches were applied to identify BV studies for 28 different measurands. RESULTS: In total, 128 publications were identified, providing 935 different BV estimates. Nine percent achieved D scores. Outlier analysis and variance homogeneity testing were scored as C in >60% of 847 cases. Metaanalysis delivered a CVI estimate for ALT of 15.4%. CONCLUSIONS: Application of BIVAC to BV publications identified deficiencies in required study detail and delivery, especially for statistical analysis. Those deficiencies impact the veracity of BV estimates. BV data from BIVAC-compliant studies can be combined to deliver robust global estimates for safe clinical application.

Category 1 external quality assessment program for serum creatinine.

BACKGROUND: The Commission of Analytical Quality and the Committee of External Quality Programs of Spanish Society of Laboratory Medicine (SEQC) in collaboration with the Dutch Foundation for the Quality organized the first national category 1 External Quality Assessment Programs (EQAP) pilot study. The aim is to evaluate the standardization of serum creatinine measurements in the Spanish laboratories through a category 1 external quality assurance program with commutable material and reference method assigned values. METHODS: A total of 87 Spanish laboratories were involved in this program in 2015. Each day a sample control was measured by duplicate during 6 consecutive days. Percentage deviations and coefficients of variation obtained were compared with quality specifications derived from biological variation. RESULTS: A total of 1044 creatinine results were obtained. Laboratories were coded in 11 different method-traceability combinations. Only enzymatic methods get all results within the acceptability limits. DISCUSSION: To participate in a category 1 EQAP is a valuable tool to assess the standardization degree in our country; a big effort should be made to promote laboratories to change their procedures and to use enzymatic creatinine methods, in order to achieve a satisfactory standardization degree for this important analyte.

Biologic Variation Approach to Daily Laboratory.

Biological variation gives valuable information about how the living organism regulates its constituents within and between subjects; this information on the behavior of body components allows us to derive consequences concerning reference populations and intervals. With a more pragmatic approach biological variation has three uses: setting the appropriate analytical performance specification for each analyte to limit the amount of error that laboratory could introduce in its measurements, to help distinguish health from disease, and to implement internal quality control with the automatic verification of results.

Biological variation of cardiac troponin T in patients with end-stage renal disease and in healthy individuals.

BACKGROUND: Serum cardiac troponin T concentrations are important predictors of cardiovascular and all-cause mortality in end-stage renal disease. In patients with end-stage renal disease, assessment of serial results is essential to distinguish between a cardiovascular event and chronic elevation. We employed a high-sensitivity serum cardiac troponin T assay to evaluate the long-term biological variation in end-stage renal disease patients and in healthy individuals; these biological variation data were used to define the reference change value and the analytical goals. METHODS: Serum samples were collected from 18 end-stage renal disease patients in steady-state conditions, one per month for 6 months, and from 11 healthy volunteers at weekly intervals over 5 weeks. Biological variation data were derived using analysis of variance. RESULTS: Baseline serum cardiac troponin T concentrations in end-stage renal disease patients were above the 99th percentile of the healthy population and increased with duration of haemodialysis. For end-stage renal disease patients, within-subject (CVI) and between-subject (CVG) coefficients of variation were 14.7 and 77.8%, respectively, whereas these were 5.9 and 30.4%, respectively, for healthy individuals. The derived two-tailed and one-tailed reference change values were 44.1 and 37.1%, respectively, for end-stage renal disease patients, and 21.6 and 18.2% for healthy subjects. CONCLUSIONS: For appropriate clinical management of end-stage renal disease patients in the context of a cardiovascular event, regular monitoring of serum cardiac troponin T concentrations could be important in order to allow future comparison through reference change value. Biological variation data in end-stage renal disease patients were significantly higher than for healthy individuals; therefore, the use of proper reference change value data is recommended. Moreover, the observed CVI values provide demanding imprecision goals for current technology.

Biological variation of free plasma amino acids in healthy individuals.

BACKGROUND: Biological variation data for free plasma amino acids are lacking from the more comprehensive databases. Therefore, we determined the intra- and inter-individual components of variation in healthy subjects. These data were used to define desirable goals for imprecision, bias and total error, indices of individuality and reference change values. METHODS: Plasma samples were collected from 11 volunteers at weekly intervals over 5 weeks. Free plasma amino acids were analyzed by reversed-phase HPLC and analytical and biological variation data were derived using ANOVA. RESULTS: Intra-individual coefficients of variation ranged from 9.5% to 46.4%, with lower values among the essential amino acids. The mean inter-individual coefficient of variation was 46.6% and was higher than intra-individual values for all amino acids. Thus, indices of individuality were below 0.8. Reference change values ranged from 30.9% to 128.4% and total error values ranged from 15.2% to 61.0%. CONCLUSIONS: Plasma amino acids exhibit relatively low intra-individual coefficients of variation, with essential amino acids showing tighter homeostatic control. Analytical quality goals can be reasonably achieved with current methods. Reference intervals are of limited value in the detection of unusual results in an individual. Therefore, comparison of serial results by means of the reference change values is recommended.