Compliance to specifications in an external quality assurance program: did new biological variation estimates of the European Federation of Laboratory Medicine (EFLM) affect the quality of laboratory results?

Objectives

The results of external quality assurance schemes are evaluated against specifications generally based on biological variation (BV) data. This study was carried out to determine whether new BV values affected the level of compliance to specifications. Our secondary objective was to identify the conditions that would be compromised as a result of poor analytical performance in disease associated markers.

Methods

This study was based on the results of the SEQCML External Quality Assurance scheme for the 2015-2022 period. Deviation of the individual result from the target value was estimated. Additionally, we calculated the percentage of results that met the pre-established specification.

Results

In 97 of the 133 analytes, the level of compliance was maintained in 80-90 % of the results obtained in the two study periods. In 23 analytes, the level of compliance ranged from 51 to 79 % in the two study periods. In ALT, AST and sodium, the level of compliance was ≤50 % of the results obtained in the first study period, with sodium being the only analyte that maintained this poor level of compliance in the second study period.

Conclusions

The level of compliance to specifications remained independent from the specification used (SEQCML or EFLM) for the majority of the analytes. The results for sodium ion were below the target value, which may lead to misdiagnosis of hyponatremia. Non-compensated alkaline picrate methods overestimate creatinine, which may produce false information suggestive of kidney failure.

Cumplimiento de las especificaciones en un programa de garantía externa de la calidad. ¿Han tenido impacto los nuevos estimados de variación biológica de la European Federation of Laboratory Medicine (EFLM) en la calidad de los resultados del laboratorio?

Objetivos

Los resultados de los programas de garantía externa de la calidad se evalúan frente a especificaciones generalmente basadas en los datos de variación biológica (VB). En este trabajo se pretende comprobar, por un lado, si el cumplimiento de especificaciones varía con la aplicación de nuevos valores de VB y, por otro lado, señalar qué patologías estarían comprometidas debido a una prestación analítica poco satisfactoria de sus mensurandos clave.

Métodos

El material utilizado son los resultados de los programas externos de la SEQCML desde 2015 hasta 2022. El método es estimar la desviación del resultado individual respecto al valor diana considerado y calcular el porcentaje de resultados que cumplen la especificación pre-establecida.

Resultados

En 97 de los 133 mensurandos el cumplimiento se mantiene entre el 80 y el 100 % de los resultados obtenidos en los dos períodos estudiados. En 23 mensurandos el grado de cumplimiento oscila entre el 51 y el 79 % en los dos periodos. En ALT, AST y sodio el grado de cumplimiento es igual o menor al 50 % de los resultados en el primer período, quedando en este grupo únicamente el sodio en el segundo período.

Conclusiones

Para la mayoría de los mensurandos estudiados el cumplimiento se mantiene independiente de la especificación empleada (SEQCML o EFLM). Los resultados de ion sodio están por debajo del valor diana, por lo que podrían darse casos de diagnóstico falso de hiponatremia. Los métodos de picrato alcalino no compensado sobreestiman la creatinina, pudiendo ocasionar falsa información de insuficiencia renal.

Control externo de la calidad en medicina del laboratorio. Avances y futuro

Objectivos

Un programa de control externo distribuye las mismas muestras control entre varios laboratorios y evalúa los resultados obtenidos con un criterio común. El objetivo de este trabajo es resumir la evolución de los programas externos, poner de manifiesto los progresos conseguidos y deducir consecuencias prácticas para el laboratorio participante.

Métodos

El material es una breve revisión de los diferentes tipos de programas externos utilizados a lo largo de cuarenta años. El método es el análisis crítico de las ventajas e inconvenientes de cada modelo, a la luz de nuestra experiencia.

Resultados

A mitad del siglo XX se iniciaron los programas EQA, detectándose gran discrepancia entre resultados emitidos por distintos laboratorios. Se desarrollaron EQA en muchos países y se propusieron mecanismos para armonizarlos, como: establecer especificaciones derivadas de la variación biológica, promover el uso de métodos analíticos homogéneos, usar el EQA como herramienta educacional. A partir del 2000 se hacen importantes avances: asegurar el adecuado uso clínico de las pruebas del laboratorio, utilizar material control conmutable con el espécimen humano, armonizar los distintos modelos de EQA, promover una organización de cooperación entre organizadores de programas EQA.

Conclusiones

Participar en un EQA con controles conmutables y valores asignados por método de referencia certificado permite conocer la inexactitud real de los resultados y el impacto en las muestras de pacientes. Si se participa en programas con controles no conmutables solo se conoce si la prestación del laboratorio es similar a la de otros usuarios del mismo método analítico.

External quality control in laboratory medicine. Progresses and future

Objectives

An external quality control program distributes same control samples to various laboratories and evaluates results obtained with a common criterion. The aim of this work is to summarize the evolution of various types of external programs, to point out the progresses ant to preclude practical consequences of the participant laboratories.

Content

The material consists on a brief revision of the different types of external programs that have been used for the last forty years. The method is the critical analysis of the strong and weak points of each program model, from the light of our experience. External quality assessment (EQA) programs were initiated at half the XX century, evidencing big discrepancies among laboratory results. EQA were developed in various countries and some mechanisms to harmonize them were proposed: to establish common performance specifications derived from biological variation, to use EQS as educational tool. Since the 2000 important advances were seen: to focus EQA to assure the adequate clinical use of laboratory tests, to use commutable controls, to harmonize the different EQA models, to promote a forum for co-operation and exchange of knowledge on quality-related matters for EQA organizers.

Summary and Outlook

To participate in an EQA with commutable-reference method assigned values controls allows to know the real inaccuracy of results and their impact on patient' samples. To participate in a EQA with non commutable controls allows to know whether the individual laboratory performance agrees with that from other laboratories using same analytical method.

Within-subject biological variation estimates using an indirect data mining strategy. Spanish multicenter pilot study (BiVaBiDa)

OBJECTIVES

The estimates of biological variation (BV) have traditionally been determined using direct methods, which present limitations. In response to this issue, two papers have been published addressing these limitations by employing indirect methods. Here, we present a new procedure, based on indirect methods that analyses data collected within a multicenter pilot study. Using this method, we obtain CV_I estimates and calculate confidence intervals (CI), using the EFLM-BVD CV_I estimates as gold standard for comparison.

METHODS

Data were collected over a 18-month period for 7 measurands, from 3 Spanish hospitals; inclusion criteria: patients 18-75 years with more than two determinations. For each measurand, four different strategies were carried out based on the coefficient of variation ratio (rCoeV) and based on the use of the bootstrap method (OS1, RS2 and RS3). RS2 and RS3 use symmetry reference change value (RCV) to clean database.

RESULTS

RS2 and RS3 had the best correlation for the CV_I estimates with respect to EFLM-BVD. RS2 used the symmetric RCV value without eliminating outliers, while RS3 combined RCV and outliers. When using the rCoeV and OS1 strategies, an overestimation of the CV_I value was obtained.

CONCLUSIONS

Our study presents a new strategy for obtaining robust CV_I estimates using an indirect method together with the value of symmetric RCV to select the target population. The CV_I estimates obtained show a good correlation with those published in the EFLM-BVD database. Furthermore, our strategy can resolve some of the limitations encountered when using direct methods such as calculating confidence intervals.

Impact of ultra-low temperature long-term storage on the preanalytical variability of twenty-one common biochemical analytes

OBJECTIVES

Retrospective studies frequently assume analytes long-term stability at ultra-low temperatures. However, these storage conditions, common among biobanks and research, may increase the preanalytical variability, adding a potential uncertainty to the measurements. This study is aimed to evaluate long-term storage stability of different analytes at <-70 °C and to assess its impact on the reference change value formula.

METHODS

Twenty-one analytes commonly measured in clinical laboratories were quantified in 60 serum samples. Samples were immediately aliquoted and frozen at <-70 °C, and reanalyzed after 11 ± 3.9 years of storage. A change in concentration after storage was considered relevant if the percent deviation from the baseline measurement was significant and higher than the analytical performance specifications.

RESULTS

Preanalytical variability (CV_P) due to storage, determined by the percentage deviation, showed a noticeable dispersion. Changes were relevant for alanine aminotransferase, creatinine, glucose, magnesium, potassium, sodium, total bilirubin and urate. No significant differences were found in aspartate aminotransferase, calcium, carcinoembryonic antigen, cholesterol, C-reactive protein, direct bilirubin, free thryroxine, gamma-glutamyltransferase, lactate dehydrogenase, prostate-specific antigen, triglycerides, thyrotropin, and urea. As nonnegligible, CV_P must remain included in reference change value formula, which was modified to consider whether one or two samples were frozen.

CONCLUSIONS

After long-term storage at ultra-low temperatures, there was a significant variation in some analytes that should be considered. We propose that reference change value formula should include the CV_P when analyzing samples stored in these conditions.

Critical review and meta-analysis of biological variation estimates for tumor markers

OBJECTIVES

Biological variation data (BV) can be used for different applications, but this depends on the availability of robust and relevant BV data. In this study, we aimed to summarize and appraise BV studies for tumor markers, to examine the influence of study population characteristics and concentrations on BV estimates and to discuss the applicability of BV data for tumor markers in clinical practice.

METHODS

Studies reporting BV data for tumor markers related to gastrointestinal, prostate, breast, ovarian, haematological, lung, and dermatological cancers were identified by a systematic literature search. Relevant studies were evaluated by the Biological Variation Data Critical Appraisal Checklist (BIVAC) and meta-analyses were performed for BIVAC compliant studies to deliver global estimates of within-subject (CV_I) and between-subject (CV_G) BV with 95% CI.

RESULTS

The systematic review identified 49 studies delivering results for 22 tumor markers; four papers received BIVAC grade A, 3 B, 27 C and 15 D. Out of these, 29 CV_I and 29 CV_G estimates met the criteria to be included in the meta-analysis. Robust data are lacking to conclude on the relationship between BV and different disease states and tumor marker concentrations.

CONCLUSIONS

This review identifies a lack of high-quality BV studies for many tumor markers and a need for delivery of BIVAC compliant studies, including in different, disease states and tumor marker concentrations. As of yet, the state-of-the-art may still be the most appropriate model to establish analytical performance specifications for the majority of tumor markers.

Biological variation estimates of thyroid related measurands - meta-analysis of BIVAC compliant studies

OBJECTIVES

Testing for thyroid disease constitutes a high proportion of the workloads of clinical laboratories worldwide. The setting of analytical performance specifications (APS) for testing methods and aiding clinical interpretation of test results requires biological variation (BV) data. A critical review of published BV studies of thyroid disease related measurands has therefore been undertaken and meta-analysis applied to deliver robust BV estimates.

METHODS

A systematic literature search was conducted for BV studies of thyroid related analytes. BV data from studies compliant with the Biological Variation Data Critical Appraisal Checklist (BIVAC) were subjected to meta-analysis. Global estimates of within subject variation (CV_I) enabled determination of APS (imprecision and bias), indices of individuality, and indicative estimates of reference change values.

RESULTS

The systematic review identified 17 relevant BV studies. Only one study (EuBIVAS) achieved a BIVAC grade of A. Methodological and statistical issues were the reason for B and C scores. The meta-analysis derived CV_I generally delivered lower APS for imprecision than the mean CV_A of the studies included in this systematic review.

CONCLUSIONS

Systematic review and meta-analysis of studies of BV of thyroid disease biomarkers have enabled delivery of well characterized estimates of BV for some, but not all measurands. The newly derived APS for imprecision for both free thyroxine and triiodothyronine may be considered challenging. The high degree of individuality identified for thyroid related measurands reinforces the importance of RCVs. Generation of BV data applicable to multiple scenarios may require definition using "big data" instead of the demanding experimental approach.

Should clinical laboratories adapt to the reality of chronic kidney disease in the determination of parathyroid hormone?

Objectives

The contribution of the clinical laboratory to diagnostics is increasingly important since a great deal of clinical decisions rely on laboratory test results.

Content

Parathyroid hormone (PTH) measurement presents a considerable analytical variability due to the heterogeneity of its circulating forms and the antigenic configuration of the different assays commercially available. Such variability may have an impact on pathological conditions associated with significant increases in circulating PTH, as it is the case of chronic kidney disease (CKD).

Summary

Despite the recent identification of new molecules involved in bone and mineral disorders associated with CKD, such as klotho or the fibroblastic factor 23 (FGF23), nephrologists still base their clinical decisions on PTH concentrations. The problem is that unawareness of these analytical considerations may cause errors in the clinical interpretation of test results.

Outlook

This systematic review addresses these issues from the clinical laboratory perspective and proposes new approaches related to PTH method selection and result expression. These new strategies will help laboratory medicine specialists and nephrologist better determine the status of CKD patients.

Evaluación crítica y meta-análisis de estudios de variación biológica para albúmina glicosilada, glucosa y HbA1c

Objetivos

A lo largo de los años se han publicado numerosos artículos sobre variación biológica (VB) de diferente calidad. Los objetivos de este trabajo fueron realizar una revisión sistemática y una evaluación crítica de los estudios de VB para albúmina glicosilada y proporcionar datos actualizados de VB para glucosa y HbA_1c, incluyendo prestigiosos estudios recientemente publicados como el Estudio de Variación Biológica Europea (EuBIVAS).

Métodos

Se hizo una búsqueda bibliográfica sistemática para identificar estudios sobre VB, encontrándose 9 estudios no incluidos en la primera revisión: 4 para albúmina glicosilada, 3 para glucosa y 3 para HbA_1c. Se realizó una evaluación crítica de los estudios relevantes, utilizando la herramienta Biological Variation Data Critical Appraisal Checklist (BIVAC). Se obtuvieron los estimados globales de VB mediante meta-análisis de los estudios que cumplían los requisitos BIVAC, realizados en individuos sanos con estudios de diseño similar.

Resultados

Un estudio recibió el grado A, dos el B y 6 el C. en la mayoría de los casos el grado C se asoció a deficiencias en el análisis estadístico de los datos. Los estimados de VB para albúmina glicosilada fueron: CV_I = 1,4%(1,2–2,1) y CV_G = 5,7%(4,7–10,6); para HbA_1c, CV_I = 1,2%(0,3–2,5), CV_G = 5,4%(3,3–7,3) y para glucosa, CV_I = 5,0%(4,1–12,0), CV_G = 8,1%(2,7–10,8) no difirieron de los estimados globales previamente descritos.

Conclusiones

La evaluación crítica y clasificación de los estudios de VB a tenor de su calidad metodológica, seguido de un meta-análisis, genera estimados de VB robustos y fiables. Este estudio proporciona datos de VB para albúmina glicolisada, glucosa y HbA_1c actualizados y basados en la evidencia científica.

Critical appraisal and meta-analysis of biological variation estimates for kidney related analytes

Objective

Kidney markers are some of the most frequently used laboratory tests in patient care, and correct clinical decision making depends upon knowledge and correct application of biological variation (BV) data. The aim of this study was to review available BV data and to provide updated BV estimates for the following kidney markers in serum and plasma; albumin, creatinine, cystatin C, chloride, potassium, sodium and urea.

Content

Relevant studies were identified from a historical BV database as well as by systematic literature searches. Retrieved publications were appraised by the Biological Variation Data Critical Appraisal Checklist (BIVAC). Meta-analyses of BIVAC compliant studies with similar design were performed to deliver global estimates of within-subject (CVI) and between-subject (CVG) BV estimates. Out of the 61 identified papers, three received a BIVAC grade A, four grade B, 48 grade C, five grade D grade and one was not appraised as it did not report numerical BV estimates. Most studies were identified for creatinine (n=48). BV estimates derived from the meta-analysis were in general lower than previously reported estimates for all analytes except urea. For some measurands, BV estimates may be influenced by age or states of health, but further data are required.

Summary

This review provides updated global BV estimates for kidney related measurands. For all measurands except for urea, these estimates were lower than previously reported.

Outlook

For the measurands analyzed in this review, there are sufficient well-designed studies available to publish a trustworthy estimate of BV. However, for a number of newly appearing kidney markers no suitable data is available and additional studies are required.

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 HbA_1c, 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 HbA_1c. 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: CV_I=1.4% (1.2-2.1) and CV_G=5.7% (4.7-10.6), whereas estimates for HbA_1c, CV_I=1.2% (0.3-2.5), CV_G=5.4% (3.3-7.3), and glucose, CV_I=5.0% (4.1-12.0), CV_G=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 HbA_1c.

Models to estimate biological variation components and interpretation of serial results: strengths and limitations

Biological variation (BV) has multiple applications in a variety of fields of clinical laboratory. The use of BV in statistical modeling is twofold. On the one hand, some models are used for the generation of BV estimates (within- and between-subject variability). Other models are built based on BV in combination with other factors to establish ranges of normality that will help the clinician interpret serial results for the same subject. There are two types of statistical models for the calculation of BV estimates: A. Direct methods, prospective studies designed to calculate BV estimates; i. Classic model: developed by Harris and Fraser, revised by the Working Group on Biological Variation of the European Federation of Laboratory Medicine. ii. Mixed-effect models. iii. Bayesian model. B. Indirect methods, retrospective studies to derive BV estimates from large databases of results. Big data. Understanding the characteristics of these models is crucial as they determine their applicability in different settings and populations. Models for defining ranges that help in the interpretation of individual serial results include: A. Reference change value and B. Bayesian data network. In summary, this review provides an overview of the models used to define BV components and others for the follow-up of patients. These models should be exploited in the future to personalize and improve the information provided by the clinical laboratory and get the best of the resources available.

Modelos para estimar la variación biológica y la interpretación de resultados seriados: bondades y limitaciones

La variación biológica (VB) tiene múltiples aplicaciones en diversos campos del laboratorio clínico. Hay dos formas de relacionar el concepto de VB y los modelos estadísticos. Por un lado existen modelos para el cálculo de estimados de VB (intra e inter individual) y por otro, existen modelos que tienen en cuenta la VB y otros factores para la definición de rangos que ayudan a la interpretación de resultados seriados en un mismo individuo. Dentro de los modelos estadísticos dirigidos al cálculo de los estimados de VB existen dos tipos: A. Métodos directos. Estudios prospectivos, diseñados exclusivamente para el cálculo de estimados de VB: i. Modelo clásico: desarrollado por Harris y Fraser, revisado por EFLM-BVWG. ii. Modelos de efectos mixtos iii. Modelo bayesiano. B. Métodos indirectos. Estudios retrospectivos basados en extraer estimados de VB a partir de resultados que provienen de grandes bases de datos. Big-data. Ambos tipos presentan una serie de características que es importante conocer porque pueden condicionar su aplicabilidad en diferentes situaciones o poblaciones. Entre los modelos para definir rangos que ayudan a la interpretación de resultados seriados en un individuo encontramos: A. Valor de referencia del cambio (VRC). B. Red de datos bayesiana. En resumen, esta revisión pretende dar un enfoque general sobre los modelos para definir los componentes de VB así como otros para aplicarlos en el seguimiento de pacientes, que deberían ser explorados en el futuro para personalizar y mejorar la información aportada por el laboratorio clínico, aprovechando al máximo los recursos disponibles.

Systematic review and meta-analysis of within-subject and between-subject biological variation estimates of 20 haematological parameters

Background Interpretation of the complete blood count (CBC) parameters requires reliable biological variation (BV) data. The aims of this study were to appraise the quality of publications reporting BV data for CBC parameters by applying the BV Data Critical Appraisal Checklist (BIVAC) and to deliver global BV estimates based on BIVAC compliant studies. Methods Relevant publications were identified by a systematic literature search and evaluated for their compliance with the 14 BIVAC criteria, scored as A, B, C or D, indicating decreasing compliance. Global CVI and CVG estimates with 95% CI were delivered by a meta-analysis approach using data from BIVAC compliant papers (grades A-C). Results In total, 32 studies were identified; four received a BIVAC grade A, 2 B, 20 C and 6 D. Meta-analysis derived CVI and CVG estimates were generally lower or in line with those published in a historical BV database available online. Except for reticulocytes, CVI estimates of erythrocyte related parameters were below 3%, whereas platelet (except MPV and PDW) and leukocyte related parameters ranged from 5% to 15%. Conclusions A systematic review of CBC parameters has provided updated, global estimates of CVI and CVG that will be included in the newly published European Federation of Clinical Chemistry and Laboratory Medicine BV Database.

Programas de garantía externa de la calidad SEQCML. Evolución de las prestaciones analíticas de los laboratorios clínicos a lo largo de 30 años y comparación con otros programas

Objetivos

El objetivo de este estudio es conocer la evolución de la prestación analítica de los laboratorios participantes en los programas EQA de la SEQCML durante los 30 años de funcionamiento y compararla con la prestación obtenida en otros programas EQA para saber si los resultados son similares.

Métodos

Se evalúan los resultados obtenidos durante este periodo, aplicando las especificaciones de la calidad derivadas de la VB y del estado del arte. Además, se realiza una comparación con los resultados obtenidos por otras organizaciones de programas EQA.

Resultados

Se observa que los laboratorios participantes en los programas EQA-SEQCML han mejorado su prestación durante los 30 años de experiencia y que las especificaciones derivadas de la variación biológica son alcanzables. La comparación entre programas EQA es difícil, debido a: la falta de accesibilidad y a las diferencias en el diseño de estos programas (materiales control, cálculos empleados y especificaciones analíticas establecidas).

Conclusiones

Los datos de este estudio ponen de manifiesto que para algunas magnitudes biológicas los resultados obtenidos en los programas todavía no están armonizados, aunque se estan realizando esfuerzos para alcanzar la armonización. Los organizadores de programas EQA deberían sumarse al esfuerzo de armonización, facilitando la información sobre sus resultados para permitir su comparación.

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 (SEQC^ML) 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-SEQC^ML 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.

Impacto de la introducción de un programa externo de categoría 1 en la vigilancia de la estandarización entre laboratorios clínicos en España

Introducción

El objetivo de este estudio es comprobar la evolución de las especificaciones de la prestación analítica (EPA) utilizadas en programas de garantía externa de la calidad (EQA) y el papel de un programa de categoría 1 en la vigilancia de la estandarización de la prestación de los laboratorios clínicos en España.

Métodos

Se ha revisado la bibliografía sobre tipos de especificaciones de la calidad usados en programas de otros países y se ha comprobado su evolución; se ha comparado el posible impacto de distintas EPA empleadas en ocho países en la toma de decisiones clínicas con tres ejemplos de magnitudes: sodio, tirotropina (TSH) y tiempo de tromboplastina parcial activado (TTPA).

Resultados

Se ha evidenciado la estandarización entre métodos analíticos comprobando si los resultados medios se desvían respecto al valor de referencia certificado del control dentro de las EPA derivadas de la variación biológica (VB). Las EPA usadas en EQA han evolucionado desde el estado del arte hacia la VB. Si se aplican los resultados que se aceptarían con algunas EPA se podrían producir decisiones clínicas erróneas.

Conclusiónes

En España, solo 2 de las 18 magnitudes biológicas estudiadas se pueden considerar bien estandarizadas. Sería necesaria una colaboración más estrecha entre los laboratorios y proveedores de sistemas analíticos para resolver las discrepancias.

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.

A protocol for testing the stability of biochemical analytes. Technical document

Stability of a measurand in a specimen is a function of the property variation over time in specific storage conditions, which can be expressed as a stability equation, and is usually simplified to stability limits (SLs). Stability studies show differences or even inconsistent results due to the lack of standardized experimental designs and heterogeneity of the chosen specifications. Although guidelines for the validation of sample collection tubes have been published recently, the measurand stability evaluation is not addressed. This document provides an easy guideline for the development of a stability test protocol based on a two-step process. A preliminary test is proposed to evaluate the stability under laboratory habitual conditions. The loss of stability is assessed by comparing measurement values of two samples obtained from the same patient and analyzed at different time points. One of them is analyzed under optimal conditions (basal sample). The other is stored under specific stability conditions for a time set by the laboratory (test sample). Differences are expressed using percentage deviation (PD%) to facilitate comparison with specifications. When the preliminary test demonstrates instability, a comprehensive test is proposed in order to define the stability equation and to specify SLs. Several samples are collected from a set of patients. The basal sample is analyzed under optimal conditions, whereas analysis of test samples is delayed at time intervals. For each patient PD% is calculated as the difference between measurements for every test sample and its basal one and represented in a coordinate graph versus time.

Biological variation data for lipid cardiovascular risk assessment biomarkers. A systematic review applying the biological variation data critical appraisal checklist (BIVAC)

BACKGROUND

Biological variation (BV) data can be used to set analytical performance specifications (APS) for lipid assays. Poor performance will impact upon the efficacy of international guidelines for cardiovascular risk assessment (CVR) and relevant clinical decision limits. This systematic review applies the Biological Variation Data Critical Appraisal Checklist (BIVAC) to published studies of BV of CVR biomarkers enabling metanalysis of the data.

METHODS

Studies of BV of total cholesterol, HDL-cholesterol, LDL-cholesterol, triglycerides and apolipoproteins A₁ and B, retrieved using a systematic literature search, were evaluated and graded using the BIVAC. Meta-analysis of CV_I and CV_G estimates were performed utilizing weightings based upon BIVAC grades and the width of the data confidence intervals.

RESULTS

Applying the BIVAC, ten publications were graded as D, 43 as C, 5 as B and 1 as A (fully compliant). A total of 196 CV_I and 87 CV_G estimates were available for the different lipid measurands. The meta-analysis-derived BV data estimates were generally concordant with those in the online 2014 BV database.

CONCLUSIONS

Application of BIVAC identifies BV data suitable for many important applications including setting APS. Additionally, this review identifies a need for new BIVAC compliant studies to deliver BV reference data in different subpopulations.

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.

Systematic review of the biological variation data for diabetes related analytes

BACKGROUND

Objective interpretation of laboratory test results used to diagnose and monitor diabetes mellitus in part requires the application of biological variation data (BVD). The quality of published BVD has been questioned. The aim of this study was to quality assess publications reporting BVD for diabetes-related analytes using the Biological Variation Data Critical Appraisal Checklist (BIVAC); to assess whether published BVD are fit for purpose and whether the study design and population attributes influence BVD estimates and to undertake a meta-analysis of the BVD from BIVAC-assessed publications.

METHODS

Publications reporting data for glucose, HbA_1c, adiponectin, C-peptide, fructosamine, insulin like growth factor 1 (IGF-1), insulin like growth factor binding protein 3 (IGFBP-3), insulin, lactate and pyruvate were identified using a systematic literature search. These publications were assessed using the BIVAC, receiving grades A, B, C or D, where A is of highest quality. A meta-analysis of the BVD from the assessed studies utilised weightings based upon BIVAC grades and the width of the data confidence intervals to generate global BVD estimates.

RESULTS

BIVAC assessment of 47 publications delivered 1 A, 3 B, 39C and 4 D gradings. Publications relating to adiponectin, C-peptide, IGF-1, IGFBP-3, lactate and pyruvate were all assessed as grade C. Meta-analysis enabled global BV estimates for all analytes except pyruvate, lactate and fructosamine.

CONCLUSIONS

This study delivers updated and evidence-based BV estimates for diabetes-related analytes. There remains a need for delivery of new high-quality BV studies for several clinically important analytes.

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.

Experimental study showed that adding fortifier and extra-hydrolysed proteins to preterm infant mothers' milk increased osmolality

AIM

Measuring milk osmolality after adjustable fortification is clinically relevant, as values exceeding recommended safety thresholds might result in gastrointestinal consequences. The aim of this study was to evaluate the effect of four fortification levels and storage time on the osmolality of human milk.

METHODS

This was an experimental study using 71 spare samples of fresh breastmilk collected from 31 mothers of preterm infants. Osmolality was measured before and after adding commercial human milk fortifier containing dextrinomaltose and hydrolysed proteins at four different concentrations. Measurements were performed at various points during the 23 hours after fortification.

RESULTS

The mean basal osmolality of the 71 human milk samples was 296 ± 14 milliosmoles (mOsm)/kg, and these remained stable over a period of 23 hours. Just after fortification, the four fortified formulas showed higher osmolalities than the nonfortified human milk, ranging between 384 ± 14 and 486 ± 15 mOsm/kg, respectively (p < 0.01). This osmolality increased significantly from 20 minutes to 23 hours after fortification (p < 0.05).

CONCLUSION

Adding fortifier and extra-hydrolysed proteins to human preterm milk increased osmolality, and these osmolality levels also increased with time. We recommend evaluating the risk of hyperosmolality when a higher fortification level is needed, to avoid gastrointestinal problems.

Biological variation database: structure and criteria used for generation and update

BACKGROUND

Numerical data on the components of biological variation (BV) have many uses in laboratory medicine, including in the setting of analytical quality specifications, generation of reference change values and assessment of the utility of conventional reference values.

METHODS

Generation of a series of up-to-date comprehensive database of components of BV was initiated in 1997, integrating the more relevant information found in publications concerning BV. A scoring system was designed to evaluate the robustness of the data included. The database has been updated every 2 years, made available on the Internet and derived analytical quality specifications for imprecision, bias and total allowable error included in the tabulation of data.

RESULTS AND CONCLUSIONS

Our aim here is to document, in detail, the methodology we used to evaluate the reliability of the included data compiled from the published literature. To date, our approach has not been explicitly documented, although the principles have been presented at many symposia, courses and conferences.

Rationale for using data on biological variation

The aims of this study are: 1) to use the data included in the biological variation (BV) database to address the usability of BV estimates; and 2) to use different examples from the authors’ laboratories to illustrate the use and the usefulness of BV data in laboratory medicine. The BV database is an essential tool for laboratory management. Examples of application of data derived from BV are given in this paper, such as analytical performance specifications that have been included in various quality control software designed to optimize operative rules; also they have been incorporated as acceptability limits in external quality assurance reports. BV data from pathological status are of utmost interest for monitoring patients and differences between the intra-individual coefficients of variation (CV

Decreased serum selenium concentrations in patients with Parkinson's disease

Selenium is an essential component of the antioxidant enzyme glutathione peroxidase. The activity of this enzyme is reduced in the substantia nigra of patients with Parkinson's disease (PD), but the results of studies on erythrocytes are controversial. We compared the serum levels of selenium and the 24 h urinary selenium excretion (measured by hydride generation atomic absorption spectrophotometry) in 29 PD patients and 30 matched controls. Serum selenium levels were significantly lower in PD patients than in controls (34.6 ± 2.35 and 45.2 ± 3.83 μg/l, p < 0.05) while urinary excretion was similar for both groups (47.1 ± 6.25 and 45.5 ± 5.38 μg/24 h). These values were not influenced by antiparkinsonian drugs, and they did not correlate with age, age at onset and duration of the PD, scores of the Unified PD Rating Scale or the Hoehn and Yahr staging in the PD group. These results might suggest a possible role of low serum selenium levels in the risk for, or a consequence of the oxidative stress in PD.

Peripheral iron metabolism in patients with focal cerebral ischemia

To ascertain the possible role of iron as a risk factor for cerebral ischemia, we studied the serum levels of iron, transferrin and ferritin in 42 patients between the third and seventh days after a cerebral ischemic event (transient ischemic attack, reversible ischemic neurological deficit or cerebral infarction) and in 62 matched controls. The serum levels of iron did not differ significantly between cerebral ischemic patient and control groups. Serum transferrin levels were lower and ferritin higher in stroke patients than in controls. These values were not influenced by age, blood pressure, or smoking and alcohol drinking habits. These results suggest that iron stores could be related to the risk for cerebral ischemia.

Plasma levels of nitrates in patients with Parkinson's disease

It has been suggested that nitric oxide (NO) could be implicated in the neuronal degeneration of substantia nigra compacta in patients with Parkinson's disease (PD). To ascertain the possible role of NO as risk factor for PD, we studied the plasma levels of nitrate (oxidation product that provides an indirect estimation of NO), in 68 PD patients and 68 matched-controls. The plasma levels of nitrate did not differ significantly between PD patient and control groups (44.5 +/- 2.46 and 44.8 +/- 2.67 mumol/l, respectively). They were not influenced by antiparkinsonian drug and they did not correlate with age at onset, duration, scores of the Unified Parkinson's Disease Rating scales and Hoehn and Yahr staging in the PD group. These data suggest that plasma levels of nitrate are apparently unrelated to the risk for PD.

Alcoholic cognitive deterioration and nutritional deficiencies

Chronic alcoholic patients frequently exhibit a mild to moderate cognitive impairment that has been related to Wernicke-Korsakoff encephalopathy and attributed tentatively to nutritional and vitamin deficiencies. To elucidate the possible relation between alcoholic cognitive deterioration (ACD) and nutritional and vitamin deficiencies, several tests of intelligence and memory were administered to 54 chronic alcoholic patients and 30 controls. Serum levels of thiamine, folic acid, vitamins B12, A, and E, and certain nutritional indexes were determined in most of the subjects. The alcoholics scored significantly lower in intellectual and visuospatial tasks but not in verbal memory tasks. They had a lower serum level for thiamine but not of the remaining vitamins. However, the correlations between serum thiamin and cognitive performance scores were low, and according to stepwise regression analysis, duration of alcohol intake and education were the variables with predictive value for intellectual and memory test performance. These results suggest that serum thiamin deficiency is not the main pathogenetic factor related to ACD.

Serum levels of beta-carotene and other carotenoids in Parkinson's disease

To elucidate the possible role of carotenoids in the risk for developing Parkinson's disease (PD), we compared serum levels of beta-carotene, alpha-carotene and lycopene, measured by high performance liquid chromatography, of 61 PD patients using their spouses as the control group. The serum levels of these 3 carotenoids did not differ significantly between PD patients and control groups. There was no influence of antiparkinsonian therapy on serum carotenoids levels, and these did not correlate with age, age at onset, scores of the Unified Parkinson Disease Rating Scale or the Hoehn and Yahr staging in the PD group. These results show that serum carotenoids concentrations are apparently unrelated to the risk for developing PD.

Is an intestinal permeability test a valid marker for slight dietary transgressions in adolescents with coeliac disease?

Adolescents with coeliac disease often fail to adhere to a strict gluten free diet. The effectiveness of intestinal permeability to sugars as a marker of slight dietary transgressions by such adolescents was assessed. Severe dietary transgressions were excluded from the study. Subjects were divided into two groups according to whether they committed slight dietary transgressions or adhered to a strict gluten free diet. A reference group of preadolescents with coeliac disease was also included in the study. Intestinal permeability and antigliadin antibody tests were performed on all patients. The diagnostic marker of intestinal permeability was excellent in the reference group. Neither the intestinal permeability test nor antigliadin antibody tests, however, succeeded in discriminating between the two groups of adolescents considered in this study. In conclusion the intestinal permeability test is not a valid marker for slight dietary transgression in such patients.

Serum levels of zinc and copper in patients with Parkinson's disease

Several recent studies have shown decreased copper and increased zinc concentrations in the substantia nigra and increased copper concentrations in the cerebrospinal fluid of Parkinson's disease patients. To elucidate whether changes in serum levels of these trace elements may increase the risk of developing Parkinson's disease (PD), we assessed serum levels of zinc and copper by flame atomic absorption spectrophotometry, and albumin and ceruloplasmin, in 32 (Zn) and 39 PD patients (Cu), respectively, with their spouses as the control group. Serum zinc, albumin, copper and ceruloplasmin levels and the zinc/albumin and copper/ceruloplasmin ratios, did not differ significantly between the two groups and were not influenced by antiparkinsonian therapy in the PD patients. Serum zinc/albumin ratio (r = 0.43), ceruloplasmin (r = -0.36) and copper/ceruloplasmin ratio (r = 0.36) correlated significantly with age, but not with age of onset, duration of the disease, scores of the Unified Parkinson's Disease Rating Scale and Hoehn and Yahr staging in PD patients. These values did not correlate with age in the control group. These results suggest that serum levels of zinc and copper do not play any role as risk factors for PD.

Serum levels of vitamin A in Parkinson's disease

To elucidate a possible role of vitamin A in the pathogenesis of Parkinson's disease (PD) we compared serum levels of retinol (vitamin A), measured by HPLC, and the vitamin A/retinol binding protein (RBP) ratio of 42 PD patients (22 males and 20 females, mean age 67.3 +/- 1.34 years) and their respective spouses as control group (20 males and 22 females, mean age 66.2 +/- 1.42). The serum levels of vitamin A did not differ significantly between the 2 groups (0.59 +/- 0.03 microgram/dl for PD patients and 0.57 +/- 0.03 microgram/dl for controls), nor did the vitamin A/RBP ratio (0.87 +/- 0.04 and 0.82 +/- 0.03, respectively). There was no influence of antiparkinsonian therapy on vitamin A or vitamin A/RBP ratio. Serum levels of vitamin A, and vitamin A/RBP ratio did not correlate with age, age at onset, scores of the Unified Parkinson's Disease Rating Scale or the Hoehn and Yahr staging in the PD group. These results suggest that serum concentrations of vitamin A, do not play a role in the pathogenesis of PD.