Removing Lipemia in Serum/Plasma Samples: A Multicenter Study.

BACKGROUND: Lipemia, a significant source of analytical errors in clinical laboratory settings, should be removed prior to measuring biochemical parameters. We investigated whether lipemia in serum/plasma samples can be removed using a method that is easier and more practicable than ultracentrifugation, the current reference method. METHODS: Seven hospital laboratories in Spain participated in this study. We first compared the effectiveness of ultracentrifugation (108,200×g) and high-speed centrifugation (10,000×g for 15 minutes) in removing lipemia. Second, we compared high-speed centrifugation with two liquid-liquid extraction methods-LipoClear (StatSpin, Norwood, USA), and 1,1,2-trichlorotrifluoroethane (Merck, Darmstadt, Germany). We assessed 14 biochemical parameters: serum/plasma concentrations of sodium ion, potassium ion, chloride ion, glucose, total protein, albumin, creatinine, urea, alkaline phosphatase, gamma-glutamyl transferase, alanine aminotransferase, aspartate-aminotransferase, calcium, and bilirubin. We analyzed whether the differences between lipemia removal methods exceeded the limit for clinically significant interference (LCSI). RESULTS: When ultracentrifugation and high-speed centrifugation were compared, no parameter had a difference that exceeded the LCSI. When high-speed centrifugation was compared with the two liquid-liquid extraction methods, we found differences exceeding the LCSI in protein, calcium, and aspartate aminotransferase in the comparison with 1,1,2-trichlorotrifluoroethane, and in protein, albumin, and calcium in the comparison with LipoClear. Differences in other parameters did not exceed the LCSI. CONCLUSIONS: High-speed centrifugation (10,000×g for 15 minutes) can be used instead of ultracentrifugation to remove lipemia in serum/plasma samples. LipoClear and 1,1,2-trichlorotrifluoroethane are unsuitable as they interfere with the measurement of certain parameters.

¿Podemos utilizar la apolipoproteína B en la toma de decisiones para la intervención en el riesgo cardiovascular de pacientes con triglicéridos elevados? / Can apolipoprotein B be used for making decisions on cardiovascular risk prevention in patients with raised triglycerides?

Objetivo. Analizar el valor predictivo de diversas aproximaciones: cuantificación de la concentración de apolipoproteína B (apoB), estimación del cLDLf y estimación del no-cHDL, como predictivos de elevaciones de la magnitud de la concentración de cLDL. Material y métodos. Estudio multicéntrico transversal en el que se han analizado las muestras rutinarias de 6.094 pacientes consecutivos. En cada paciente se ha cuantificado el cLDL mediante una técnica de ultracentrifugación de rutina (cLDLu) y la concentración de apoB por uno de los métodos inmunológicos estandarizados y se ha estimado el cLDLf y el no-cHDL. Las magnitudes obtenidas han sido utilizadas para analizar sus valores predictivos del cLDLu en función de tres grupos de concentración de Tg (<200, entre 200 y 400 y más de 400mg/dL) y los grupos de riesgo definidos por el ATPIII (cLDL>70, 100, 130 o 160mg/dL). Resultados y conclusiones. Con todas las magnitudes analizadas se obtiene un buen valor predictivo positivo, variable para las diferentes concentraciones de Tg y que es máximo para la apoB con puntos de corte de alta especificidad (AE). Las estimaciones con cLDLf infraestiman la situación de riesgo del paciente, mientras que las que utilizan el no-cHDL la sobreestiman. Conclusión. En pacientes con Tg<200mg/dL puede utilizarse prácticamente sin riesgo la fórmula de Friedewald; en pacientes con Tg elevados es recomendable la apoB (puntos de corte de AE) como predictor positivo y el no-cHDL como predictor negativo (AU)

Objective. To analyse the predictive value of several approaches to cardiovascular risk prevention: measuring apolipoprotein B concentrations (apoB), estimation of fractionated LDL cholesterol (cLDLf) and non-HDL cholesterol (HDLc), to predict increases in LDL cholesterol. Material and Methods. Cross-sectional multicentre study in which routine samples from 6094 consecutive patients were analysed. In each patient, LDLc was quantified by routine ultracentrifugation technique (LDLu) and apoB concentrations by a standard immunological method. We also estimated the LDLf and non-HDLc. The values obtained were used to analyse the predictive values of unfractionated LDL cholesterol (cLDLu) into three groups according to their triglyceride concentration (<200, between 200 and 400 and 400mg/dL) and risk groups as defined by the Adult Treatment Panel (ATP) III guidelines (LDL-C> 70, 100, 130 or 160mg/dL). Results and conclusions. With all the variables analysed we obtained a good positive predictive value, which varied according to the triglyceride concentrations, with the highest values being obtained for apoB with high specificity cut-off points (AE). Calculations with LDLf values underestimate the patient's risk, while those using non-HDLc overestimate it. Conclusion. The Friedewald formula can be used practically without risk in patients with triglycerides below 200mg/dL. In patients with elevated triglycerides, apoB (AE cut-off points) is recommended as a positive predictor, and non-HDLc as a negative predictor (AU)

Evaluación multicéntrica de distintos métodos para la determinación de colesterol HDL directo con respecto al colesterol HDL de precipitación / Multicentre evaluation of different methods for the determination of direct HDL-cholesterol compared to the precipitation method

Introducción. Los resultados de los programas de garantía de calidad indican que existen diferencias significativas entre los métodos homogéneos disponibles para la medición del colesterol HDL. Sin embargo, la posible influencia de efectos matriz en las muestras liofilizadas empleadas y la ausencia de un valor verdadero en estas muestras, hace difícil la valoración completa de estos métodos. En este estudio experimental multicéntrico hemos comparado los métodos homogéneos más utilizados en nuestro medio, con respecto al de precipitación de ácido fosfotúngstico-MgCl2. Material y métodos. Cada laboratorio procesó unas 100 muestras de suero de pacientes por uno o dos métodos homogéneos y envió alícuotas congeladas de las muestras analizadas al laboratorio central donde se procesaron por el método de precipitación. Resultados. Las imprecisiones de los métodos homogéneos fueron buenas e inferiores a las de precipitación, que cumplía las especificaciones de calidad para sesgo y error total (ET). Sin embargo, no todos los métodos homogéneos cumplían los objetivos de calidad mínimos, pues algunos procedimientos producían sesgos positivos muy altos (en relación al método de comparación) y uno un sesgo negativo muy bajo. El estudio de la concordancia, realizado estratificando a los pacientes según las concentraciones de colesterol HDL, mostró diferencias entre los métodos. Conclusiones. Estos resultados sugieren que existen discrepancias en la valoración de las magnitudes obtenidas con los métodos homogéneos, probablemente generada por una elevada inexactitud en algunos de ellos y que es conveniente que los laboratorios conozcan las caracteristicas de imprecisión y sesgo del metodo directo que utilizan con respecto al de referencia (AU)

Introduction. The results of quality assurance programs suggest that there are significant differences between the homogeneous methods available for the measurement of HDL cholesterol. However, the possible influence of matrix effects in the lyophilized samples used and the absence of a true value in these samples means that a full assessment of these methods cannot be made. In this multicentre pilot study we compared the most used homogeneous methods in our country with the phosphotungstic acid-MgCl2 method. Material and methods. Each laboratory processed about one hundred serum samples from patients with one or two homogeneous methods and sent frozen aliquots of the samples in special packaging with dry ice to the central laboratory where they were processed by the precipitation method. Results. The imprecision of homogeneous methods were good and lower than those of the precipitation method, and met the quality specifications for bias and total error (TE). However, not all homogeneous methods met the minimum quality objectives, as some procedures produced a very high positive bias (relative to the comparison method) and one, a low negative bias. In addition, the study of the agreement between methods, made by stratifying patients according to HDL cholesterol concentrations, showed differences. Conclusions. These results suggest that there are discrepancies in the assessment of the levels obtained with homogeneous methods, probably due to a high inaccuracy in some of them, and it is advised that the laboratories be aware of the characteristics of inaccuracy and bias of the direct method used compared to the reference method (AU)

Multicentric evaluation of the homogeneous LDL-cholesterol Plus assay: comparison with beta-quantification and Friedewald formula.

OBJECTIVES: To evaluate the analytical and clinical performance of a new version of the LDL-C Plus assay and compare it with the beta-quantification (BQ) method in a multicenter study. DESIGN AND METHODS: Direct LDL-C was measured in 169 fresh pooled samples and in 830 clinical samples with known LDL-C by BQ. The reactivity of lipoproteins and the effect of hemoglobin, bilirubin and chylomicrons (CM) were studied. RESULTS: Direct LDL-C total imprecision was <2.2%; inaccuracy <+/-2.5% (unaffected by triglycerides up to 9.5 mmol/L); and total error 9.8%. Direct assay reacted with 95%, 50% and 25% of the cholesterol in the LDL, intermediate (IDL) and VLDL fractions, respectively. A significant association was observed with BQ. Icteric samples showed a negative bias and the effect of CM was variable. A positive bias was observed when VLDL-cholesterol/triglyceride ratio was >0.57. CONCLUSIONS: LDL-C Plus assay represents a valid alternative to BQ for clinical laboratories.