Investigating the effects of endogenous lipaemia on the measurement of sodium by indirect ion specific electrode potentiometry.

BACKGROUND: The widely automated method using indirect ion specific electrodes (ISE) potentiometry for determination of sodium concentration is prone to interference from lipaemia. Manufacturer-specified lipaemic (L)-index cut offs may underestimate the effects of endogenous lipaemia. METHODS: We assessed the interference on sodium concentration caused by endogenous lipaemia in 32 residual samples (from 13 patients) using indirect ISE (Cobas® 8000 modular analyser with c702 module, Roche diagnostics) and direct ISE (GEM 4000 premier, Werfen) potentiometric methods. Regression analysis (linear and non-linear) was used to determine a reliable (L)-index cut off for reporting sodium concentration. RESULTS: There was a poor correlation observed between triglyceride concentration and (L)-index. There was significant negative interference caused by endogenous lipaemia within analysed samples. Non-linear regression demonstrated a negative interference of approximately 5% at an (L)-index of 250. CONCLUSION: At present, the manufacturer advises not to report sodium concentration by indirect ISE on the Cobas® 8000 modular analyser if the (L)-index is >2000. However, this has been determined by the addition of exogenous lipids (Intralipid®) and it is clear that this is not comparable to endogenous lipaemia. To ensure patient safety, clinical laboratories should consider lowering the cut off for (L)-index that they use for reporting sodium concentration.

Stabilization of Plasma Glucose: The Use of Newer Technology and Pragmatic Laboratory Practice.

BACKGROUND: The target values for plasma glucose concentrations for the investigation and diagnosis of diabetes and impaired fasting glucose, and the realization that small incremental changes in glucose concentration increase the risk of adverse events, has led to greater focus on laboratory glucose results. Although analytical methods show acceptable precision, the control of preanalytical error due to the stability of glucose remains problematic. The aim of this study was to compare glucose concentrations in 3 different and commercially available blood tubes, with analysis and storage under current practices and conditions. METHODS: Blood samples for glucose were obtained from consenting patients attending the Diabetic Clinic at the Royal Victoria Hospital, Belfast. Blood was collected into BD Vacutainer® Barricor™ Lithium Heparin tubes, BD Vacutainer Fluoride EDTA tubes, and Greiner Vacuette® FC-Mix (sodium fluoride/citrate/Na2EDTA) tubes in that order. The Barricor tubes were immediately centrifuged at 4000g for 3 min. All samples were then sent to the Biochemistry Laboratory for analysis on the same day, and again the following day after storage at 4 °C. RESULTS: There was no significant difference in mean glucose concentrations between immediately centrifuged Barricor and FC-Mix tubes when analyzed on day 0. Both tube types demonstrated higher mean glucose concentrations than traditional fluoride EDTA (F/EDTA) samples. CONCLUSIONS: Both immediately separated Barricor and citrated FC-Mix plasma preserve glucose concentrations to the same extent, and better than F/EDTA preservative. These newer technologies involved offer pragmatic solutions to improved glucose analysis, allowing laboratories to choose the best option given the source of their samples.

A national survey of troponin testing and recommendations for improved practice.

BACKGROUND: The introduction of troponin assays with higher analytical sensitivity and enhanced performance has produced new challenges for both laboratory and clinician in the optimal investigation of patients with cardiovascular disease. After some years of collective experience with this new generation of assays, this survey aimed to assess the level of consensus that exists regarding their application. METHODS: A questionnaire was designed, based on a review of published evidence and current opinion, to obtain information on a number of key areas relating to troponin analysis and reporting and was circulated to lead laboratory consultants across the UK and Ireland. RESULTS: Completed questionnaires were received from 94 laboratory contacts. Sixty per cent of those who responded had implemented a high-sensitivity troponin assay, with the Roche Cobas troponin T high sensitivity assay the most widely used. It is evident that some confusion remains regarding the definition of high-sensitivity assays and there was considerable variation in practice, even among those using the same manufacturer's assay. CONCLUSIONS: There is a need for greater consensus in the approach to the clinical utilization of troponin assays with improved sensitivity and it is important that laboratories are fully aware of the capabilities of their assay and provide useful guidance to users. On the basis of survey findings and the existing evidence base, a number of recommendations have been proposed to improve current practice and enhance patient safety.

Retinal vein occlusion, homocysteine, and methylene tetrahydrofolate reductase genotype.

PURPOSE: The aim of this case-control study was to investigate the relationship between homocysteine (tHcy), 5,10 methylene tetrahydrofolate reductase (MTHFR) C677T genotype, folate and vitamin B12 status, and retinal vein occlusion (RVO). METHODS: Subjects with RVO (n = 106) were recruited from outpatient and inpatient sources. Controls (n = 98) were selected to achieve a similar age and sex distribution. Full ocular examination was performed and medical history was taken for each study participant. Plasma and serum samples were analyzed for tHcy level and folate and vitamin B12 status, and extracted DNA was assessed for the MTHFR C677T genotype. RESULTS: There was no significant difference in plasma tHcy level or thermolabile MTHFR allele frequency between subjects and controls. Similarly, there was no significant difference in folate or vitamin B12 status between subjects and controls. MTHFR genotype did not affect folate or vitamin B12 concentrations in subjects or controls. However, tHcy was significantly higher in thermolabile homozygotes than in nonthermolabile homozygotes (ratio of geometric means, 1.35; 95% confidence interval [CI], 1.04-1.74; P = 0.024). CONCLUSIONS: Hyperhomocysteinemia, the MTHFR C677T mutation, and folate and vitamin B12 status are not important risk factors for RVO in this population.

Soluble vascular endothelial growth factor receptor-1 (sFlt-1) is increased throughout gestation in patients who have preeclampsia develop.

OBJECTIVE: This study was undertaken to analyze prospectively circulating vascular endothelial growth factor (VEGF) and its soluble receptor, (s) Flt-1, throughout normotensive and preeclamptic pregnancies and to assess the importance of these proteins in the development of preeclampsia. STUDY DESIGN: In this longitudinal cohort study, serum samples were collected from recruited subjects throughout pregnancy at 12, 20, 30, and 37 weeks and in the 24 hours before and after delivery. Subjects were divided retrospectively into normotensive and preeclamptic groups. Circulating VEGF and sFlt-1 concentrations were analyzed by radioimmunoassay and enzyme-linked immunosorbent assay, respectively. RESULTS: Circulating sFlt-1 and VEGF significantly increased as gestation progressed and both were further elevated in preeclampsia compared with normotensive pregnancy. Soluble Flt-1 concentrations were elevated early in gestation and were significantly increased at 30 weeks' gestation in those who subsequently developed preeclampsia. CONCLUSION: These results indicate a definite association between elevated sFlt-1 concentrations and the onset of preeclampsia suggesting that sFlt-1 is linked with disease pathogenesis.