Annals of Clinical Biochemistry > Volume 45, Number 3 > Pp. 260-265

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Original Articles

Lipid external quality assessment: commutability between external quality assessment and clinical specimens

Robert Cramb¹, Jane French², Michael Mackness³, R Dermot G Neely⁴, Muriel Caslake⁵ and Finlay MacKenzie²

¹ Department of Clinical Biochemistry, University Hospital Birmingham NHS Foundation Trust, Birmingham B15 2TH, UK; ² UK NEQAS Wolfson EQA Laboratory, Institute of Research and Development, Birmingham Research Park, Birmingham, West Midlands B15 2SQ, UK; ³ Department of Medicine, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL; UK; ⁴ Department of Clinical Biochemistry, Newcastle Upon Tyne Hospitals, Newcastle Upon Tyne NE1 4LP, UK; ⁵ University Department of Vascular Biochemistry, 4th Floor, Queen Elizabeth Building, Glasgow Royal Infirmary, Alexandra Parade, Glasgow, G31 2ER, UK

Corresponding author: Dr Robert Cramb. Email: rob.cramb{at}uhb.nhs.uk

Background: Targets for cholesterol reduction are part of the Quality Outcomes Framework and general practitioners have to meet these targets to fulfil their remuneration package. By contrast, there are no targets for the accuracy of cholesterol or other lipid measurements and no recent surveys on performance of these assays. We have assessed the performance of lipid measurement of the available methods in the UK.

Methods: Serum samples collected from individual donors attending the national blood service were distributed after values were obtained from a secondary reference laboratory. Samples were sent to participant laboratories to assess different methods' analytical performance on single donation specimens, on routine external quality assessment pooled specimens, on specimens subjected to a range of freeze–thaw cycles and on frozen-stored specimens.

Results: Differences in measured cholesterol were found that were method-dependent and related to triglyceride content. HDL-cholesterol (HDL-C) showed significant positive bias in all assays. Individual donor specimens showed no significant changes with differing numbers of freeze–thaw cycles. Pooled serum was stable for up to six months.

Conclusions: Most cholesterol measurements are accurate but some methods are affected by triglyceride interference. HDL-C methods show significant positive bias. Although there are potential matrix effects introduced as a result of specimen preparation, additional work is needed to show if these effects are present in fresh patient samples.

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