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

Ann Clin Biochem 2008;45:260-265
© 2008 Association for Clinical Biochemistry


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Original Articles

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}

Background: Targets for cholesterol reduction are part of the Quality OutcomesFramework and general practitioners have to meet these targetsto fulfil their remuneration package. By contrast, there areno targets for the accuracy of cholesterol or other lipid measurementsand no recent surveys on performance of these assays. We haveassessed the performance of lipid measurement of the availablemethods in the UK.

Methods: Serum samples collected from individual donors attending thenational blood service were distributed after values were obtainedfrom a secondary reference laboratory. Samples were sent toparticipant laboratories to assess different methods’ analyticalperformance on single donation specimens, on routine externalquality assessment pooled specimens, on specimens subjectedto a range of freeze–thaw cycles and on frozen-storedspecimens.

Results: Differences in measured cholesterol were found that were method-dependentand related to triglyceride content. HDL-cholesterol (HDL-C)showed significant positive bias in all assays. Individual donorspecimens showed no significant changes with differing numbersof freeze–thaw cycles. Pooled serum was stable for upto six months.

Conclusions: Most cholesterol measurements are accurate but some methodsare affected by triglyceride interference. HDL-C methods showsignificant positive bias. Although there are potential matrixeffects introduced as a result of specimen preparation, additionalwork is needed to show if these effects are present in freshpatient samples.

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