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Published on: October 12, 2017
Lipid external quality assessment: commutability between external quality assessment and clinical specimens
Robert Cramb1, Jane French, Michael Mackness
1Department of Clinical Biochemistry, University Hospital Birmingham NHS Foundation Trust, Birmingham, UK. rob.cramb@uhb.nhs.uk
Insights
Accurate cholesterol measurement is crucial, but some methods show interference from triglycerides. High-density lipoprotein cholesterol (HDL-C) assays consistently exhibit positive bias, impacting lipid measurement accuracy.
Area of Science:
- Clinical Chemistry
- Laboratory Medicine
- Diagnostic Assays
Background:
- Quality Outcomes Framework mandates cholesterol reduction targets for general practitioners.
- No established targets exist for the accuracy of lipid measurements.
- Recent surveys on lipid assay performance are lacking.
Purpose of the Study:
- To assess the analytical performance of available lipid measurement methods in the UK.
- To identify method-dependent variations and interferences in cholesterol and HDL-C assays.
- To evaluate the stability of lipid measurements under various conditions.
Main Methods:
- Serum samples from individual donors and pooled specimens were used.
- Participant laboratories assessed analytical performance using different methods.
- Specimens were subjected to freeze-thaw cycles and assessed after frozen storage.
Main Results:
- Method-dependent differences in cholesterol measurements were observed, influenced by triglyceride content.
- High-density lipoprotein cholesterol (HDL-C) assays demonstrated significant positive bias across all methods.
- No significant changes in individual donor specimens were noted with varying freeze-thaw cycles; pooled serum remained stable for six months.
Conclusions:
- While most cholesterol measurements are accurate, triglyceride interference affects certain methods.
- Significant positive bias in HDL-C assays requires attention.
- Further research is needed to determine if matrix effects from specimen preparation impact fresh patient samples.
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.
