The Journal of the American Medical Association has published the results of study that aimed to assess the association between levels of the major blood lipids and apolipoproteins with the risk of vascular disease. The results of the study have been reported in the wider media (BBC).
Data for 302,430 individuals from 68 studies with 2.79 million person-years of follow up were analysed. During the studies the following outcomes occurred: 8857 nonfatal myocardial infarctions, 3928 coronary heart disease (CHD) deaths, 2534 ischaemic strokes, 513 haemorrhagic strokes, and 2536 unclassified strokes.
This analysis found strong correlations between cardiovascular risk and levels of high-density lipoprotein cholesterol (HDL-C), non-high-density lipoprotein cholesterol and triglycerides after correcting for other non-lipid risk factors. After additional correction for the other lipid variables the association with triglycerides was no longer statistically significant. The association remained significant after this same correction for HDL-C and non-HDL-C. Levels of apolipoproteins were not associated more strongly than HDL-C or non-HDL-C.
The authors conclude that, "lipid assessment in vascular disease can be simplified by measurement of either total and HDL cholesterol levels or apolipoproteins without the need to fast and without regard to triglyceride".
There are several potential merits to these conclusions. The possibility of simplifying cholesterol testing so that fasting is not required is likely to be highly acceptable to patients. It would also seem that apolipoprotein levels provide no additional clinical insight to guide treatment choices. However, clinicians may need to bear in mind than many laboratories calculate LDL-C using the Friedewald equation rather than directly assessing the level of LDL-C. The accuracy of this equation declines at elevated triglyceride levels and fasting samples will still be required for accurate reporting of LDL-C.
Action: Any changes to blood test requesting need careful planning. Total cholesterol and HDL-C can be assessed from a non-fasting blood sample for the purposes of cardiovascular risk prediction however fasting samples will still be necessary in many cases.