A recent change in the design format of patient request forms was instituted by the laboratory that I routinely use for chemical pathology analysis.
In a departure from the previous format the new forms include an option for fasting lipids, in which instance an analysis of lipoproteins HDL-C and LDL-C and Triglycerides is reported.
These lipoprotein fractions are not currently reported if the specimen is labelled “non fasting”, and only a total cholesterol level is reported in this instance. This renders a calculation of the total cholesterol/HDL-C ratio impossible, leaving the clinician without meaningful data regarding risk assessment.
I have never understood the rationale for subjecting patients to a fast preceding lipid analysis and have noted that the practice is quite widespread in the clinical setting.
Not infrequently healthy persons are found to have an elevated total cholesterol level, and then prescribed a statin, or advised to go on a “low cholesterol diet”, with instructions to return for a repeat fasting cholesterol analysis.
Both of these responses to an elevated total cholesterol are inappropriate, since an elevated total cholesterol level is, of itself, not a cause for concern in a healthy person, nor is it a reason for pharmaceutical intervention. Furthermore, a dietary restriction of cholesterol (the so called “low cholesterol diet”) has minimal impact on blood cholesterol levels and has no sound scientific basis or practical value.
An added danger of the fasting protocol is the possibility that dehydration associated with a fast may actually yield an abnormally higher lipid level which bears no relation to the normal daily level of the subject.
I have tried, without success, to determine whether the new laboratory protocol represents a directive from an authority that intends to standardise methods for lipid analysis by imposing a pre-sampling fast for patients.
Numerous studies, over many years, clearly demonstrate that dietary cholesterol has a minimal, and insignificant, effect on serum cholesterol, which in turn does not correlate with coronary heart disease or mortality across or within populations.
Either apo-lipoprotein A / B ratios, or total cholesterol/HDL-C ratios should be evaluated for purposes of risk assessment, and fasting has no significant clinical influence on either of these ratios.
Conversely, dietary saturated fats do affect total cholesterol levels, since they improve anti-atherogenic HDL-C levels and thereby reflect a higher total cholesterol level which should not be targeted for treatment !
Added to the unnecessary burden of patient anxiety, having been told that they have a raised total cholesterol level, is the inconvenience of fasting for a repeat test, with likelihood of further anxiety.
Compounding the problem is the possibility that an unwarranted pharmacological intervention will be imposed on the patient, creating not only unnecessary risks for an adverse event, but a serious burden for an already over-stretched health budget .
Data from the recently reported Emerging Risk Factors Collaboration support the contention that fasting is not necessary for lipid assessment and quantifying cardiovascular risk. (JAMA vol. 302 No. 18, Nov 11, 2009.)
Dr. Neville Wilson.
The Leinster Clinic – Medical Suite.
Dr Neville Wilson is a Doctor in Maynooth