GPs do not need to ask patients to fast before taking a cholesterol test as it makes very little difference to the results, a large-scale study has suggested.
Canadian researchers found that mean levels of total cholesterol and HDL-cholesterol varied by less than 2% among individuals with fasting times of between one and 16 hours.
The researchers concluded fasting for routine lipid levels was ‘largely unnecessary’, contradicting best practice as recommended by NICE and the Joint British Societies.
Their study looked at the laboratory results of blood samples from 111,048 women and 98,132 men in the community and cross-referenced this with the duration they had fasted before the sample was taken.
The data was from a six-month period in 2011 and researchers controlled for the differing age of patients. They then estimated the mean levels of cholesterol subclasses recorded at different fasting times.
The mean levels of total cholesterol and HDL-cholesterol differed little among individuals with various fasting times, with variations of less than 2%.
Fasting times of up to five hours did show statistically significant differences among the calculated LDL-cholesterol levels and triglycerides compared with either a nine to 12-hour fasting time or a greater than eight-hour fasting time.
But the variations in the calculated LDL-cholesterol levels were low, with a variation of less than 10% among groups of patients with different fasting intervals. Mean triglyceride levels showed variations of up to 20%.
NICE guidelines currently recommend everyone should have ‘at least one’ fasting blood test to measure total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides’. The JBS2 guidelines also recommend a fasting sample ‘to measure a full lipoprotein profile’ in patients at high cardiovascular risk.
But the researchers said their results confirmed the findings of a number of smaller studies that fasting tests were not needed.
The authors concluded: ‘We found that fasting time showed little association with lipid subclass levels in a large community-based cohort.
‘This finding suggests that fasting for routine lipid level determinations is largely unnecessary.’
Dr Mike Knapton, associate medical director of the British Heart Foundation and a part-time GP in Cambridge, said the findings of the paper would reduce the ‘hassle’ of cholesterol testing for both patients and GPs.
He said: `This paper confirms that there’s little relationship between cholesterol and fasting levels.
At the moment all the cardiovascular algorithms are usually based on either total cholesterol or total cholesterol to HDL ratio. So I would continue to do cholesterol levels on nonfasting blood, and just select the smaller number of patients for whom I want fasting glucose or fasting lipids.’
