Fasting is unnecessary for routine cholesterol and triglyceride tests

Cholesterol and triglycerides, 'lipids', have traditionally been measured in a fasting state. A valuable study just published in the Archives of Internal Medicine offers welcome evidence that fasting before lipid profiles is unnecessary in most cases and may even be superior. The authors state:

"Although current guidelines recommend measuring lipid levels in a fasting state, recent studies suggest that nonfasting lipid profiles change minimally in response to food intake and may be superior to fasting levels in predicting adverse cardiovascular outcomes... The purpose of this study was to investigate the association of fasting duration (in hours) with lipid levels in a large community-based population. We hypothesized that lipid levels would not vary significantly with duration of fasting time."

The authors note that earlier studies have questioned the need for fasting: and suggest that the non-fasting state may be a better clinical predictor:

"Fasting recommendations were originally introduced to decrease variability and achieve consistency in the metabolic states of patients at the time of sample collection. Several studies, however, suggest that the measurement of lipid subclasses in a nonfasting state is an acceptable alternative, with some nonfasting markers being better at predicting the risk of cardiac events. Studies suggest that lipid levels vary relatively little between the fasting and the nonfasting states and that the risk of coronary heart disease and strokes is similarly increased for both nonfasting and fasting lipid levels. Furthermore, as humans are usually in a nonfasting state, nonfasting values may be more representative of usual metabolic conditions. Measurement of nonfasting lipid profiles may also be better able to reveal individual metabolic abnormalities in lipid clearance, which may ultimately better predict cardiovascular disease risk."

They examined laboratory data that included the duration of fasting duration, cholesterol and lipid results over a 6-month period in 2011 for 209,180 individuals (111,048 females and 98,132 males). Their main outcome measures were the levels of high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, total cholesterol, and triglycerides for fasting intervals from 1 hour to more than 16 hours. This data was analyzed to estimate the mean levels of cholesterol subclasses at different fasting times. Their data showed that fasting had very little effect on the main risk factor predictors:

"The mean levels of total cholesterol and high-density lipoprotein cholesterol differed little among individuals with various fasting times. The mean calculated low-density lipoprotein cholesterol levels showed slightly greater variations of up to 10% among groups of patients with different fasting intervals, and the mean triglyceride levels showed variations of up to 20%."

The authors' comments are of great interest to all clinicians managing cardiovascular and metabolic risk factors:

"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. Our study corroborates the findings of previous smaller studies."

Fasting prior to phlebotomy is inconvenient, uncomfortable and an impediment to compliance. Moreover...

"Previous work has shown that peak triglyceride levels measured 4 hours after meals yielded the strongest predictive relationship of cardiovascular events."

As for the crucial matter of insulin regulation:

"Also, it has been reported that insulin resistance is associated with worse postprandial lipid or lipoprotein clearance and that increased postprandial triglyceride levels and decreased HDL cholesterol levels are excellent predictors of insulin resistance, a key metabolic abnormality in type 2 diabetes. These findings suggest that analysis of fasting time and lipid levels could have a role in identifying individuals for further screening with supplementary tests such as oral triglyceride tolerance testing or more rigorous treatment protocol goals and closer monitoring."

For many patients fasting before phlebotomy perturbs their system and introduces artifact into the data due to the stress involved. The authors conclude:

"Fasting times showed little association with lipid subclass levels in a community-based population, which suggests that fasting for routine lipid levels is largely unnecessary."

The author of an accompanying editorial also states:

"The incremental gain in information of a fasting profile is exceedingly small for total and HDL cholesterol values and likely does not offset the logistic impositions placed on our patients, the laboratories, and our ability to provide timely counseling to our patients. This, in my opinion, tips the balance toward relying on nonfasting lipid profiles as the preferred practice...Therefore, in practice, you can begin with a nonfasting lipid profile, and it is possible to use nonfasting levels for risk assessment, decisions about initiating treatment, and monitoring the effects of treatment. If you want to monitor triglyceride levels, then doing some sample fasting may useful. With this approach, most of our lipid profiles can be obtained in the nonfasting state, increasing convenience for our patients and ourselves and decreasing the burden on the laboratory, with no real adverse effect on clinical decision making."

Up until now I have allowed non-fasting blood draws for patients whose hypoglycemic predilection complicated phlebotomy and skewed data due to the stress effects. Now a fasting blood draw is going to be the exception rather than the rule in my practice.