Asking patients to come in fasting state for a blood test is a major inconvenience. Fortunately, most blood tests, even glycemic management, can be done in non-fasting state, as increasing reliance is placed on HbA1C.
The practice, however, is very rigid on lipid measurements – doctors insist on getting fasting lipid profile. Laboratories refuse to test if patients are not fasting and ask them to come back in the fasting state.
There is increasing evidence that we do not need to get lipids done after an overnight fast in most situations. Non-fasting levels are as good – which makes sense as most of the day we are in a non-fasting state.
The historic reasons for getting lipid levels done in a fasting state are related to methodological issues going back to 1967. The classification of hypertriglyceridaemia was made at that time based on fasting levels, and LDL cholesterol was calculated using the Friedwald formula on fasting data.
The initial lipid guidelines strongly focused on bringing down the lipid levels and made recommendations based on specific blood levels, which were used as indication to start therapy and as targets.
An important change in recent years is that the focus has now moved to estimating 10 year coronary disease risk using multiple parameters rather than using cholesterol level alone.
Further, data has emerged in recent years, most notably from Scandinavian countries, that there is not much difference between fasting and non-fasting lipid values. As a result, increasing number of professional societies and organisations now recommend using non-fasting lipid levels to establish the cardiovascular risk status.
Situations where fasting levels are needed are: when non-fasting triglyceride levels are above a certain threshold, for calculating the residual risk in treated patients, or to estimate the risk of starting induced diabetes. Those presenting with secondary causes should also undergo fasting testing.
To assess the initial risk of atherosclerotic cardiovascular disease in an untreated patient, you only need fasting or non-fasting total cholesterol and HDL-cholesterol.
Key recommendations from the European atherosclerosis Society and European Federation of Clinical and Laboratory Medicine
- Fasting is not required routinely for assessing the plasma lipid profile
- When non-fasting plasma triglyceride concentration > 440 mg/dL, repeat the lipid profile in the fasting state
- Laboratory reports should flag abnormal values based on desirable concentration cut-points
- Life-threatening or extremely high concentrations should trigger an immediate referral to a lipid clinic or to a physician with special interest in lipids
Consumption of high-fat meal before testing can increase triglyceride and lowers LDL-cholesterol levels, so patients should be asked to avoid such food items on the day of test.
Many population-based studies and statin trials have employed non-fasting lipid levels to assess cardiovascular risk and study outcomes.
When to use non-fasting and fasting blood sampling to assess lipid profile – European Atherosclerosis Society (Nordestgaard et al, Eur Hear J. April 26, 2016)
When to use non-fasting and fasting blood sampling to assess lipid profile – American Heart Association/American College of Cardiology (Driver et al. JACC 2016 67: 1227–34)
Population-based studies totalling >300 000 non-fasting individuals
- Tromsø Heart Study
- Norwegian National Health Service
- British Population Studies
- European Prospective Investigation of Cancer–Norfolk
- Northwick Park Heart Study
- Apolipoprotein-related Mortality Risk
- Copenhagen City Heart Study
- Women’s Health Study
- Nurses’ Health Study
- Physicians’ Health Study
- NHANES III
- Circulatory Risk in Communities Study
- Copenhagen General Population Study
- The global 52-country case-control
- INTER HEART study
Statin trials totalling 43 000 non-fasting individuals
- Heart Protection Study
- Study of the Effectiveness of Additional Reductions in Cholesterol and Homocysteine
- Anglo-Scandinavian Cardiac Outcomes Trial—Lipid Lowering Arm