Fasting Versus Nonfasting Triglycerides: Implications for Laboratory Measurements (Perspectives‪)‬

Recent publications in the Journal of the American Medical Association (1, 2) report the superiority of the measurement of nonfasting over conventional fasting triglycerides in predicting risk for cardiovascular events, observations consistent with previous studies (3, 4). For decades the usual practice has been to measure triglycerides in blood samples obtained after patients have fasted 8-12 h, a procedure consistent with population studies that specified fasting blood collections to decrease variability and achieve consistency of metabolic state in patients at the time of sample collection (5). Triglyceride values fluctuate widely over time, with a CV of biological variability averaging about 23% and ranging up to 40%, and this variability can confound estimation of the associated cardiovascular disease (CVD) risk (6). Fasting blood collection is thought to decrease this variability (7), a theory supported by the observed correlation between fasting and nonfasting values (8). Nevertheless, because postprandial nonfasting values are more representative of the usual metabolic state, the observed improved prediction of the associated CVD risk is not unexpected. A change in practice to nonfasting collections, however, might affect other applications of the triglyceride determination or other measurements made on the specimens. Triglycerides are measured in clinical practice not only to assess CVD risk, but also to detect the extreme increases that can contribute to pancreatitis. For this purpose the question of fasting vs nonfasting is largely irrelevant; in fact such high levels could be detected by visual observation of the extent of turbidity and/or a floating fat layer associated with the larger triglyceriderich lipoprotein (TRL) particles. Triglyceride-associated turbidity, likely increased in nonfasting specimens, can interfere with other laboratory determinations, necessitating thorough studies with various instrument/reagent systems.