As a cardiac risk factor triglycerides have occupied an uneasy position for a long time: perpetually under a cloud of suspicion but never proved to cause or even have a definite association with the risk of coronary heart disease. There are good grounds for suspicion — biological plausibility and epidemiological data suggest that triglycerides might promote coronary heart disease and other forms of cardiovascular disease — but the epidemiological and clinical evidence is inconsistent and often flawed. Even recent recommendation calling for the use of triglyceride concentration in screening are qualified by two admissions: that the evidence for a causal link remains frail and that trials have not established any clinical benefit from measuring triglyceride concentration.*RF 1–3*

Why should a final judgment about the importance of triglycerides in cardiovascular disease remain so elusive? One cause is the variability of measurements of triglyceride concentrations — much greater than for other common lipids. This is partly due to the laboratory and partly to “true” short term fluctuations. This variability helps explain why statistical techniques underestimate the association between triglyceride concentration and the risk of coronary heart disease.^4,5 Clinicians can reduce the influence of physiological variability in triglyceride values by averaging repeated measurements — just as they …