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Triglycerides

Triglycerides are esters of glycerol and, usually, three different fatty acids. They are the main form of storage lipid in man and are transported in plasma, mostly in the form of chylomicrons and very low-density lipoprotein (VLDL). Plasma levels of triglycerides vary widely throughout the day because many grams of dietary fat are absorbed after each meal.

Historically, triglycerides have been overshadowed by cholesterol and HDL cholesterol as a risk factor for coronary artery disease (CAD). Multivariate analyses suggested that triglycerides were less important than HDL cholesterol. However, a 1996 meta-analysis involving 22,293 men and 6,345 women demonstrated that triglycerides are an independent risk factor for CAD even after adjustment for HDL cholesterol (J Cardiovasc Risk 1996; 3:321). The risk of CAD increased 37% in women and 14% in men for each 88.5 mg/dL increase in triglycerides.

The National Cholesterol Education Program Adult Treatment Panel II report, which was published in 1993, stated that a triglyceride level of less than 200 mg/dL is desirable, a level between 200 and 400 mg/dL is borderline high, and a level between 400 and 1000 mg/dL is high.

More recent studies have suggested that the NCEPs’ decision points are set too high. The Baltimore Coronary Observation Long-Term Study (COLTS) demonstrated that CAD patients with triglyceride levels between 100 and 199 mg/dL remained at increased risk, while patients with triglyceride levels below 100 mg/dL experienced a 50% reduction in secondary coronary events. In addition, the American Heart Association and the American College of Cardiology have endorsed a desirable triglyceride level of 150 mg/dL or less in women and diabetic patients (Circulation 1999; 99:2480). Based on this evidence, the triglyceride reference range was changed from <200 to <150 mg/dL on February 3.

A number of acquired disorders raise serum triglycerides, a change that may be particularly important in patients with underlying defects in triglyceride metabolism. These include:

• Obesity, often in association with hypercholesterolemia
• Diabetes mellitus, especially with poor glycemic control
• Nephrotic syndrome, often is association with hypercholesterolemia
• Hypothyroidism, often in association with hypercholesterolemia.
• Estrogen replacement, which is often associated with a fall in LDL-cholesterol
• Tamoxifen can cause marked hypertriglyceridemia in a minority of women
• Beta blockers
• Immunosuppressive medications such as glucocorticoids and cyclosporine. Glucocorticoid effect is associated with insulin resistance and may be mediated by ACTH suppression

Triglyceride levels above 1000 mg/dL place the patient at increased risk for acute pancreatitis, especially when combined with obesity, diabetes, and excessive alcohol consumption. See Lipid Profile.

Even in the fasting state, considerable biological variation occurs within individuals. Fasting triglyceride levels may vary as much as 25% in healthy individuals over a two-month period. Far greater fluctuations may be seen in sick patients. Treatment decisions should not be based on a single triglyceride level. Repeat samples should be drawn at least one week apart.

Reference range is <150 mg/dL.

Specimen requirement is one SST tube of blood collected after a 9 to 12 hour fast.