Triglycerides: what the test measures, normal and high levels, and what raises them

Triglycerides are molecules of three fatty acids attached to a glycerol backbone — the form in which dietary fat is absorbed, in which the liver packages fat it makes from excess carbohydrate and alcohol, and in which fat is stored in adipose tissue. In the blood they travel inside chylomicrons after a meal and inside VLDL particles made by the liver between meals. The test measures the total triglyceride concentration in serum, whichever particle is carrying it.

Because chylomicrons flood the blood for several hours after eating, triglycerides are the lipid most affected by a recent meal, which is why a fasting draw has traditionally been required and why a non-fasting value is read against a higher threshold (about 175 rather than 150). The measurement itself is an enzymatic assay and is well standardized.

Triglycerides matter in two ways. Moderately high levels mark insulin resistance and travel with the small, dense LDL and low HDL that raise heart risk; the triglyceride-rich particles themselves also carry cholesterol into plaque, which is why non-HDL cholesterol and ApoB are used to capture them. Very high levels — above 500, and especially above 1,000 — can inflame the pancreas directly.

Triglycerides are on every lipid panel and are checked with cholesterol: a first panel in young adulthood, every four to six years at low risk, and more often with diabetes or prediabetes, obesity, high blood pressure, kidney disease, fatty liver or a family history of early heart disease or very high triglycerides. A high triglyceride level is one of the five criteria of metabolic syndrome.

People with a history of pancreatitis, those on medications that raise triglycerides (estrogen, retinoids, some antipsychotics and HIV drugs, corticosteroids, thiazides and older beta-blockers) and heavy drinkers are tested more deliberately. Anyone starting a fibrate, omega-3 prescription or statin for a high level is retested after six to twelve weeks.

Triglycerides come on the standard lipid panel with total cholesterol, LDL and HDL, which a doctor can order or you can order online through TestWell for a draw at a Quest or Labcorp patient service center; a licensed physician reviews the order and results post to your portal within one to three business days against the fasting bands. Metabolic and wellness panels that include a lipid panel carry them too.

Fast for nine to twelve hours before the draw — water is fine, and usual medications can be taken — because a meal within the previous few hours can double the value. Avoid alcohol for at least 24 hours and ideally two to three days, since alcohol raises triglycerides more than any other common exposure, and avoid an unusually heavy or sugary dinner the night before. Intense exercise the day before lowers them modestly.

A single high result is repeated before it is acted on, because triglycerides vary by 20 to 30 percent from day to day in the same person. Mention recent weight change, pregnancy, thyroid problems, diabetes control and the medications above to the ordering physician.

For a fasting sample the categories are: normal under 150 milligrams per deciliter; borderline high 150 to 199; high 200 to 499; very high 500 and above. Current guidelines treat 175 or more on a non-fasting sample, or 150 or more fasting, as a risk-enhancing factor in deciding on statin therapy, and most laboratories print the full scale. Divide by about 88.6 to convert to millimoles per liter.

The bands are the same for men and women and across adult ages, although levels rise with age and weight and are higher in men until women reach menopause. In children, normal is under 75 for ages 0 to 9 and under 90 for ages 10 to 19. Pregnancy raises triglycerides two- to three-fold by the third trimester, which is normal and resolves after delivery.

Above 500, and particularly above 1,000, the concern shifts from heart disease to acute pancreatitis, and treatment aims first at bringing the level down; genetic causes (familial chylomicronemia and related disorders) are considered when levels this high appear early or run in families.

Lifestyle drives most elevations: excess calories in general and refined carbohydrate and sugar in particular (the liver converts the surplus to triglyceride), alcohol, excess weight, and inactivity. Insulin resistance, prediabetes and type 2 diabetes raise triglycerides because insulin normally restrains the liver's output of VLDL and clears fat from the blood; poorly controlled diabetes can push levels into the thousands.

Secondary causes to exclude include an underactive thyroid, chronic kidney disease and nephrotic syndrome, fatty liver, pregnancy, and medications — estrogen pills (less so patches), tamoxifen, retinoids, corticosteroids, thiazides and older beta-blockers, some antipsychotics, antiretroviral drugs and immunosuppressants. Genetic disorders of triglyceride metabolism are uncommon but produce very high levels and often a family history of pancreatitis.

Moderately high triglycerides cause no symptoms. Very high levels can cause abdominal pain from pancreatitis, small yellow bumps on the skin (eruptive xanthomas), a milky appearance of the blood sample, and in extreme cases memory problems or breathlessness. The response to a high level is first to repeat it fasting, then to address diet, alcohol, weight and glucose, which lower triglycerides more reliably than they lower any other lipid.

Low triglycerides are almost always good news: a lean, active person on a diet low in refined carbohydrate typically runs 40 to 80 milligrams per deciliter, and there is no healthy lower limit. Levels under about 40 occasionally accompany an overactive thyroid, malabsorption or malnutrition, advanced liver disease, or rare inherited disorders of lipoprotein production, and very low values in someone who is unwell are worth noting to a clinician.

A low triglyceride with a low HDL and high LDL is a different and more concerning pattern than a low triglyceride with a high HDL; the panel is read as a whole.

A high triglyceride level is a prompt to look at glucose handling: a fasting glucose or A1c, and sometimes a fasting insulin, because insulin resistance is the commonest explanation. The triglyceride-to-HDL ratio (above about 3 in milligram units) is a quick marker of the same pattern. Liver enzymes (ALT, AST, GGT) screen for the fatty liver that accompanies high triglycerides, and a TSH excludes an underactive thyroid.

Because the Friedewald LDL calculation fails above 400, laboratories switch to a direct LDL or a newer equation at high triglyceride levels, and non-HDL cholesterol or ApoB becomes the more reliable guide to plaque-forming particles. For very high levels, a repeat fasting panel after a period of alcohol abstinence and dietary change shows how much is lifestyle and how much is genetic.