Q: I recently had some blood tests at a health fair. Among the abnormal results were low cholesterol (25, with the normal range listed as 120 to 289) but high triglycerides (307, with a normal range of 30 to 175). There wasn't any more information than that. I've heard a lot about the health risks of high cholesterol, but is a cholesterol that's very low good or not? And isn't this range of normal much higher than what I've seen in the newspaper lately? Also, is my level of triglycerides dangerously high?

A: Your question brings up several issues about screening tests done at health fairs, something I'm generally not in favor of.

Your cholesterol level is actually extremely low -- so low it makes me wonder whether the test is in error. In rare cases, some people inherit a disorder of blood fats (lipoproteins) that makes their cholesterol level very low. Other causes of low cholesterol levels are malnutrition, liver disease and an overactive thyroid gland (hyperthyroidism), but these conditions wouldn't lower your cholesterol level that drastically.

Surprisingly, very low levels of cholesterol are actually linked with an increased risk of cancer. Although researchers initially thought this connection was the result of an already established, though undiagnosed cancer, very low cholesterol levels now seem to point to an increased tendency to develop cancer in the future.

By the way, I also question the "normal" range of 120 to 289 you were given. Recent National Institutes of Health guidelines give much lower values for a desirable level -- under 200 milligrams per deciliter of blood for people with other risk factors for heart disease, and under 240 for people with no other risk factors. Although many medical laboratories give the normal range for cholesterol as high as your figures, most doctors would probably advise aiming for levels more in keeping with the new NIH recommendations.

As for your triglycerides, they, like cholesterol, are fats made in the liver, which then circulate in your bloodstream; unlike cholesterol, these substances don't signal the same risk of hardening of the arteries (atherosclerosis) and heart disease.

In rare instances, very high levels of triglycerides (in the thousands) may lead to painful inflammation of the pancreas (pancreatitis). In some cases, high triglycerides point to some other disorder, such as diabetes, excessive alcohol use, liver disease or an underactive thyroid gland (hypothyroidism). As with high cholesterol levels, high triglyceride levels run in some families.

The trouble with getting multiple tests done at health fairs is that you're left with a bewildering array of data that may not make any sense. You may draw wrong conclusions about the information at hand or be lulled into a false sense of security. In short, you lack the guidance of an experienced physician who can properly explain your results to you.

Another problem with health fairs is that many of the screening tests shouldn't be done in the first place. Study after study has shown that a battery of costly screening tests, indiscriminately done, either turns up no useful information or results in errors in measurement -- and consequently further unnecessary and sometimes risky investigation.

Health fairs are no substitute for a careful, individually tailored history, physical exam and lab testing, done by a physician who knows you and who can go over the meaning of your test results with you.

Jay Siwek, a family physician from Georgetown University, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.

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