Cholesterol Test Health Article

Description

The cholesterol test requires a sample of the patient's blood. Fasting before the test is required to get an accurate triglyceride and LDL level. The blood is withdrawn by the usual vacuum tube technique from one of the patient's veins. The blood test takes between three and five minutes.

Preparation

Patients who are scheduled for a lipid profile test should fast (except for water) for 12–14 hours before the blood sample is drawn. If the patient's cholesterol is to be fractionated, he or she should also avoid alcohol for 24 hours before the test.

Patients should also stop taking any medications that may affect the accuracy of the test results. These include corticosteroids, estrogen or androgens, oral contraceptives, some diuretics, haloperidol, some antibiotics, and niacin. Antilipemics are drugs that lower the concentration of fatty substances in the blood. When these are taken by the patient, blood testing may be done frequently to evaluate the liver function as well as lipids. The patient's doctor will give the patient a list of specific medications to be discontinued before the test.

Aftercare

Aftercare includes routine care of the skin around the needle puncture. Most patients have no aftereffects, but some may have a small bruise or swelling. A washcloth soaked in warm water usually relieves any discomfort. In addition, the patient should resume taking any prescription medications that were discontinued before the test.

Risks

The primary risk to the patient is a mild stinging or burning sensation during the venipuncture, with minor swelling or bruising afterward.

Normal results

The "normal" values for serum lipids depend on the patient's age, sex, and race. Normal values for people in Western countries are usually given as 140–220 mg/dL in adults, although as many as 5% of the population has TC higher than 300 mg/dL. Among Asians, the figures are about 20% lower. As a rule, both TC and LDL levels rise as people get older.

Some doctors prefer to speak of "desired" rather than "normal" cholesterol values, on the grounds that "normal" refers to statistically average levels that may still be too high for good health. Desirable values are as follows:

• Total cholesterol (TC): less than 200 mg/dL
• HDL cholesterol: 40–70 mg/dL in males, 40–80 mg/dL in females
• LDL cholesterol: less than 130 mg/dL
• TC/HDL ratio: under 4.0 in males, 3.8 in females.

Abnormal results

It is possible for blood cholesterol levels to be too low as well as too high.

Abnormally low levels

TC levels less than 160 mg/dL are associated with higher mortality rates from cancer, liver disease, respiratory disorders, and injuries. The connection between unusually low cholesterol and increased mortality is not clear, although some researchers think that the low level is a secondary sign of the underlying disease and not the cause of disease or death.

Low levels of serum cholesterol are also associated with malnutrition or hyperthyroidism. Further diagnostic testing may be necessary in order to locate the cause.

Abnormally high levels

Prior to 1980, hypercholesterolemia (an abnormally high TC level) was defined as any value above the 95th percentile for the population. These figures ranged from 210 mg/dL in persons younger than 20 to more than 280 mg/dL in persons older than 60. It is now known, however, that TC levels over 200 mg/dL are associated with significantly higher risk of CAD. Levels of 280 mg/dL or more are considered elevated. Treatment with diet and medication has proven to successfully lower risk of heart attack and stroke.

Elevated cholesterol levels may also result from hepatitis, blockage of the bile ducts, disorders of lipid metabolism, nephrotic syndrome, inflammation of the pancreas, or hypothyroidism.

BOOKS

Baron, Robert B., and Warren S. Browner. "Lipid Abnormalities." In Current Medical Diagnosis and Treatment, 1998. 37th ed. Ed. Stephen McPhee, et al. Stamford: Appleton & Lange, 1997.

"Laboratory and Reference Guides." In The Merck Manual of Diagnosis and Therapy. 16th ed. Ed. Robert Berkow. Rahway, NJ: Merck Research Laboratories, 1992.

Sobel, David S., and Tom Ferguson. The People's Book of Medical Tests. New York: Summit Books, 1985.

Rebecca J. Frey