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Information about cholesterol

  Lipid disorders
  Blood testing
  Risks and goals
  Treatments:
    Diet
    Exercise
    Medication
  Children
  Glossary

Blood Testing and Evaluation

About Measuring Plasma Cholesterol

Plasma cholesterol can be measured any time of day, before or after eating, to learn the total cholesterol and the HDL-cholesterol.

A measurement that provides triglyceride and LDL-cholesterol levels as well as HDL- and total cholesterol is preferred. This blood sample should be taken after 12 hours without food or drink other than water. People having this test may take their usual medications with water, such as blood pressure pills, which do not contain sugar. Any calories from food, beverages, or even syrupy medications before the test can increase the blood triglyceride content.

The LDL-cholesterol is not usually measured directly. It is calculated using this formula:

LDL-cholesterol = total cholesterol - HDL-cholesterol - triglyceride/5

The formula is useful if the triglycerides are less than 400 mg/dL. For people with unusually high triglycerides, greater than 400, the formula may not be accurate and the LDL-cholesterol should be measured directly.

About Ratios

Sometimes a ratio is provided with the results of a laboratory test. The ratios most frequently given are:

total cholesterol/HDL-cholesterol or LDL-cholesterol/HDL-cholesterol

Ratios do not provide as much information as the measured values themselves. (For example a ratio of 4/1 might mean total cholesterol is 120 and HDL is 30, or it might mean total cholesterol is 300 and HDL is 75. These are two different conditions.)

The ratio is useful when a treatment is given and both the "top" and "bottom" numbers change. Then the ratio shows if there is overall benefit. Lower ratios are better than high ratios.

Other Tests

Other lipid measurements are occasionally performed, especially when there is a family history of heart disease at early ages. Apoprotein A, or "apo A," is associated with HDL-cholesterol. Apo B is associated with LDL-cholesterol. These apoproteins indicate the number of particles carrying HDL or LDL-cholesterol.

Lp(a) is elevated in some families, and increases the risk of developing heart disease. Although Lp(a) is changed little by medication, high levels indicate a need to treat other risk factors more aggressively. Elevation of this number is among the most common reasons for premature atherosclerosis in persons without large elevations in LDL-cholesterol.

Homocysteine is elevated in some families, and is thought to increase the risk of developing heart disease. Homocysteine is improved with adequate B vitamins: folic acid, B-12, and B-6. Folic acid is now supplemented in white flour products such as bread, and is also high in leafy green vegetables and oranges. Vitamin B-12 is provided by all animal foods, but absorption may be decreased in older adults. Vitamin B-6 is most abundant in whole grains, bananas, and potato with skin. When homocysteine is known to be high, B vitamin supplements are usually recommended.

Recently, research attention has been drawn to c-reactive protein, which is elevated during inflammation and infection. Chronically elevated c-reactive protein has been linked to risk of heart disease, but there are many factors involved. It is premature to make treatment decisions for heart disease prevention based on this test.