Definition This test measures the total amount of cholesterol in the blood. It is generally done together with blood tests that measure a person's HDL cholesterol and LDL, or "bad cholesterol".
Since high levels of cholesterol are often associated with cardiovascular disease, the test is done to evaluate a person's heart disease risk. It may also be ordered to detect disorders of the thyroid gland, kidney or other body organs.
Cholesterol is attached to fatty molecules called lipoproteins, which are carried in the bloodstream. The two major lipoproteins are low-density lipoproteins (LDL) and high-density lipoproteins (HDL). HDL transports excess cholesterol to the liver for excretion in the bile, a liver product that helps with fat absorption and that excretes waste products. It is known as the "good" cholesterol. LDL leaves fatty deposits on the wall of the arteries, a condition called arteriosclerosis, and is known as the "bad" cholesterol. Therefore, the ratio of LDL to HDL is a measure used to evaluate risk for heart disease. A low LDL:HDL ratio means lower risk, and vice-versa.
How is the test performed? A blood sample needs to be taken in order to measure the level of blood cholesterol. The blood is usually drawn from a vein in the forearm or the hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube called a tourniquet is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A very thin needle is gently inserted into a vein and the tourniquet is removed. Blood flows from the vein through the needle and is collected in a syringe or vial. The sample is sent to the laboratory to be analysed. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
What is involved in preparation for the test? Individuals should request specific instructions from their doctors about how to prepare for this test.
What do the test results mean? Normal values for total blood cholesterol range from 3.6 to 7.7 mmols/L (millimoles per litre). The best range is from 3.6 to 5.7 mmols/L.
Abnormally high levels of blood cholesterol may indicate:
pernicious anaemia, which is low red blood cell count from vitamin B12 deficiency
infection
Author: Reviewer: HealthAnswers Australia Medical Review Panel Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia Last Updated: 1/10/2001 Contributors Potential conflict of interest information for reviewers available on request
