Cholesterol

Cholesterol is a type of lipid whose bodily uses include hormone production and cell membrane formation. Cholesterol is not soluble in water, and is carried through the bloodstream bound to proteins, resulting in ‘lipoprotein complexes’ of varying sizes, the most pertinent of which are low density lipoprotein (LDL) and high density lipoprotein (HDL).

LDL is sometimes known as 'bad' cholesterol because it is associated with atherosclerosis or 'hardening of the arteries', which can lead to angina, heart attack and stroke. HDL is sometimes known as 'good' cholesterol because it clears cholesterol from the arteries to the liver, where it is removed from the body.

Monitoring cholesterol levels includes measuring the levels of LDL, HDL, and total cholesterol (TC) - the sum of LDL and HDL. High TC and LDL levels in the blood (TC and LDL), and low levels of HDL, are associated with an increased risk of hardening and narrowing of the arteries and heart disease.

Low levels of cholesterol are often seen among people with advanced HIV disease. However, research has shown that people on protease inhibitor therapy have significantly higher levels of total cholesterol when compared with HIV-positive people not on protease inhibitors.

Total cholesterol levels (range):

• Average: 2.3 to 5.8 mm (88 - 224mg/dl).
• High: 5.8 to 6.9 mm (224 to 266mg/dl).
• Very High: over 6.9 mm (over 266mg/dl).

To convert into United States cholesterol measurements (mg/dl), multiply mm by 38.6. To convert United States measurements into mm, multiply by 0.0259.

In the United Kingdom the average adult cholesterol level is around 5.6 mm, but an optimal level is considered to be less than 5.2 mm (200mg/dl).

HDL ('good' cholesterol) levels:

• Normal range in women: 1.0 to 2.0 mm (38 to 77mg/dl).
• Normal range in men: 0.7 to 1.6 mm (27 to 62mg/dl).

British HIV Association guidelines recommend that individuals with total cholesterol above 6.5mm or an LDL to HDL cholesterol ratio of greater than 4 should consider a number of interventions:

• Switching to a PI-sparing regimen if taking your first regimen.
• Stop smoking.
• Increase exercise levels, reduce intake of saturated fat and look at diet with advice from dietitian.
• Treatment with pravastatin (40mg a day) or atorvastatin (10mg a day).

The target for total cholesterol is 5.5mm or less (212mg/dl), with a target LDL to HDL ratio of 3 or less.

The American National Cholesterol Education Program (NCEP) has graded target LDL levels according to a person's risk of heart disease. For people with no risk factors or one risk factor for heart disease, the target is 4.1mm. For people with two or more risk factors, the target is 3.3mm. For people with heart disease, the target is 2.5 mm. Key risk factors include: smoking, high blood pressure, diabetes, family history of heart disease, age over 45 years in men, post-menopause in women.

The Quebec Cardiovascular Study found that the ratio of total cholesterol to HDL cholesterol was superior to the LDL:HDL ratio in predicting cardiovascular events, but this formula has not been adopted universally. ¹