A total-cholesterol test will examine all the blood fats, including the overall cholesterol level, the LDL (low-density lipoproteins, or ‘bad’ cholesterol), HDL (high-density lipoproteins, or ‘good’ cholesterol), triglycerides (the form of fat that transports and stores energy derived from food), plus several other varieties of fats. However, these days, most cholesterol tests concentrate only on LDL cholesterol.

What does the test consist of? It requires a relatively straightforward blood test. You must fast for 9-12 hours before the test, and only water should be drunk during the fast, as even tea or coffee can affect results. A tourniquet is applied to your arm, so that the lower veins pool with blood, and the blood sample is drawn from a vein either on the inside of the elbow or the back of the hand.

All tests for blood fats (or lipids, as they are known in medicalspeak) are measured in terms of milligrammes per deciliter of blood (mg/dL). A total cholesterol count of less than 200 mg/dL is considered acceptable. The current medical wisdom is that the higher the cholesterol count, the greater the risk of heart disease or atherosclerosis (fat-clogged arteries). If your levels are over 240 mg/dL, you are believed to have nearly twice the risk of developing heart disease compared with someone within the normal range. In Europe, the patients’ test results are given in SI (Système International) units. For cholesterol, they are given as mmol/L (1 mmol/L = 38.5 mg/dL). Basically, a healthy person should have a cholesterol level of less than 5.2 mmol/L and a triglyceride level of 15 g/L (1 g/L = 10 mg/dL).

What is considered a high count? The words ‘ high cholesterol’ inspire a feeling of dread in all of us as something akin to a death sentence. The (largely unsubstantiated) view is that high LDL cholesterol may be the best predictor of heart disease. The current medical opinion is that if you have no other risk factors, your LDL count should be below 160 mg/dL. People with one or more risk factors should aim for even lower levels - at below 100 mg/dL for those with heart or vascular disease or diabetes, or below 130 mg/dL for those with two or more heart-disease risk factors (such as high blood pressure, smoking, a family history of heart disease, or being over 45 (men) or over 55 (women).

A high LDL is thought to be countered by high HDL, and vice versa. HDL levels of 60 mg/dL or higher are thought to counteract other risk factors whereas HDL levels below 40 mg/dL themselves become a risk factor.

Even if you have low LDL- and high HDL-cholesterol levels, high triglycerides may still put you at risk. An acceptable triglyceride level is thought to be less than 150 mg/dL.

Is the test accurate? Not particularly. A vast array of conditions can result in an inaccurate test.

One problem is the inherent inaccuracy of the test itself. According to one study, 70 per cent of the samples analysed showed evidence of bias in computing the results (Arch Pathol Lab Med, 1993; 117: 393-400). The equipment used in the analysis may also be inaccurate. In a study of eight such devices, one was judged completely unacceptable, and every one of the remaining seven had drawbacks (Health Devices, 1990; 19: 343-71).