Blood cholesterol levels may be referred to as total cholesterol, serum cholesterol or plasma cholesterol. All these terms refer to the concentration of cholesterol in the bloodstream. This will be given in millimoles per litre (mmol/1), and the reading will probably be between 5 and 7.5 mmol/1. The other unit of measurement is milligrams per decilitre (mg/dl); divide this by 38.6 to get a reading in mmol/1, e.g. 213 mg/dl is the same as 5.5 mmol/l.
The HDL:LDL ratio. If your blood sample is sent off to a laboratory your result may well come back with not only the total blood cholesterol figure, but also the breakdown of this figure into the LDL and HDL fractions. For example, you might have a total blood cholesterol of 6.0 mmol/1, with an HDL of 1.2 mmol and an LDL of 4.2 mmol/1. This information is useful as the HDL:LDL ratio is often discussed in conjunction with cholesterol levels.
LDL transports cholesterol from the liver to the peripheral tissues, including the artery walls; there it can become involved in the furring-up process in the arteries that eventually leads to coronary heart disease.
HDL, in contrast, transports cholesterol from the peripheral tissues back to the liver, and seems in some way to be able to remove some of the furring-up that leads to coronary heart disease; a raised HDL level certainly appears to give some protection against coronary heart disease.
Triglycerides. The lab report also gives the fasting triglyceride level of the blood sample. This is of value, as a raised triglyceride level is a good predictor of a number of diseases, although its relevance to coronary heart disease is not so clear at the moment. But if both your cholesterol level and your triglyceride level are raised your doctor will undoubtedly be extremely keen to get you on a low-fat fibre diet in order to try and reduce both these figures.
For various reasons your doctor or you may want to know your blood cholesterol level. You may have a small blood sample taken for laboratory analysis or you may have a fingerprick test.
In a fingerprick test, the tip of a finger is pricked and a drop of blood placed on a chemical-impregnated strip, which is inserted in a machine the size of a typewriter. Three minutes later the result is flashed up. A fingerprick test cannot give the more accurate result provided by a laboratory. Therefore, if such a test indicates you have a raised blood cholesterol level, you should ask your GP for a more detailed laboratory analysis.
You may be required to fast for a minimum of 12 hours before a blood sample can be taken for laboratory analysis. The usual procedure is to give you a morning appointment, and to ask you to have no breakfast before the sample is taken. The reason for this has nothing directly to do with the blood cholesterol level, but concerns another group of lipids (fats) that is measured at the same time. This group, called the triglycerides, is very much affected by what you have eaten over the previous few hours, and an accurate and useful result can only be achieved after such food has been processed and metabolised by the body.
A blood test reveals not only the total cholesterol level, but also the HDL:LDL ratio and the triglyceride level.