Blood lipids are important in cardiovascular disease because they contribute to the deposition of lipids into the lining walls of arteries that leads to arterial damage (atherosclerosis).

Low-density lipoprotein (LDL) particles are the major carriers of cholesterol in blood, and they tend to deposit cholesterol into artery walls.

High-density lipoprotein (HDL) particles scavenge cholesterol back out of arteries, and protect against atherosclerosis.

The National Heart Foundation recommends that total cholesterol should be less than 5mmol/L. This is lower than the average for the New Zealand population: the level is chosen as an achievable ideal since cardiovascular risk reduces as cholesterol reduces.

The major constituents within total cholesterol are LDL-cholesterol and HDL-cholesterol. While a low total cholesterol is desirable, within that total the higher the HDL-cholesterol the better. HDL-cholesterol should preferably be greater than 1.0 mmol/L. The ratio of total to HDL-cholesterol (often called the "risk ratio") should ideally be less than 4.5.

Another major lipid constituent of blood is triglyceride. It is mostly carried in chylomicrons, which transport absorbed lipids from the gut to the liver, and in very-low-density lipoproteins (VLDL) which carry lipids from the liver to the peripheral tissues. High triglyceride is found in some genetic hyperlipidaemias, and is a risk factor (but not as significant a factor as cholesterol) in cardiovascular disease. Because it is absorbed from food and transported in chylomicrons, triglyceride is much more affected by meals than cholesterol, much of which is synthesised within the body.

To assess triglyceride, a fasting blood specimen is essential. It is easiest to have the test in the morning, and follow it with a late breakfast. You should have had no food and water only to drink (no tea or coffee) for at least 14 hours before the blood test. If you take regular medicines, then you should take them (with water) at the usual time UNLESS you take insulin injections. Insulin should be delayed until after the test, when you will be able to have breakfast.