Synonyms: APO A-1
Related tests: Triglycerides, Total cholesterol, APO B, HDL, LDL, Lipoprotein (a), LDL subclasses.
Clinical significance
Apolipoprotein A1 is the main structural protein of HDL (high-density lipoprotein); the role of Apo A1 is not only to allow esterified cholesterol (and, to a much lesser extent, triglycerides) to be transported in the blood, but also to recognise the specific HDL receptors present on the membranes of some cells.
Raised serum Apo A1 can be seen in familial hyperalphalipoproteinaemia and with weight loss.
Reduced serum Apo A1 can be seen in the following conditions: familial hypoalphalipoproteinaemia, hypertriglyceridaemia, poorly controlled diabetes, hepatocellular disorders, cholestasis, nephrotic syndrome and chronic kidney failure.
The ratio of Apo A1 to Apo B (the main apolipoprotein of LDL) can be an indirect index of the ratio of HDL to LDL, and therefore of HDL cholesterol to LDL cholesterol.
Clinical indications
Assessment of the risk of ischaemic cardiovascular disease
Sample type
The patient must have a blood sample taken
Preparation
You must fast for 12 hours; a small amount of water is allowed. You must have been standing or sitting upright for at least 30 minutes.
In the days before the blood test, you are advised to keep to your usual diet as far as possible.
Notes
A true increase in serum Apo A1 can be caused, in vivo, by treatment with carbamazepine, oestrogens, statins, phenobarbital, phenytoin or oral contraceptives, as well as by weight loss in obese people, physical exercise and moderate alcohol consumption.
A true decrease in serum Apo A1 can be caused, in vivo, by treatment with androgens, beta-blockers or diuretics, as well as by smoking and diets high in saturated fat and cholesterol.
The limitation of Apo A1 is that it is an indirect index: it gives no direct information on the size of LDL particles (see LDL subclasses).