Apolipoprotein

Keywords: Lipoprotein(a), Lipoprotein A1, LPA1, ApoA1, Lipoprotein B, LPB, ApoB, Lipoprotein E, LPE, ApoE, Apolipoprotein A1, Apolipoprotein B, Apolipoprotein E

Specimen:

5 mL blood in plain tube.

Genotyping for apo E requires collection of a suitable specimen eg, 5 mL blood in an EDTA tube.

Method:

Immunoassay.

The apolipoproteins usually quantitated are apo A-I, apo B and apo (a); apo E genotyping or phenotyping may also be done.

Reference Interval:

Apolipoprotein A-I and apo A-I: 1.0-1.8 g/L

Apolipoprotein B (apo B): Optimally < 0.9 g/L

Lipoprotein (a) (Lp [a]): Optimally < 0.2 g/L - depends on method.

Application:

Apo A-I and apo B may be measured as an alternative to HDL and LDL cholesterol respectively in the assessment of atherosclerosis risk factors, and may offer better prediction of risk.

Apo B together with LDL cholesterol can be used to define hyperapobetalipoproteinaemia, a condition associated with small dense LDL and increased risk of atherosclerosis.

Lipoprotein (a) is an independent risk factor for atherosclerosis and may be indicated in the assessment of a patient with premature coronary or cerebral arterial disease, especially if there is a suggestive family history.

Apo E genotyping is done in patients with suspected type III Hyperlipidaemia (raised cholesterol and triglycerides).

It can also be used to identify some patients at risk of developing Alzheimer's disease but the ethical implications of such testing remain controversial.

Apo A-I and apo B are very low in Tangier disease and abetalipoproteinaemia (plus hypobetalipoproteinaemia), respectively.

Interpretation:

Decreased apo A-I and increased apo B or Lp (a) are associated with an increased risk of atherosclerosis.

Raised Lp (a) is associated with increased vascular risk.

Homozygous apo E2 may result in type III Hyperlipidaemia.

Homozygous apo E4 may be associated with an increased risk of Alzheimer's disease.

Reference:

Walldius G et al. Lancet 2001; 358: 2026-2033.

Hakim J et al. Clin Cardiol 2002; 25: 193.

Hackam DG, Anand SS. JAMA 2003; 290: 932-940.