Lipoprotein (a)

Lp(a) particles are heterogeneous with a molecular weight of 280-700 kDa. They consist of ApoB100 linked by a single disulphide bridge to Apo(a), a highly glycosylated hydrophilic protein with structural homology to plasminogen. This homology suggests that Lp(a) may be associated with thrombotic and atherosclerotic processes.

The particles have a kringle and a protease domain. The kringle domain has 11 kringle types, ten (K4 type 1and 3) of which are similar to each other and to kringle 4 of plasminogen. Kringle K4 type 2 exists as 3-40 multiple repeats, which accounts for the size heterogeneity; Apo (a) isoforms vary from 187 kDa when 12 K4 domains are present to 662kDa when there are 50 K4 domains.

The serum concentration of Lp(a) is principally genetically determined and may be an independent risk factor for development of atherosclerosis. Concentrations vary widely. Plasma Lp(a) concentrations above 0.3g/L, despite the presence of a normal cholesterol, confer a two fold increased risk for development of coronary heart disease. The risk is 8-fold if LDLC and Lp (a) are both elevated.

Since plasma Lp(a) concentrations are principally genetically determined, lifestyle changes, or treatment with statins or fibrates are ineffective, although niacin or nicotinic acid may effect a 20% reduction. The finding of a high Lp(a) should stimulate aggressive treatment of more easily modifiable risk factors.

Since no international standard exists, values are method/instrument dependent and results from different laboratories may not be comparable.

Clinical indications:
General population screening is not recommended.
Measurement may be useful in patients with coronary heart disease, a family history of premature coronary disease, or familial hypercholesterolaemia.

Reference Range:
Less than 0.3 g/L

Patient preparation:
Patients should follow their normal diet for 3 weeks prior to sampling. A fasting sample is preferred, but non-fasting is acceptable. Standardise posture to reduce effect of change in plasma volume – seat the patient for 5 minutes before sampling. Avoid venous stasis – apply tourniquet briefly before inserting the needle and release before drawing the sample.

Sample details:
EDTA plasma or serum (min. vol. 0.5ml).
Stable 4 days at 4°C, 2months at -20°C
Transport – First Class Post (avoid weekends)

Information required:
Age, sex, NHS/Hospital No.

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