LIPOPROTEIN (a)
ITxM Diagnostics is pleased to offer a quantitative
assay for lipoprotein(a) (Lp(a)) for the assessment of
risk for coronary heart disease (CHD) in specific
populations.
BACKGROUND
Lipoprotein (a) is a cholesterol-rich
lipoprotein, similar to low-density lipoprotein (LDL)
and found in human plasma. This sticky molecule is
made up of an apo B and apo(a) that binds to fibrin, LDL
receptors, and plasminogen binding sites. Lp(a)
inhibits fibrinolysis by competition with plasminogen
for fibrin. Additionally, Lp(a) can bind to the
endothelium and arterial wall resulting in localized
cholesterol accumulation forming atherosclerotic plaques
promoting clogging of arteries.
Lp(a) levels are genetically determined
and the normal range of Lp(a) in humans varies by ethnic
population. The normal range is the same in Caucasian
and Asian populations. However people of African
descent have demonstrated normal ranges that are twice
higher than Caucasian populations while Native American
and Mexican populations have normal ranges that are half
of the Caucasian population.
Lp(a) has been referred to as a
predictor of premature atherosclerotic vascular
disease. Excess Lp(a) concentrations have been
associated with an increased risk of coronary artery
disease (CAD), and premature CAD in Caucasian males.
The variability of Lp(a) levels by ethnic population
requires careful interpretation of results based on a
knowledge of the patient and other cardiac risk factors
which may be present.
METHODS
Lp(a) testing uses an Enzyme Linked
Immunosorbant Assay (ELISA) format. The test utilizes
antibodies that bind to the apo(a) moiety of Lp(a) to
capture the protein from the sample. The concentration
of Lp(a) mass (mg/dL) is quantitatively determined by
comparison of the absorbance of the sample with a
standard curve prepared with known concentrations of
Lp(a).
CLINICAL APPLICATION
The association of elevated levels of Lp(a) with risk of myocardial infarction(MI) has been
documented and has substantiated Lp(a) to be an
independent risk factor for MI (1,2). Almost all
cross sectional and retrospective studies on Caucasian
men have shown an increased risk of coronary disease
and stroke or peripheral and cerebrovascular
atherosclerotic disease associated with plasma Lp(a)
values greater than the 80th percentile
(>300 mg/L)(3). An elevated Lp(a) coupled with a low
HDL puts a patient at 8.3 times the relative risk for
CHD (4). Clinical studies have shown elevated levels
of Lp(a) to be associated with stenosis and restenosis
after percutaneous transluminal coronary angioplasty
(5,6). Familial studies of patients with premature
CHD suggest that Lp(a) may be an important initiator
and promoter of, as well as an early marker for, the
atherosclerotic process (7,8). Therefore it is
recommended the Lp(a) assay be used in the following
clinical situations:
-
Patients with premature
CHD
-
Patients with peripheral
and/or cerebrovascular atherosclerotic disease
-
Risk assessment of
patients with abnormal lipid studies
HOW TO ORDER
In
order to assure the accuracy of our test results,
plasma should be collected from one (1) blue top
tube. This sample must be spun within one hour of
collection, performing centrifugation for 15 minutes
at 3000 RPM, at a temperature that never exceeds 18oC.
The sample is then frozen at -20oC or less
and shipped on dry ice. It is important that the
plasma be free of platelet contaminants.
The fee for the lipoprotein (a) assay
is $150.00.
TEST CODE: 5653 CPT
CODE: 82172
For further information
call:
412-209-7270 or 1-800 967-9672
REFERENCES
-
Kark JD, Sandholzer C, et al.
Atherosclerosis 98: 1993: 139-151.
-
Hobbs HH, White AL. Curr
Opin Lipidol 10: 1999: 225-236.
-
Kostner G, Avogaro P, et al.
Atherosclerosis (Netherlands) 38: 1981: 51-61.
-
von Eckardstein et al. J
Am Coll Cardiol 37: 2001: 434-439.
-
Solymoss BC, Marcil M, et al. Can J
Cardiol 9: 1993: 30-84.
-
Tenda K, Saikawa T, et al. Jpn Circ
J 57: 1993, 789-795.
-
Bostom AG, Cupples AL, et al. JAMA
1996: 276/7: 544-548.
-
Wald NJ, Law M, et al. Lancet 1994: 343:
75-79
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