Cardiovascular Risk Factors / Randox News

Variability in the measurement of lipoprotein (a)

High levels of lipoprotein (a) could lead to coronary heart diseaseWhat is Lipoprotein (a)?

High levels of lipoprotein (a) are associated with an increased risk of developing coronary heart disease, cerebrovascular disease, atherosclerosis, thrombosis or stroke. Lp(a) is of particular use in assessing the risk of cardiovascular disease in specific populations as it is genetically determined and is known to vary with ethnic populations.

Lp(a) is an LDL like particle with a molecule of Apolipoprotein B-100 linked by a disulphide bridge to Apolipoprotein (a). The apo(a) component is similar to plasminogen in terms of structure and competes with plasminogen for binding sites resulting in reduced fibrinolysis and the formation of blood clots. Lp(a) is also thought to speed up the process of atherosclerosis by binding LDL, calcium and other components into an atherosclerotic plaque on the blood vessel wall. This dual action of Lp(a) explains its role in the promotion of cardiovascular disease.

Apolipoprotein (a) size related bias

The plasma concentration of Lp(a) varies greatly from person to person due to the apo(a) component. Apo(a) is unique in that it is extremely heterogeneous in size; it is made up of a variable number of repeat structures known as kringles. The size heterogeneity of apo(a) is due to the kringle 4 domain and the kringle 4 type 2 domain in particular which can be present in a variable number of repeat copies ranging from 10 to more than 50. These variable sizes are called apo(a) isoforms and account for the differences in Lp(a) concentration.

The use of Lp(a) as an independent risk factor for cardiovascular disease risk has been impeded by the lack of internationally accepted standardisation and the fact that many commercial Lp(a) methods suffer from apolipoprotein (a) size related bias.

The size heterogeneity of apo(a) affects to varying degrees the outcome of many commercially available Lp(a) kits as the antibodies employed react specifically with the repeat sequences giving different results depending on the number of repeats.

Where size related bias is observed, the more repeat sequences the more antibody binds resulting in a greater immunoturbidimetric signal and an overestimated result. Similarly in samples containing a small apo(a) molecule the Lp(a) result will be underestimated.

With Randox there is no size related bias as the antibody detects the complete Lp(a) molecule providing consistent and correct results.

Why use the Randox Lipoprotein (a) kit?

The Randox liquid ready to use Lp(a) kit provides a highly sensitive and specific method for the detection of Lp(a) in serum and plasma, furthermore it is one of the only methods to exhibit minimum apo(a) size related bias.

The antibody used in the Randox method detects the complete Lp(a) molecule providing accurate and consistent results. Research has documented and shown the Randox method to be one of only few to exhibit minimum size related bias. The International Federation of Clinical Chemistry (IFCC) have conducted studies which clearly highlight the extent of the problem in other commercially available products and now recommend laboratories use tests from suppliers who do not suffer from apo(a) size related bias.

Not only is the Randox Lp(a) kit robust against apo(a) size heterogeneity it is also standardised to the WHO/IFCC reference material SRM 2B and is closest in terms of agreement to the ELISA reference method. Other benefits of the Randox Lp(a) kit include:

  • Liquid ready to use reagents
  • Excellent stability – open vial stability of 30 days on board the analyser at 10oC
  • Dynamic assay range 3 – 90 mg/dl
  • Excellent precision – within run CVs <3%
  • No sample preparation required
  • Limited interference from Intralipid®, Bilirubin, Haemoglobin, Ascorbic Acid, Triglycerides, Plasminogen and Apolipoprotein B
  • Antigen excess effects are not noted up to 341 mg/dl
  • Dedicated or multi-analyte controls and calibrators available
  • Fully automated applications available for a wide range of clinical analysers

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About Randox

Headquartered in the United Kingdom, Randox Laboratories Ltd. is a market leader within the in vitro diagnostics industry, manufacturing high quality diagnostic products for laboratories worldwide. Our extensive product portfolio offers complete solutions within the fields of clinical chemistry, cardiology, forensic toxicology, veterinary, drug residues, life sciences, oncology, molecular diagnostics and internal and external quality control. Our goal is to ‘revolutionise healthcare through continuously improving diagnostic solutions.’ We continue to achieve this year after year due to our commitment and significant re-investment in Research and Development. Our innovative approach to diagnostics allows us to develop revolutionary products, specifically designed to provide more efficient, higher quality and reliable results, ensuring patients receive the right diagnosis at the right time.

 

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