Direct clearance method for LDL cholesterol

1st April 2013

Many laboratories do not analyse LDL directly but simply calculate LDL using the Friedewald equation. The Friedewald equation enables the estimation of LDL cholesterol when triglyceride and HDL levels are known however it has known limitations and is only accurate when triglyceride levels are below 400mg/dl, chylomicrons are absent and the sample does not contain beta-VLDL. Research shows at triglyceride levels more than 250mg/dl over 20 per cent of samples are mis-estimated using Friedewald calculation. Due to these limitations the National Cholesterol Education Programme (NCEP) recommend the direct measurement of LDL cholesterol.

The preferred ultracentrifugation method for LDL determination allows for the selection of specific types of lipoproteins based on their density. Although highly accurate ultracentrifugation methods are not routinely used as they are time and labour consuming, difficult to automate and require specialised equipment which many laboratories do not have.

To overcome the limitations of the Friedewald equation and the ultracentrifugation method Randox have developed a clearance method for the direct measurement of LDL cholesterol. Unlike most commercially available direct LDL assays the Randox advanced reagent formulation enables the rapid clearance of turbidity resulting in reduced interference from bilirubin and triglycerides. The assay works by removing all non-LDL components in the first step of the reaction enabling LDL cholesterol to be accurately and specifically measured in the second step.

Despite being based on the clearance method the detergents and buffering systems used in most other direct assays vary leading to significant differences in assay performance.

Further benefits of the Randox direct clearance LDL assay include excellent correlation to the ultracentrifugation method with a correlation coefficient of 0.99, the availability of fully automated applications for a wide range of clinical analysers, excellent onboard stability and reduced labour, time and consumable costs. Furthermore all reagents are liquid ready to use eliminating the risk of reconstitution errors, potential contamination and bottle to bottle variations.

Randox can also provide high quality reagents covering the full lipid profile including: HDL Cholesterol; sLDL Cholesterol; Total Cholesterol
Triglycerides; Lipoprotein (a); Apolipoprotein A-1, A-II, B, C-II, C-III and E.

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