The evaluation of the direct method for the LDL-cholesterol.

Abstract

Low density lipoprotein (LDL) is the major carrier of cholesterol in human plasma and elevated levels are associated with a higher risk for the formation of atherosclerotic plaques. The quantification of LDL is of outmost importance in the choice of treatment and dosage for lipid lowering drugs. Nowadays it is becoming even more important in life assurance schemes since an elevated value of LDL-cholesterol would increase the cost of such schemes. There are many different methods for the quantification of LDL. The Friedewald's equation is the most widely used method since it does not require any reagents and gives reliable results under normal lipid profile values. Problems arise when the triglycerides value exceeds 4.5mmoVl due to the fact that this equation is no longer reliable and gives erroneous results in such cases. Other methods are available. However they are either to laborious or not cost effective. The objectives of this study were to evaluate the details of the Randox Direct method for LDL-cholesterol itself and to determine the conditions for the replacement of the current Friedewald's equation. The study was conducted in 2 different laboratories using the Hitachi's 917 as the main analyzer. The Sysmex haematology analyser was used for the estimation of haemoglobin which was used as part of the tests used to evaluate the method. The study was divided into 2 main parts; the first part being kit evaluation and the second patient testing. The total number of samples analysed including the controls was 1473. The reproducibility of the direct method for LDL-cholesterol was tested and the mean result obtained for the 100 samples tested was 1. 5854 with a standard deviation II of ±0.005 and a coefficient of variation of0.31 thus showing that the method is very reproducible. Regarding sensitivity testing the method is sensitive up to a concentration of 0.03mmol/L of LDL-cholesterol. For the assessment of sample storage this study proved that LDL-cholesterol is statistically stable for more than 2 weeks at a temperature of -l5°C. Regarding the assessment of lipaemic samples the direct LDL-cholesterol method is affected statistically even by a triglycerides concentration of7.80mmol/L. However the difference in LDL-cholesterol between triglycerides concentrations of 7.8 to 17.2mmol/L is of only 0.032mmol/L clinically insignificant difference. Regarding the interferences caused by haemolysis the method is affected statistically even by a haemoglobin concentration of 1.Og/dl. Direct LDL-cholesterol estimation was applied to various populations with the following results. Regarding patient testing in the lipid clinic population (n=130) a highly statistical significant difference (p =<0.001) was obtained when comparing the calculated with the direct WL-cholesterol. For the diabetic clinic population (n=108) a highly statistical significant difference (p =<0.001) was obtained when comparing the calculated with the direct LDL-cholesterol. For the general population (n=274) a highly statistical significant difference (p =<0.01) was obtained when comparing the calculated with the direct LDL-cholesterol. For the paediatric population (n=9) an insignificant statistical difference (p = 0. 732) was obtained when comparing the calculated with the direct LDL-cholesterol. For the population having triglycerides values exceeding the 4.5mmol/L (n=30) a highly significant statistical difference (p =<0.001) was obtained when comparing the calculated with the direct LDL-cholesterol. For the population having cholesterol values exceeding the 5mmol/L and triglycerides values below the 1mmol/L (n=23) an insignificant statistical difference (p =0.065) was obtained when comparing the calculated with the direct LDL-cholesterol. In consulting the results obtained the Randox Direct method for the estimation of LDL-cholesterol performed well in all the tests. However with regards to the general Maltese patients the test should be used in patients having triglycerides values exceeding the 4.5mmol/L since such patients have their LDL-cholesterol result omitted out and thus increasing the cost effectiveness of the test by 100%.