Evaluation of five methods for determining low-density lipoprotein cholesterol (LDL-C) in hemodialysis patients(1).
OBJECTIVE
Current recommendations for the management of dyslipidemia are largely based on the concentration of LDL-C. Most clinical laboratories estimate the concentration of LDL-C by the recommended routine method, the equation of Friedewald, in specimens from fasting subjects and with TG concentrations < 4.52 mmol/L. Because of the limitations of the Friedewald calculation, direct methods for an accurate quantification of LDL-C are needed.


METHODS
In the present study we evaluated the accuracy of the following 5 different procedures for LDL-C in 98 patients on hemodialysis: the Friedewald equation, where LDL-C is calculated from HDL-C, measured either by the precipitation procedure with dextran sulfate-Mg(2+) (Method 1), or by a direct HDL-C assay (Method 2), the Direct LDL assay (Method 3), the homogeneous N-geneous LDL assay (Method 4) and the calculated LDL-C values deriving from the ApoB based equation: 0.41TC - 0.32TG + 1.70ApoB - 0.27, (Clin Chem 1997;43:808-815) (Method 5).


RESULTS
All five LDL-C methods were found to be in good agreement with ultracentrifugation/dextran sulfate-Mg(2+) precipitation with the coefficients of correlation of the assays to ranging between 0.93-0.95. However, significant differences in the mean values and biases vs. the reference method were observed. The Friedewald equation and the Direct assay were less affected by high LDL-C levels, and they presented higher sensitivity and higher negative predictive value. The N-geneous assay and the ApoB derived calculation were less affected by high triglyceride levels, and they presented higher specificity and higher positive predictive value. At the diagnostic LDL-C level of 3.37 mmol/L, both Friedewald calculations correctly classified 82/92 patients; Direct assay 86/98; N-geneous assay 88/98; and ApoB derived calculation 88/98. At the diagnostic LDL-C level of 2.98 mmol/L, Friedewald calculations (Method 1 and Method 2) correctly classified 82/92 and 81/92 patients, respectively; Direct assay (LDL-3) 87/98; N-geneous assay (LDL-4) 91/98; and ApoB derived calculation (LDL-5) 91/98.


CONCLUSIONS
Among hemodialysis patients, who commonly present "average" LDL-C concentrations and high TG levels, the N-geneous assay and the apoB derived calculation seem to yield more acceptable results for the estimation of LDL-C.
Bairaktari
E
E
Laboratory of Biochemistry, University of Ioannina, 450 00, Ioannina, Greece. ebairakt@cc.uoi.gr
Elisaf
M
M
Tzallas
C
C
Karabina
S A
SA
Tselepis
A D
AD
Siamopoulos
K C
KC
Tsolas
O
O
D001055:Apolipoproteins B / Q000097:blood*; D015982:Bias; D002784:Cholesterol / Q000097:blood; D008076:Cholesterol, HDL / Q000097:blood*; D008078:Cholesterol, LDL / Q000097:blood*; D006801:Humans; D016014:Linear Models; D011237:Predictive Value of Tests; D011933:Reagent Kits, Diagnostic; D006435:Renal Dialysis; D051437:Renal Insufficiency / Q000097:blood*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014280:Triglycerides / Q000097:blood
D001055:Apolipoproteins B; D008076:Cholesterol, HDL; D008078:Cholesterol, LDL; D011933:Reagent Kits, Diagnostic; D014280:Triglycerides; D002784:Cholesterol