Is the determination of LDL cholesterol according to Friedewald accurate in CAPD and HD patients?
Lipid abnormalities are a major cause of accelerated atherosclerosis in patients with end-stage renal disease. In many clinical laboratories, the concentration of low density lipoproteins (LDL), the most atherogenic lipoprotein fraction, is estimated by calculating LDL cholesterol according to Friedewald. Hypertriglyceridemia, a common finding in uremic patients, is a main limitation to the use of the Friedewald formula, and the estimation of LDL cholesterol may, therefore, not be reliable in these patients. As accurate quantitation of LDL cholesterol is needed to decide on the initiation of lipid lowering therapy, we have evaluated the accuracy of the Friedewald formula in 171 patients on continuous ambulatory peritoneal dialysis (CAPD), 136 hemodialysis (HD) patients and 887 clinically healthy individuals by comparing it with a combined ultracentrifugation and precipitation 'reference' method. When we excluded sera with total triglycerides above 400 mg/dl [4.56 mmol/l], the Friedewald formula correlated excellently with the reference method; non-parametric correlation coefficients were 0.976, 0.971, and 0.956 in clinically healthy individuals, CAPD and HD patients, respectively. In the control individuals, the Friedewald formula produced slightly lower concentrations of LDL cholesterol than the reference method (means: 142 +/- 40 mg/dl vs 150 +/- 39 mg/dl or 3.68 + 1.04 mmol/l vs. to 3.89 + 1.01 mmol/l, respectively). This was also true in HD patients (means: 145 +/- 51 vs. 146 +/- 49 mg/dl or 3.76 +/- 1.32 vs. 3.78 +/- 1.27 mmol/l, respectively), but not in CAPD patients (means: 165 +/- 50 vs. 162 +/- 47 mg/dl or 4.27 +/- 1.30 vs. 4.20 +/- 1.22 mmol/l). Our data show that, unlike in other forms of secondary dyslipoproteinemia, the Friedewald formula is sufficiently reliable in patients with end-stage renal disease. Much the same, however, as in control individuals, other methods to quantify LDL cholesterol like ultracentrifugation or lipoprotein electrophoresis are recommended when serum triglycerides exceed 400 mg/dl [4.56 mmol/l].