Repercusiones clínicas de la utilización de la fórmula de Friedewald para el cálculo del colesterol LDL usando los puntos de corte establecidos por el NCEP

Backround and aim. LDL cholesterol (LDLc) is the main therapeutic target in the management of dyslipidaemia, and the "National Cholesterol Education Program" (NCEP) has established cardiovascular risk categories according to LDLc concentrations, which are used to decide patient treatment. The recommended method for the determination of LDLc (cLDLcdc) combines ultracentrifugation and selective protein precipitation. Because it is cumbersome and needs an ultracentrifuge, the NCEP accepts the use of Friedewald's equation when triglyceride concentrations are < 4.52 mmol/l (400 mg/dl). The aim of this study is to reassess the usefulness and limitations of estimating LDLc by Friedewald's equation (cLDLf) and classifying the results according to serum triglyceride concentrations. Methods. cLDLf and cLDLcdc have been determined in 546 consecutive non-chylomicronemic serum samples. cLDLf accuracy (error < 10%) and its consequences for the correct classification of patients into NCEP risk intervals was assessed according to triglyceride concentrations. Results. A total of 85.9% of the samples with triglyceride concentrations < 3.39 mmol/l (300 mg/dl) showed an error < 10% when compared with the recommended method. This percentage decreased to 47.8% when triglyceride rose above that cut-off point (68% in the triglyceride range 3.39-4.52 mmol/l). Classification into NCEP risk intervals was incorrect in 20.8 and 40% of cases when triglycerides were below or above 3.39 mmol/l, respectively (32% in the interval between 3.39 and 4.52 mmol/l). Conclusions. When triglycerides lie above 3.39 mmol/l (300 mg/dl), Friedewald's equation is highly inaccurate. Thus, until standardised direct LDLc methods are available, the recommended method of LDLcdc should be used when triglycerides exceed this concentration.