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* The Friedewald formula for the calculation of low-density lipoprotein cholesterol (LDL-C) values is fairly accurate provided the triglyceride value is less than 400 mg/dL. It is not clear whether the estimation is also valid in the presence of low triglyceride and high cholesterol levels. We describe herein a patient with a low triglyceride value of approximately 50 mg/dL, a high cholesterol level, and a discrepant LDL-C level. The LDL-C level using the Friedewald calculation turned out to be much higher than the LDL-C level using direct measurement. We, therefore, suggest that in the presence of low triglyceride and high cholesterol levels, the LDL-C level should be measured directly instead of using the Friedewald calculation.
(Arch Pathol Lab Med. 2001;125:404-405)
Hyperlipidemia leads to arthrosclerosis and an increased risk of coronary heart disease (CHD).1,2 Blood lipids, such as total cholesterol (CH), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), and especially low-density lipoprotein cholesterol (LDL-C), become increasingly important in the diagnosis and management of CHD and related diseases. Epidemiological, autopsy, and animal studies have firmly established that a high LDL-C level is arthrogenic.4 The National Cholesterol Education Program, Adult Treatment Panel II (NCEP ATP II) in 1993 classified an LDL-C level of 160 mg/dL or more as a high-risk level, a value between 130 and 159 mg/dL as a borderline value, and a level of less than 130 mg/dL as optimal.1
Currently, most clinical laboratories are using the Friedewald estimation to calculate LDL-C values, ie, LDL-C (calc.) = CH - HDL-C - (TG/5).5 The estimation is fairly accurate provided the TG level is less than 400 mg/dL. We have also observed in our own setting that the LDLC (calc.) values matched closely with direct measurements (unpublished data). In the presence of rare type 3 hyperlipoproteinemia, or if the TG level exceeds 400 mg/dL, the LDL-C (calc.) is no longer reliable and should be measured directly or the result would be erroneously lower.6 We report herein a different type of potential error in the calculation of LDL-C levels. In this case, because of an unusually low TG level, the LDL-C (calc.) level was much higher than the value from direct measurement.
PATIENT AND METHODS
Our patient was a 63-year-old man in good health who recently completed a routine...