Friedewald equation underestimates low-density lipoprotein cholesterol at low concentrations in young people with and without Type 1 diabetes.
OBJECTIVE
Although the limitations of the Friedewald-calculated serum low-density lipoprotein cholesterol (LDL-C) are well recognized, many diabetes and lipid guidelines propose LDL-C as a therapeutic target. The validity of calculated LDL-C in people with Type 1 diabetes (T1DM) is uncertain and the use of alternatives such as non-high-density lipoprotein cholesterol (non-HDL-C) or apolipoprotein measurement unexplored. We have therefore measured LDL-C with the designated reference method and examined some of the potential sources of such bias, including plasma concentrations of other lipids and apolipoproteins.


METHODS
Seventy-four people with T1DM and 80 healthy control subjects were recruited. Fasting samples were collected for analysis of lipid profiles by a beta-quantification (BQ) reference method and by routine laboratory methods including direct HDL-C and calculation of LDL-C using the Friedewald formula.


RESULTS
Overall, Friedewald LDL-C was 0.29 +/- 0.02 (mean +/- SE) mmol/l (P < 0.001) lower in the two groups than by the BQ method. This resulted in misclassification of approximately 50% of people with a calculated LDL-C < 2.0 mmol/l. Overestimation of HDL-C by the routine assay [0.08 +/- 0.01 mmol/l (P < 0.001)] accounted for approximately 28% of the error in calculation of LDL-C and the remainder appeared to be as a result of triglyceride in lipoprotein particles other than very-low-density lipoprotein (VLDL). Correlation of non-HDL-C with apolipoprotein B was better than LDL-C with apolipoprotein B for both assays in both diabetic and non-diabetic populations.


CONCLUSIONS
Calculated LDL-C is unsuitable as a therapeutic target in T1DM. Consideration should be give to the greater use of apolipoprotein B or non-HDL-C in clinical practice.
Sibal
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L
Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK. latikasibal@hotmail.com
Neely
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Jones
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D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001055:Apolipoproteins B / Q000378:metabolism*; D008078:Cholesterol, LDL / Q000378:metabolism*; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism* / Q000503:physiopathology; D005215:Fasting / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results; D014280:Triglycerides / Q000378:metabolism*; D055815:Young Adult
D001055:Apolipoproteins B; D008078:Cholesterol, LDL; D014280:Triglycerides