Objectives: To evalate compare the calculated LDL determined by the Friedewald formula when Tg < 200 mg/dL, 200-399 mg/dL, and > 400 mg/dL against a direct method.
Material and Method: Samples from 202 participants (122 males, 80 females, aged 20-87 years old) were determined for cholesterol, triglyceride (Tg), high-density lipoprotein (HDL), and low-density lipoprotein (LDL) at Department of Laboratory Medicine, King Chulalongkorn Memorial Hospital (KCMH). LDL was determined by Friedewald formula and a direct method.
Results: Intra-assay and inter-assay precisions at Tg < 200 mg/dL, 200-399 mg/dL, > 400 mg/dL of calculated LDL and direct LDL were 4.80%, 3.29%, 20.37%, 4.86, 8.42%, 8.32%, 2.11%, 1.79%, 3.99%, 2.36%, 2.41% and 6.16%, respectively. The mean absolute biases calculated for calculated LDL against direct LDL at Tg < 200 mg/dL, 200-399 mg/dL, > 400 mg/dL and for total samples were 4.70%, 11.73%, 63.65%, and 7.46%, respectively. Linear regression analysis for calculated LDL vs direct LDL for total samples and grouped as Tg < 200 mg/dL, 200-399 mg/dL, and > 400 mg/dL were 0.9190, 0.9796, 0.9440, and 0.7910, respectively. Intraclass correlation coefficient (ICC) at 95% confidence interval of calculated LDL against direct LDL at Tg < 200 mg/dL, 200-399 mg/dL, > 400 mg/dL and for total samples were 0.963, 0.930, 0.767, and 0.889, respectively.
Conclusion: The present data suggested that direct LDL is superior over calculated LDL in terms of precision and accuracy. The present study supported that at Tg > 400 mg/dL calculated LDL should not be used and the traditional cutoff of Tg < 400 mg/dL for using Friedewald formula should be revised. In addition, regarding patient convenience, financial reason, and precision and accuracy of analytical method, direct LDL is recommended when Tg > 200 mg/dL.

Keywords: Friedewald formula, Calculated LDL, Direct LDL