Limitations of calculated LDL-C (Friedewald method)
One of the limitations of using the the Friedewald-calculated LDL method is that when the trigly is greater than 400 mg/dl the LDL-C is FALSELY LOW
e.g. Patient X: Total cholesterol = 250 mg/dl , HDL = 40 mg/dl, Trigly = 400 mg/dl
Friedewal LDL-C = 250 - (40 - 450/5)
Friedewald LDL-C = 250 - (40 - (-90))
Friedewald LDL -C = 250 - 130
Friedewald LDL-C = 120 mg/dl ( falsely low because of a high denominator)
Which comes to our question - "will direct LDL solve the problem of not being able to report LDL-C values when trigly exceeds 400 mg/dl?"
Sad to say NCEP concluded, in ATP III, that current direct methods ( Genzyme N-Genous LDL, Reference Diagnostic LDL, Roche LDL-C-Plus, Sigma EZ-LDL) also suffer from various inaccuracies when triglycerides is greater than 400 mg/dl.
Source:
1. Nauck M, Warnick GR, Rifai N. Methods for measurement of LDL-cholesterol: a critical assessment of direct measurement by
homogeneous assays versus calculation. Clin Chem 2002; 48:236-54.
2. Miller WG, Waymack PP, Anderson FP, Ethridge SF, Jayne EC. Performance of four homogeneous direct methods for LDL-
cholesterol. Clin Chem 2002; 48:489-98.
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