If TAG is high, LDL-C is determined using which method?

• A. Beta Quantification
• B. Indirect Calculation
• C. Homogenous Direct Assay
• D. Ultracentrifugation

Answer: (C)

Elevated triglycerides make the commonly used Friedewald calculation unreliable because it estimates VLDL-C from TG/5, and that approximation breaks down when TG levels are high. In that situation, directly measuring LDL-C avoids depending on this estimation and yields a more accurate value.

A homogeneous direct LDL-C assay does just that: it measures LDL-C directly in the serum in a single step, without needing ultracentrifugation or subtraction of other lipoproteins. This makes it the preferred method when triglycerides are elevated.

Beta quantification by ultracentrifugation is accurate but impractical for routine use, and calculating LDL-C indirectly is not trustworthy with high TG. Therefore, a direct homogeneous assay is the best choice.