When can LDL not be calculated?

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Multiple Choice

When can LDL not be calculated?

LDL is typically estimated from the Friedewald equation, which assumes a stable relationship between triglyceride–rich lipoproteins and VLDL cholesterol (VLDL-C ≈ TG/5). This works well only when triglycerides are not extremely high and there aren’t interfering particles like chylomicrons. When triglycerides are very elevated—generally above about 4.52 mmol/L (400 mg/dL)—and chylomicrons are present, the TG-based estimate of VLDL-C becomes unreliable, so LDL cannot be calculated accurately using the standard equation. In such cases, direct measurement of LDL or using alternative methods is required. Normal or low triglycerides with no interfering lipoproteins still allow the calculation, and an elevated HDL level by itself does not prevent it.

LDL is typically estimated from the Friedewald equation, which assumes a stable relationship between triglyceride–rich lipoproteins and VLDL cholesterol (VLDL-C ≈ TG/5). This works well only when triglycerides are not extremely high and there aren’t interfering particles like chylomicrons. When triglycerides are very elevated—generally above about 4.52 mmol/L (400 mg/dL)—and chylomicrons are present, the TG-based estimate of VLDL-C becomes unreliable, so LDL cannot be calculated accurately using the standard equation. In such cases, direct measurement of LDL or using alternative methods is required. Normal or low triglycerides with no interfering lipoproteins still allow the calculation, and an elevated HDL level by itself does not prevent it.

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