The most common method for calculating LDL cholesterol is the Friedewald formula:
LDL cholesterol = Total cholesterol - HDL cholesterol - (Triglycerides / 5)
This formula assumes certain relationships between triglycerides, VLDL, and LDL. If these assumptions do not hold, especially in individuals with high triglyceride levels, the calculated LDL may not be accurate.
If triglyceride levels are within the normal range, however, other factors that could contribute to the discrepancy are:
- Non-standard Lipoprotein Patterns: The patient might have an atypical lipoprotein pattern that affects the accuracy of the Friedewald calculation.
- Recent Dietary Intake: recent dietary intake, particularly of fatty meals, can affect lipid levels and potentially introduce variability in measurements.
“The performance of LDL cholesterol is influenced by the choice in analyser, the lipid levels (total cholesterol, LDL cholesterol, TG), fasting versus non-fasting samples, the clinical setting and patient profiles, and lipid-lowering therapies including statins and PCSK-9 inhibitors.” In cases where knowing the precise LDL measurement is critical, or where there's a notable discrepancy, relying on direct LDL measurement is advisable (Martins et al., 2023).
In regard to analytical precision, measurement errors, and instrument calibration, Vibrant America Clinical Lab is a College of American Pathologists (CAP)-accredited and Clinical Laboratory Improvement Amendments (CLIA)-certified clinical laboratory. Quality control (QC) procedures are established to identify and eliminate error throughout the pre-analytical, analytical, and post-analytical testing phases. QC methods are continuously updated with the latest laboratory and technology advances. As part of the QC process, the Lab performs daily internal quality controls, maintenance schedules, and calibration checks to validate that test results are precise, accurate, reliable, and reproducible. Results are reported only when lab quality control procedures are passed. Quality control records were assessed for the date of service, and all quality control procedures passed.