Does fasting affect Low-Density Lipoprotein (LDL) cholesterol results?

From the Guidelines

Fasting has a minimal impact on LDL cholesterol test results, and non-fasting tests are becoming increasingly accepted in clinical practice. For standard lipid panels, fasting for 9-12 hours before the blood draw has traditionally been recommended, though non-fasting tests are now considered adequate for routine monitoring 1. When you fast, LDL levels may appear slightly lower (by about 2-10%) compared to non-fasting measurements, due to the reduction in triglycerides in the bloodstream, which can affect the calculation of LDL cholesterol using the Friedewald equation 1.

Some key points to consider:

• Non-fasting lipid profiles provide acceptably accurate measures for risk calculation, with small variances in LDL-C levels unlikely to affect classification of risk or therapeutic decisions 1.
• Fasting lipid measures may be necessary if triglyceride levels are greater than 4.52 mmol/L (>400 mg/dL), or if the purpose is to measure or monitor triglyceride levels 1.
• The efficacy of statins is based on a target dose, not lipid levels, and routine monitoring of lipids once a statin is initiated is not recommended, unless adherence is a concern or the patient is receiving high-dose statins 1.
• Non-fasting samples can be used for risk assessment in primary prevention and for assessment of baseline LDL-C levels before the initiation of a statin in primary and secondary prevention, with fasting lipids measured if more precision is necessary 1.

In terms of the impact of fasting on LDL cholesterol levels, studies have shown that:

• Total cholesterol and LDL-cholesterol decreased by 9·1 % and 12·4 %, respectively, after a fasting period 1.
• Fasting can lead to a reduction in triglyceride levels, which can affect the calculation of LDL cholesterol using the Friedewald equation 1.
• Non-fasting LDL measurements can reflect typical daily lipid levels, and are considered adequate for routine monitoring 1.

Overall, the impact of fasting on LDL cholesterol test results is minimal, and non-fasting tests are becoming increasingly accepted in clinical practice. If you're having your cholesterol checked, it's best to follow your healthcare provider's specific instructions about fasting, and to maintain consistency in your fasting status between tests 1.

From the Research

Fasting and LDL Results

• Fasting status can impact lipid measurements, including low-density lipoprotein cholesterol (LDL-C) levels 2
• Studies have shown that fasting samples are independently associated with a higher LDL-C of 4.1 mg/dL and apolipoprotein-B 100 of 2.6 mg/dL, as well as a lower triglyceride (TG) of 21.0 mg/dL and high-sensitivity C-reactive protein of 0.48 mg/dL 2
• The relative difference in LDL-C levels between fasting and non-fasting samples is approximately 3.8% 2
• However, the effect of fasting on LDL-C levels is considered small, with a difference of about 4 mg/dL, and recent guidelines suggest that fasting may not be necessary for lipid measurements 2, 3

LDL Measurement Accuracy

• The accuracy of LDL-C estimation can be affected by fasting status, with novel methods such as LDL-CN performing better in non-fasting samples than the fixed Friedewald estimation 3
• The novel method of LDL-C estimation (LDL-CN) uses a flexible approach to derive patient-specific ratios of triglycerides to very low-density lipoprotein cholesterol, which may confer an accuracy advantage in non-fasting patients 3
• In non-fasting samples, the accuracy of LDL-CN is superior to LDL-CF, particularly in settings of low LDL-C and high triglycerides 3

Clinical Implications

• The impact of fasting on LDL-C levels and measurement accuracy may have implications for clinical practice, including the use of non-fasting lipid assessments and the selection of LDL-C estimation methods 2, 3
• Further study is needed to fully understand the effects of fasting on LDL-C levels and measurement accuracy, and to inform clinical guidelines and practice 3