Apolipoprotein A and B Testing Does Not Require Fasting
Apolipoprotein (apo) A and apolipoprotein (apo) B testing does not require fasting conditions, as the assay performs well without fasting and is not sensitive to moderately high triglyceride levels. 1
Technical Advantages of Apolipoprotein Testing
- From a technical standpoint, there are significant advantages in measuring apo B and apo A-I compared to traditional lipid measurements 1
- Good immunochemical methods are available that can be easily run on conventional autoanalyzers with good analytical performance 1
- The apolipoprotein assay does not require fasting conditions and is not sensitive to moderately high triglyceride levels 1
- Unlike LDL-C calculations that can be affected by non-fasting state, apolipoprotein measurements remain reliable regardless of fasting status 1
Clinical Significance of Apolipoproteins
- Apo B is the major apolipoprotein of atherogenic lipoprotein families (VLDL, IDL, and LDL) and provides a good estimate of the number of these particles in plasma 1, 2
- Apo A-I is the major protein component of HDL and provides a good estimate of HDL concentration 1
- The apo B/apo A-I ratio represents the balance between atherogenic and anti-atherogenic particles and is considered a marker of cardiovascular risk 3
- Elevated levels of apo B and reduced levels of apo A-I are associated with increased cardiac events 2
Comparison with Traditional Lipid Testing
- While traditional lipid panels (LDL-C, HDL-C) typically require fasting samples for accurate measurement, especially with elevated triglycerides, apolipoproteins can be reliably measured in non-fasting samples 1
- Under certain circumstances, particularly in patients with hypertriglyceridemia, the measurement of apo B may have advantages over traditional lipid measurements 1
- The apo B/apo A-I ratio has been shown in large prospective studies to be a strong indicator of cardiovascular risk 1, 3
Practical Considerations
- Unlike the Friedewald formula for calculating LDL-C (which becomes unreliable with non-fasting samples or triglycerides ≥4.5 mmol/L or >400 mg/dL), apolipoprotein measurements remain accurate in non-fasting states 1
- Research has demonstrated that apolipoprotein levels correlate well with their respective lipoprotein fractions regardless of fasting status 4, 5
- The ability to measure apolipoproteins without fasting improves patient convenience and compliance with testing 1
Caveats and Limitations
- Despite the technical advantages of apolipoprotein measurements, most risk estimation systems and drug trials are still based on traditional lipid measurements (TC and LDL-C) 1
- Apolipoprotein B measurement carries extra expense compared to standard lipid panels, and its measurement in some laboratories may not be reliable 1
- While non-fasting apolipoprotein measurements are accurate, fasting lipid profiles may still be reasonable for initial evaluation in adults with a family history of premature ASCVD or genetic hyperlipidemia 1