What is H-FABP?
Fatty acid-binding proteins (FABPs) are small cytoplasmic proteins that are abundantly expressed in tissues with an active fatty acid metabolism, such as the heart and liver (Viswanathan et al 2012), with their primary function being the facilitation of intracellular long-chain fatty acid transport. Nine distinct types of the FABP family have been identified, with Heart-type FABP (H-FABP) being the most widely studied, largely due to the fact that it is found in abundance in the cardiomyocytes.
The combination of their low molecular weight and cytoplasmic location means that H-FABP proteins are released very rapidly following Acute Myocardial Infarction (AMI).
|Biomarker||Molecular Weight (kDa)||Initial Elevation in blood||Time to peak||Return to normal||Comments|
|H-FABP||15kDa||30 mins||6-12 hrs||24 hrs||Early rise specificity|
|Myoglobin||17kDa||1-3 hrs||5-8 hrs||16-24 hrs||Early rise Low specificity|
|Troponin I (TnI)||22kDa||3-6 hrs||14-18 hrs||5-10 days||Late rise High specificity|
|Troponin T (TnT)||33kDa||3-6 hrs||10-48 hrs||10-15 days||Late rise High specificity|
|CK-MB||86kDa||3-8 hrs||9-24 hrs||48-72 hrs||Late rise High specificity|
Furthermore, H-FABP has been repeatedly shown to be a highly sensitive early rise biomarker across the full spectrum of acute coronary syndrome (ACS), detectable as early as 30 minutes following the onset of an ischemic episode.
H-FABP concentrations typically peak at approximately 6-8 hours after symptom onset and return to normal within 24-30 hours. Although H-FABP has similar release kinetics to Myoglobin (i.e. rapid release & clearance), it is approximately 15-20 times more cardiac specific, hence making it a vastly more efficacious biomarker for myocardial injury. Furthermore, the normal serum/plasma value of H-FABP is much lower than with Myoglobin, which reduces the potential for false positive results.
H-FABP: Release Kinetics
A secondary benefit of the H-FABP release kinetics after AMI is that since it returns to baseline concentrations so rapidly (i.e. typically 20-24 hours), it can be used as a biomarker for reinfarction in the days following an initial AMI. This has been a common utility of CK-MB historically, due to its more rapid clearance than with Troponin (3-4 days vs 10-14 days), but H-FABP offers potential use from as early as the second day onwards.
H-FABP in Reinfarction
H-FABP is a very stable protein in-vitro, as studies have shown that serum and plasma samples can be subjected to up to 8 freeze/thaw cycles without the loss of immunoreactivity.Diagnostic Value in Acute Coronary Syndrome