Clinical and analytical evaluation of an immunoturbidimetric heart-type fatty acid-binding protein assay

Heart-type fatty acid-binding protein (H-FABP) is a low molecular weight protein involved in the intracellular uptake and buffering of long chain fatty acids in the myocardium. It is an early marker for ACS. We have evaluated the Randox Laboratories immunoturbidimetric assay on a Siemens Advia 1800 analyzer. The assay employs latex particles coated with mouse monoclonal anti-HFABP antibodies to generate turbidity.

We used redundant patient samples and pools to assess precision, functional sensitivity, limit of detection, linearity, recovery of recombinant H-FABP and interference. We evaluated the 99th centile values and compared H-FABP with troponin in samples routinely received from chest pain patient samples.

Precision was typically < 10% and 12.5% at all concentrations for within and between batches. The functional sensitivity was 2.4 μg/L. The assay was linear on dilution over the range 2.76-115 μg/L. Recovery of recombinant H-FABP was approximately 20-25%. No interference was seen with haemoglobin concentrations <1.5 g/L, bilirubin < 250 μg/L and triacylglycerol < 5 mmol/L or rheumatoid factor. The 99th centile value in a reference population with eGFR > 60mL/min/1.73m(2) was 9.1 μg/L with no significant gender difference. H-FABP was measured in routine clinical samples (N = 1310) received for troponin I measurement. Using Siemens TnI > 50 ng/L as an indicator of myocardial damage, the ROC area under curve for H-FABP was 0.82.

The immunoturbidimetric H-FABP assay is robustly designed and shows good analytical performance. It is therefore well suited for use in a routine clinical laboratory.