Clinical utility of urinary liver-type fatty acid binding protein measured by latex-enhanced turbidimetric immunoassay in chronic kidney disease

Background:Urinary liver-type fatty acid binding protein (L-FABP) measured by enzyme-linked immunosorbent assay method (ELISA) was approved as a clinical biomarker of tubular damage by the Japanese Ministry of Health, Labor and Welfare (MHLW) in 2011. We evaluated a new latex-enhanced immunoturbidimetric assay (LTIA) to evaluate the clinical utility of urinary L-FABP measured by LTIA versus an ELISA assay.Methods:LTIA with anti-human L-FABP mouse monoclonal antibodies was performed using an automated clinical chemistry analyzer. Five positive samples with low, medium and high L-FABP concentrations were analyzed to determine the within-run precision. In patients with chronic kidney disease (CKD) (n=91), urinary L-FABP levels were measured by ELISA and LTIA.Results:Measurement of urinary L-FABP revealed urinary L-FABP levels within 30 min. The within-run coefficient of variation was 10.0% for 1.4 ng/mL, 4.4% for 2.5 ng/mL, 3.2% for 9.8 ng/mL, 1.5% for 50.1 ng/mL, and 1.2% for 102.7 ng/mL. Concentrations of urinary L-FABP measured by LTIA were significantly correlated with those measured by ELISA (ρ=0.932). Proportional systematic error was almost within limits of agreement (LOA). Urinary L-FABP levels measured by LTIA were significantly correlated with urinary albumin (ρ=0.634), urinary NAG (ρ=0.688) and eGFR (ρ=–0.561).Conclusions:Measurement of urinary L-FABP by LITA was simple, speedy, and similar in quality to ELISA results. Therefore, this method was approved as external body diagnosing medicines by the Japanese MHLW in 2014. Urinary L-FABP is expected to be widely used in various pathophysiological conditions by measuring urinary L-FABP using LTIA.