Urinary liver‐type fatty acid‐binding protein in pediatric nephrotic syndrome and tubular dysfunction

Background Urinary liver‐type fatty acid‐binding protein (uL‐FABP) has recently been identified as a biomarker for kidney injury. uL‐FABP excretion in pediatric relapsing nephrotic syndrome and tubular dysfunction, however, has not been reported previously. Methods We measured uL‐FABP level in children with steroid‐sensitive nephrotic syndrome (SSNS), in those with tubular dysfunction, and in control subjects. Results uL‐FABP was markedly increased in relapsing SSNS (median, 30.3 μg/gCr; range, 12.6–171.0 μg/gCr; n = 13), and also in the tubular dysfunction group (median, 164.8 μg/gCr; range, 41.6–834.5 μg/gCr; n = 7), compared with the control subjects (median, 3.0 μg/gCr; range, 1.1–13.9 μg/gCr; n = 21). uL‐FABP level was significantly correlated with urinary protein excretion in the SSNS group, and in the total group. Additionally, in the SSNS group, elevated uL‐FABP in the relapsing stage returned to a level similar to that in the control group on remission of NS. In the tubular dysfunction group, uL‐FABP was significantly correlated with urinary β2‐microglobulin. Conclusion Urinary protein amount, and the ability of the proximal tubules to reabsorb low‐molecular‐weight proteins, should also be considered when evaluating the clinical significance of uL‐FABP as a biomarker for kidney injury in children.