Background: Bioelectrical impedance analysis (BIA) is a commonly used noninvasive technique for body composition assessment with recently expanded indications. This reproducible measurement method uses electrical conductivity to evaluate body composition, including fluid status. In pediatric idiopathic nephrotic syndrome (INS), albumin leaks into the urine, resulting in dysregulated colloid-osmotic pressure in the blood vessels. This results in decreased circulating blood volume and edema. Blood tests are a useful evaluation method; however, it cannot be performed frequently in children because of their invasive nature. Herein, we present a case of a child with INS demonstrating a longitudinal correlation between serum albumin (S-Alb) levels and extracellular water (ECW)/total body water (TBW) ratio.

Case description: A 6-year-old boy was admitted to the hospital for INS treatment after informed consent was obtained. He presented with severe proteinuria symptoms and an increased weight of 3 kg before the onset of INS. Standard treatment with prednisolone (PSL) for 28 days was initiated, and his proteinuria resolved on day 7. During the acute course, albumin replacement was conducted thrice for fluid management purposes and did not cause severe intravascular dehydration. The fluid composition was assessed over time; each measurement lasted for approximately 10 minutes and was performed on the same day as the blood tests. Nine measurements were taken, and S-Alb levels and the ECW/TBW ratio (r=-0.72, P<0.04) exhibited a significant negative correlation.

Conclusions: BIA can potentially predict S-Alb levels objectively and noninvasively within a short period. Although further validation is needed, this measurement can reduce the invasiveness of testing in children with INS.