Urine diagnostics in paediatric intestinal failure: A prospective cohort study of alternative sampling methods

Regular monitoring of urinary electrolyte excretion and kidney function is essential in children with intestinal failure (IF) receiving long-term parenteral nutrition (PN). This study evaluated alternative urine sampling methods against 24-h urine collection (UC) and assessed the prevalence of chronic kidney disease (CKD) and renal abnormalities.

In this prospective single-centre cohort study, 31 paediatric IF patients underwent 24-h UC, spot urine (SU) sampling, and shorter timed collections at predefined intervals. Urinary electrolytes and derived ratios were analysed. Kidney function was evaluated using cystatin C (CysC)- and creatinine (Cr)-based estimated glomerular filtration rate (eGFR) and 24-h urinary Cr clearance (CrCl). Agreement between alternative sampling methods and 24-h UC was assessed using Bland-Altman and regression analyses. Renal abnormalities were evaluated by ultrasound.

Shorter timed UCs, particularly those corresponding to the PN infusion interval, showed the closest agreement with 24-h UC for sodium, magnesium, calcium, and phosphate excretion. Certain SU samples detected electrolyte deficiencies, particularly sodium and magnesium depletion, and low sodium-to-potassium ratios, highlighting cyclic dehydration at the end of the PN-free interval. CKD was detected in 15/30 patients (50%) by creatinine-cysC-based eGFR. Proteinuria was present in 17/29 patients (58.6%) in 24-h UC, and albuminuria in 13/26 SU samples (50%). Nephrocalcinosis was found in 37% of patients.

Shorter timed UC and targeted SU samples may provide practical alternatives to 24-h UC for monitoring urinary electrolyte status and hydration. CKD and renal abnormalities are prevalent in children with IF receiving PN.