Concentration of kidney markers and detection of exosomes in urine samples collected in cotton wool balls in preterm and term neonates.

Collecting urine samples in neonates by catheterisation or suprapubic puncture causes trauma, whereas self-adhesive collection bags can damage fragile skin. An alternative method is the collection of samples from urine-soaked cotton wool balls placed in diapers. The aim of this study was to compare the concentration of albumin, creatinine, neutrophil gelatinase-associated lipocalin (NGAL), and uromodulin between clean-catch urine and samples collected in cotton wool balls in neonates and assess the efficiency of exosome extraction. Standard clean-catch urine samples were assayed for albumin, creatinine, NGAL, and uromodulin using commercial enzyme-linked immunosorbent assay (ELISA) kits. Concentrations were compared to the same urine samples extracted immediately from soaked cotton wool balls (sample 2, S2) or the urine extracted from cotton wool balls placed in a diaper in a warm incubator for 2 h before extraction (sample 3, S3). Exosomes were extracted from all three samples of one patient for visualisation by electron microscopy. Twenty-six infants (17 males) of median gestational age at birth of 32+1 weeks had urine collected at a median age of 29 days at 37+6 weeks corrected age. Concentrations in S2 and S3 were within 10% of the concentration of standard samples in 46% and 35% of specimens for albumin, 69% and 58% for creatinine, 12% and 12% for NGAL, and 27% and 15% for uromodulin, respectively, without consistent positive or negative bias. Urine albumin/creatinine ratios (UACRs) were 4.3% less in S2 and 4.5% less in S3 than in standard samples. Exosomes were extracted and visualised from all three sample types. Neonatal urine samples extracted from cotton wool balls can be used to screen for relevant albuminuria ​but provide imprecise estimates of NGAL and uromodulin. The proof of exosome extraction from urine collection in cotton wool balls opens the potential to examine exosomal cargo.