Use of cotton balls in diapers for collection of urine samples impacts the analysis of routine chemistry tests: an evaluation of cotton balls, diapers, and chemistry analyzers.

To evaluate the suitability of urine samples collected with cotton balls placed into diapers for routine laboratory chemistry analyses.
Twenty pools of residual unpreserved urine samples were separated into control and treated aliquots. The treated samples were absorbed into two different brands of cotton balls, wrapped in three different brands of diapers, and incubated at 37°C for one hour. The urine-soaked cotton balls were placed into a syringe and expressed via plunger depression. Urine sodium, potassium, creatinine, urea, calcium, magnesium, inorganic phosphorus, albumin, and total protein were measured on all samples on five automated clinical chemistry platforms: Ortho Vitros 4600, Siemens Dimension Vista 500, Beckman Coulter AU5822, Roche Cobas 6000, and Abbott Architect c8000 at five separate hospital laboratories. Criteria used to exclude the presence of significant effects of urine from pre-soaked cotton balls in a diaper on the measurement of chemistry laboratory tests were R >0.95, slope 0.9 – 1.1, and bias within ±10%.
Albumin and total protein measurements demonstrated significant negative bias in urine from both brands of pre-soaked cotton balls with all brands of diapers on all five chemistry platforms compared with the control urine. We did not observe a significant effect of pre-soaking urine in cotton balls in a diaper on the measurement of sodium, inorganic phosphorus, and urea. The remaining tests demonstrated significant effects when measured in urine from pre-soaked cotton balls and/or diapers that were specific to the chemistry analyzer platform or diaper.
Diaper and cotton ball-based urine collection significantly impacts the measurement of several common chemistry assays.

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