Urine collection pads: are samples reliable for urine biochemistry and microscopy?

The aim of the study was to validate the reliability of samples obtained with urine collection pads (UCP) for selected laboratory biochemical analyses, urine cell microscopy, and bedside semi-quantitative stick urinalysis. A series of laboratory experiments was performed to test agreement between urine concentrations, or results, before and after passage through a UCP (incubated for 37 degrees C for 15 min). The following urinalyses were performed: electrolytes, calcium, phosphate, urate, osmolality, pH, protein, catecholamines, toxicology for drugs of abuse, stick urinalysis for glucose, ketones, protein, blood, leucocytes and nitrites, and microscopy for red and white cells. Close agreement was shown for all laboratory analyses except proteinuria, which was underestimated by, on average, 10% after UCP passage. However, stick urinalysis for proteinuria remains sufficiently reliable for clinical use. UCP substantially retain or destroy red and white cells, but stick urinalysis for blood and leucocyte esterase remains reliable. In conclusion, urine samples derived from UCP show good agreement across a clinically relevant range for the biochemical analyses undertaken in this study. Microscopy of UCP samples is unreliable for cellular material but semi-quantitative stick urinalysis for red and white cells is a satisfactory alternative.