The use of chlorhexidine/n-propyl gallate as a urine preservative

Ambient-temperature storage of urine samples would increase the variety of life sciences studies that could be performed during spaceflight. The purpose of this study was to evaluate a preservative that would reduce the effects of oxidation and bacterial contamination on sample integrity and would be safe for personnel.

Chlorhexidine, a topical antiseptic, and n-propyl gallate, an antioxidant used in food production, were used in combination to produce a preservative (CPG) that meets these criteria. Urine pools were prepared and divided into three aliquots that were stored unpreserved at either -70 degrees C or room temperature (21 degrees C to 25 degrees C), or stored preserved with CPG at ambient temperature. Analyte measurements were conducted on days 1, 14, and 28, and monthly thereafter for one year. Stability was defined as the ability of a test condition to result in analyte values within the acceptable range established with the reference condition (-70 degrees C).

CPG effectively maintained stability of ammonia for 14 days, total nitrogen and 3-methylhistidine for three months, chloride for four months, sodium for five months, potassium for seven months, and urea for 12 months. Creatinine and osmolality were not preserved by CPG.

These data indicate that CPG offers prolonged room-temperature storage for multiple urine analytes, reducing the requirements for frozen urine storage on future spaceflights. In medical applications on Earth, this technology can allow urine samples to be collected in remote settings and eliminate the need to ship frozen samples.