Urea and Minerals Monitoring in Space Missions by Spot Samples of Saliva and Urine.

BACKGROUND: Microgravity induces redistribution of body fluids and reductions in muscle and bone mass. These effects correlate with changes in lab test results, including urea and bone minerals. Difficulties with collecting blood and urine during space missions limit the available data. This pilot study investigated metabolic changes during a space mission using untimed spot samples of urine and saliva. Untimed spot urine was used for urinalysis with data normalization per creatinine concentration. Saliva was proven useful as an index of serum urea and phosphorus.METHODS: Two astronauts collected urine and saliva samples 75 ± 5 d before launch (baseline) and 3-5 times during a 6-mo space mission. Samples were collected 3 h after morning breakfast. Urine was collected using a standard NASA device. Saliva was collected using a Salivette™ synthetic swab. Samples were kept frozen using automated biochemistry until lab work-up. Anthropometric data were collected at baseline and after the mission.RESULTS: For astronauts 1 and 2, respectively, total bone mineral density decreased (-1.4% and -0.9%). In-flight changes were as follows: transiently decreased urine urea/creatinine ratio (-32% and -24%), transiently decreased urine phosphorus/creatinine ratio (-52% and -30%), increased urine calcium/creatinine ratio (up to +116% and +27%), and transient increases in saliva urea (up to +48% and +195%) and phosphorus (up to +29% and +46%). The astronaut with greater changes in urine minerals had greater reduction in bone mineral density.DISCUSSION: The results support the hypothesis that untimed samples of urine and saliva are useful for investigation of metabolic changes during space missions. Changes in urine and saliva minerals suggested down-regulation of parathyroid gland activity during the space mission