Urine tests should not be used to indicate hydration status in older people because their diagnostic accuracy “is too low to be useful,” researchers based in the UK and Ireland report.

“One in every five older adults in residential care, and two of every five older adults acutely admitted to hospital, are dehydrated because they drink too little,” Dr. Lee Hooper of Norwich Medical School, University of East Anglia, UK, told Reuters Health by email.

“Dehydration due to insufficient fluid intake is distinct from hypovolemia, which is due to excess fluid losses and associated with poor health outcomes such as disability and mortality in older people,” he explains.

“We can tell whether older adults are drinking enough, and remaining hydrated, by checking their blood (because) serum osmolality rises when we drink too little. But it is invasive and expensive to monitor serum osmolality regularly, so we use other methods (such as) urine specific gravity (USG), urine color, and urine osmolality to screen for dehydration,” he says.

To investigate the diagnostic accuracy of such measures, Dr. Hooper and colleagues analyzed data from individuals 65 and older taking part in the DRIE (Dehydration Recognition In our Elders; living in long-term care) or NU-AGE (Dietary Strategies for Healthy Ageing in Europe; living in the community) studies.

The team classified hydration status based on serum osmolality. Participants were categorized as normally hydrated (serum osmolality 275 to less than 295 mOsm/kg); having impending dehydration (295-300 mOsm/kg); or current dehydration (greater than 300 mOsm/kg). Seven participants with serum osmolality less than 275 mOsm/kg were included in the analysis as adequately hydrated, although they may have been over-hydrated.

A total of 162 DRIE participants provided a urine sample, as did 151 of NU-AGE participants. Urine measures included USG, color, cloudiness, volume, other dipstick tests such as glucose, ketones, blood, pH, protein, nitrite, leucocytes, and reasons for lack of a sample.

The researchers found that 19% of DRIE participants and 22% of NU-AGE participants were dehydrated, according to their May 25 online paper in the American Journal of Clinical Nutrition.

“Neither USG nor any other potential urinary tests were usefully diagnostic for water-loss dehydration,” they concluded.

According to Dr. Hooper, “When we used urinary tests, they identified many people as being dehydrated when this was not the case, and they suggested that many people were well hydrated when, in fact, they were dehydrated. Urine color was no better than chance at identifying whether an older person was dehydrated. USG was a tiny bit better than chance, but not nearly good enough to be useful.”