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Urine Tests Not Accurate for Water-loss Dehydration in Elderly

October 3rd, 2016

NORWICH, UK – In emergency departments and elsewhere, urine tests are widely employed to help determine dehydration in older patients. The problem, according to a new British study? They aren’t always very accurate.

The report was published recently in the American Journal of Clinical Nutrition.

“Although USG, urine color, and urinary osmolality have been widely advocated for screening for dehydration in older adults, we show, in the largest study to date to our knowledge, that their diagnostic accuracy is too low to be useful, and these measures should not be used to indicate hydration status in older people (either alone or as part of a wider tranche of tests),” assert study authors, led by researchers from the University of East Anglia.

Background information in the article points out that water-loss dehydration — hypertonic, hyperosmotic, or intracellular dehydration — is caused by insufficient fluid intake and is different from hypovolemia due to excess fluid losses.

Adding that water-loss dehydration is associated with poor health outcomes such as disability and mortality in older patients, study authors explain that urine specific gravity (USG), urine color, and urine osmolality have been widely advocated for screening for dehydration in older adults.

"Around 20% of older people living in residential care don't drink enough fluid, so are dehydrated. This figure rises to around 40% among older adults admitted to hospital,” added lead researcher Lee Hooper, PhD, RD. "Dehydration often goes unnoticed by carers, but it can lead to increased risk of hospital admission, urinary tract infections, disability and even death.”

For the study, researchers assessed 383 men and women aged 65 years or older living in residential care, nursing homes, or in their own homes in Norfolk and Suffolk. They measured serum osmolality to assess whether the patients were drinking enough to stay hydrated — and compared the results with urine samples taken at the same time, testing for color, cloudiness, specific gravity, osmolality, volume, glucose, and pH.

Reviewed for the study were participants in the DRIE (Dehydration Recognition In our Elders; living in long-term care) or NU-AGE (Dietary Strategies for Healthy Aging in Europe; living in the community) studies. While 19% of DRIE participants and 22% of NU-AGE participants were dehydrated with serum osmolality greater than 300 mOsm/kg, neither the USG, nor any other potential urinary tests, were found to be accurately diagnostic for water-loss dehydration.

"Assessing a urine sample is simple and cheap. But our research shows that urine tests for dehydration are not fit for purpose — either alone or as part of a wider tranche of tests,” Hooper emphasized. “They are not sensitive or specific enough. Urine tests will indicate that some people are dehydrated when they are not, but the urine tests also miss some older adults who really are dehydrated.”

The study notes that urine color can be altered by medical conditions, drugs such as warfarin, and by eating certain foods such as beetroot or blackberries. Hooper added that urinary tests “rely on normal kidney function. While urine tests do seem to be able to indicate hydration status in children and younger adults, aging is associated with impaired kidney function. As we get older we cannot concentrate our urine as well as younger people — so urine tests are not useful in older adults for indicating hydration.”

"There is a great need to develop simple, inexpensive and noninvasive tools for the assessment of dehydration in older people,” study authors conclude.