Urine Tests Found To Have Low Accuracy for Screening Dehydration in Older Adults – June 24, 2016

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According to new research published in The American Journal of Clinical Nutrition, urine tests should not be used to screen for dehydration among the elderly because their diagnostic accuracy is too low to be useful.

 

Water-loss dehydration is common among elderly people and linked with associated risks of adverse health effects and death. Research has shown that older people who are dehydrated have 40% increased risk of mortality and double the risk of developing a new disability compared with older people who are well-hydrated. Dehydration is linked to longer stays in the hospital and higher mortality. Forty percent of older people admitted to UK hospitals and 16% of older adults living in residential care are dehydrated.

Water-loss dehydration occurs when insufficient fluid is consumed and is characterized by elevated serum osmolarity in blood. Not enough fluid is consumed to replace normal fluid losses through urine, breath, sweat, and breath, resulting in body fluids becoming more concentrated. In older people, the reference standard for water-loss dehydration is serum osmolality.

The early detection, prevention and treatment of dehydration would potentially enhance the health of older people and decrease healthcare costs. Even though serum osmolality in the blood is the reference standard in older people, it is too invasive for everyday monitoring outside of the hospital and expensive to monitor regularly. As a result, urine specific gravity (USG), urine colour and urine osmolality indicators, which can be obtained by urine tests and be analyzed with minimal training and cost, are commonly used by physicians, nurses and other health professionals to screen for water-loss dehydration among older people.

However, evidence supporting the use of urine tests in older adults has been weak, although their use seems to be useful in younger adults. Researchers aimed to investigate the diagnostic accuracy of urinary measures to screen for water-loss dehydration in older people by using serum osmolality as the reference standard. They assessed the data from elderly people 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. Both blood and urine samples were tested of 383 males and females aged 65 and older, all of whom were living in nursing homes, residential care, or in their own homes in Suffolk and Norfolk, UK. The urine samples were tested for cloudiness, pH, volume, specific gravity, osmolality, colour, and glucose. The researchers measured the serum osmolality of the participants’ blood to determine if they were drinking sufficient fluids to stay hydrated, and compared the findings with urine samples taken at the same time. Participants were classified as normally hydrated, having impending dehydration, or current dehydration.

The researchers showed, in the largest study to date, that 22% of NU-AGE participants and 19% of DRIE participants and were dehydrated. Significantly, urine tests had a very low diagnostic accuracy. Although USG was better than chance at indicating impending dehydration and current dehydration in both DRIE and NU-AGE participants, USG nor any of the other tests were specific or sensitive enough to be used as a diagnostic for water-loss dehydration. The urine tests identified many older adults as dehydrated when in reality they were not, and indicated that many adults were well hydrated when they were in fact dehydrated.

The colour of urine in older people is not associated with their fluid levels. First, urine can be coloured by foods such as blackberries and beetroot, or drugs such as warfarin used to thin the blood. Second, these urine tests rely on normal kidney function. Although urine tests do appear to be able to suggest dehydration in children and younger adults, aging is related to impaired kidney function. The ability of the body to concentrate urine declines with age, and so, urine tests are not useful in elderly adults for recognizing hydration. Therefore, urine colour, USG, urine volume, urine osmolality, and urinary measures such as, glucose, pH and protein are not sensitive or specific enough, and thus, should not be used to screen for dehydration in older people. The researchers suggest that inexpensive, simple, and non-invasive tools be developed for the assessment of dehydration in elderly people.

 

 

 

Written By: Nigar Celep, BASc