Detecting dehydration in older people: useful tests

Dehydration is common in older people, leading to longer hospital stays and increased disability and mortality. We can diagnose dehydration by taking a blood sample and measuring serum osmolality, but it would be useful to be able to tell when older people are dehydrated (not drinking enough) using a less invasive test. Tests, signs and questions are commonly used to screen for dehydration, and include dry mouth and tongue, skin turgor, axillary dryness, urinary tests, pulse rate, questions and routine blood test results. But, their usefulness in screening for dehydration in older people has been questioned.

Evidence suggests limited evidence that any individual test, clinical sign or question tested to date is useful in screening for dehydration in older people. Some tests may have some diagnostic utility, including expressing fatigue, missing some drinks between meals, bioelectrical impedance analysis (BIA) at 50kHz, and salivary osmolality. Use of laboratory reports to provide opportunistic information on hydration status when older people have blood tests for other reasons may also be feasible. But all these tests, signs and questions need assessing again or in larger studies to determine how useful they really are.

There is some evidence that tests often used to assess dehydration in older people should not be used, but this evidence comes from small numbers of very small studies. These include urine colour, urine specific gravity, urine volume, heart rate, dry mouth, and feeling thirsty.

Risk factors for dehydration and poor fluid intake in older people include increasing age, being female, obesity and presence of comorbidities, dementia, functional limitations, incontinence and diuretic use.

At present there are no clearly useful simple tests, signs or questions to help nurses to screen for dehydration in older people, but there are some promising tests which need further assessment.