Assessment of Dehydration in Older Adults

Diagnostic Approach

Serum osmolality is the gold standard for assessing dehydration, with a threshold of >300 mOsm/kg indicating dehydration in older adults 1, 2, 3
Directly measured serum osmolality >300 mOsm/kg should be used to identify low-intake dehydration in older adults 2, 3
When direct measurement is not available, calculated serum osmolarity using the equation: osmolarity = 1.86 (Na+ + K+) + 1.15 glucose + urea + 14 (all measured in mmol/L) with an action threshold of >295 mmol/L can be used as a screening tool 4, 5
Simple clinical signs and tests commonly used to assess dehydration should NOT be used as they lack diagnostic accuracy, particularly in older adults: skin turgor, mouth dryness, weight change 1
Bioelectrical impedance should NOT be used to assess hydration status in older adults as it has not been shown to be diagnostically useful 1, 3

All older persons should be considered at risk of low-intake dehydration 4
Assessment of fluid intake by care staff is often highly inaccurate, with studies showing poor correlation (r = 0.122) between staff-recorded and actual fluid intake 4
Older persons and their informal carers may use appropriate tools to assess fluid intake, but should also request serum osmolality assessment periodically 1, 4

In older adults, renal function is often poor, making renal parameters unreliable indicators of dehydration 2, 5
Clinical judgment alone is highly fallible in assessing dehydration in older adults 2, 5
Assessment of fluid intake by care staff is frequently inaccurate, often underestimating actual intake by approximately 700 ml/day 1, 4

For older adults with measured serum osmolality >300 mOsm/kg who appear unwell, subcutaneous or intravenous fluids should be offered in parallel with encouraging oral fluid intake 1, 3
In mild dehydration, older persons should be encouraged to drink more fluid according to preference (tea, coffee, fruit juice, water, etc.) 1, 3
Oral rehydration therapy and sports drinks are NOT indicated for low-intake dehydration 1, 3