Older adults are susceptible to dehydration due to age-related changes. This study aimed to investigate the prevalence of clinically diagnosed dehydration in older adult medical emergency hospital admissions and assess the impact on length of hospital stay (LOS) and mortality.

Data were retrieved from the hospital's electronic database relating to all emergency admissions of patients aged≥65years between 1 April 2011 and 31 October 2013. The Charlson comorbidity index, LOS and mortality were calculated.

Of the 42,553 patients identified, 32,980 (77.5%) were admitted to medical specialties. Dehydration was noted in 2,932 (8.9%) patients and was the primary cause of admission in 190 (0.6%). The prevalence of dehydration also increased with age and comorbidity. Acute kidney injury was reported in 47.7% of patients with dehydration, compared with 15.9% of patients without dehydration, P<0.001. The median (interquartile range) LOS in patients diagnosed with dehydration was 8 (4–19) days compared with 3 (1–8) days in those without dehydration, P<0.001. Patients admitted with a primary diagnosis of dehydration had a 17% 30-day mortality and 44% one-year mortality compared with 7% and 25% respectively in patients without dehydration, P<0.001. Patients diagnosed with dehydration during hospitalisation were twice more likely to die in hospital, HR 2.11 (95% CI 1.92–2.32), P<0.001, independent of age, gender and comorbidities.

A small but significant proportion of hospitalised older adults was diagnosed with dehydration, which was associated with an increase in LOS and mortality, independent of age, gender and comorbidities.