Background: Although it is widely assumed that dehydration predisposes to venous thromboembolism (VTE), there are no clinical studies to support this.
Aim: To evaluate the relationship between biochemical indices of dehydration and VTE after acute ischaemic stroke (AIS).
Design: Prospective observational study.
Methods: Unselected AIS patients (n = 102) receiving standard thromboprophylaxis with aspirin and graded compression stockings, underwent serial measurements of serum urea, creatinine and osmolality, and were screened for VTE using magnetic resonance direct thrombus imaging.
Results: Serum osmolality of >297 mOsm/kg, urea >7.5 mmol/l and urea:creatinine ratio (mmol:mmol) >80 a few days post-AIS were associated with odds ratios for VTE of, respectively, 4.7, 2.8 and 3.4 (p = 0.02, 0.05, 0.02) on multivariable analysis.
Discussion: Dehydration after AIS is strongly independently associated with VTE, reinforcing the importance of maintaining adequate hydration in these patients.