Acute kidney injury calculated using admission serum creatinine underestimates 30-day and 1-year mortality after acute stroke

Background. Acute kidney injury (AKI) diagnosis requires ascertainment of change from a known baseline. Although preadmission serum creatinine (SCr) is recommended, to date, all studies of AKI in acute stroke have used the first SCr on admission. Methods. All patients admitted with an acute stroke to an emergency hospital were recruited. We compared use of preadmission SCr with admission SCr to diagnose AKI. Regression analyses were used to identify risk factors for 30-day and 1-year mortality, respectively. Results. A total of 1354 patients were recruited from December 2012 to September 2015. Incidence of AKI was 18.7 and 19.9% using pre-admission SCr and admission SCr, respectively. Diagnosis of AKI was associated with significantly increased 30-day and 1-year mortality. Diagnosis of AKI using pre-admission SCr had a stronger relationship with both 30-day and 1-year mortality. In 443 patients with a pre-admission SCr and at least two SCr during admission, AKI diagnosed using pre-admission SCr had a stronger relationship than AKI diagnosed using admission SCr with 30-day mortality [odds ratio (OR) = 2.64; 95% confidence interval (CI) 1.36-5.12; P = 0.004 versus OR = 2.10; 95% CI 1.09-4.03; P = 0.026] and 1-year mortality [hazard ratio (HR) = 1.90, 95% CI 1.32-2.76; P = 0.001 versus HR = 1.47; 95% CI 1.01-2.15; P = 0.046] in fully adjusted models. Conclusions. AKI after stroke is common and is associated with increased 30-day and 1-year mortality. Using first SCr on admission gives a comparable AKI incidence to pre-admission SCr, but underestimates 30-day and 1-year mortality risk.