Some methodological issues in studying the long-term renal sequelae of acute kidney injury
Division of Nephrology, University of California, San Francisco, San Francisco, California 94143-0532, USA.Current opinion in nephrology and hypertension (Impact Factor: 3.96). 04/2009; 18(3):241-5. DOI: 10.1097/MNH.0b013e328329d0a3
There has been great interest recently in better understanding how an episode of acute kidney injury (AKI) affects risk of development or acceleration of chronic kidney disease. This area of epidemiology research presents several methodological challenges that have not been sufficiently discussed in the literature. These are related to the current consensus definitions of AKI; the determination of 'baseline' renal function before the AKI episode; and the possibility that observed associations between AKI and future adverse events are confounded by differences in the severity of baseline chronic kidney disease. In this study, we discuss several potential solutions to these problems. Concerted efforts to address these methodological issues will propel research in this field to a higher level.
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ABSTRACT: To determine whether acute renal failure (ARF) increases the long-term risk of progressive chronic kidney disease (CKD), we studied the outcome of patients whose initial kidney function was normal or near normal but who had an episode of dialysis-requiring ARF and did not develop end-stage renal disease within 30 days following hospital discharge. The study encompassed 556,090 adult members of Kaiser Permanente of Northern California hospitalized over an 8 year period, who had pre-admission estimated glomerular filtration rates (eGFR) equivalent to or greater than 45 ml/min/1.73 m(2) and who survived hospitalization. After controlling for potential confounders such as baseline level of eGFR and diabetes status, dialysis-requiring ARF was independently associated with a 28-fold increase in the risk of developing stage 4 or 5 CKD and more than a twofold increased risk of death. Our study shows that in a large, community-based cohort of patients with pre-existing normal or near normal kidney function, an episode of dialysis-requiring ARF was a strong independent risk factor for a long-term risk of progressive CKD and mortality.
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ABSTRACT: Studies of acute kidney injury usually lack data on pre-admission kidney function and often substitute an inpatient or imputed serum creatinine as an estimate for baseline renal function. In this study, we compared the potential error introduced by using surrogates such as (1) an estimated glomerular filtration rate of 75 ml/min per 1.73 m(2) (suggested by the Acute Dialysis Quality Initiative), (2) a minimum inpatient serum creatinine value, and (3) the first admission serum creatinine value, with values computed using pre-admission renal function. The study covered a 12-month period and included a cohort of 4863 adults admitted to the Vanderbilt University Hospital. Use of both imputed and minimum baseline serum creatinine values significantly inflated the incidence of acute kidney injury by about half, producing low specificities of 77-80%. In contrast, use of the admission serum creatinine value as baseline significantly underestimated the incidence by about a third, yielding a low sensitivity of 39%. Application of any surrogate marker led to frequent misclassification of patient deaths after acute kidney injury and differences in both in-hospital and 60-day mortality rates. Our study found that commonly used surrogates for baseline serum creatinine result in bi-directional misclassification of the incidence and prognosis of acute kidney injury in a hospital setting.
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