Back-calculating baseline creatinine overestimates prevalence of acute kidney injury with poor sensitivity.

AIM: Acute kidney injury (AKI) is diagnosed by a 50% increase in creatinine. For patients without a baseline creatinine measurement, guidelines suggest estimating baseline creatinine by back-calculation. The aim of this study was to evaluate different glomerular filtration rate (GFR) equations and different GFR assumptions for back-calculating baseline creatinine as well as the effect on the diagnosis of AKI. METHODS: The Modification of Diet in Renal Disease, the Chronic Kidney Disease Epidemiology (CKD-EPI) and the Mayo quadratic (MQ) equation were evaluated to estimate baseline creatinine, each under the assumption of either a fixed GFR of 75 mL min-1  1.73 m-2 or an age-adjusted GFR. Estimated baseline creatinine, diagnoses and severity stages of AKI based on estimated baseline creatinine were compared to measured baseline creatinine and corresponding diagnoses and severity stages of AKI. RESULTS: The data of 34 690 surgical patients were analysed. Estimating baseline creatinine overestimated baseline creatinine. Diagnosing AKI based on estimated baseline creatinine had only substantial agreement with AKI diagnoses based on measured baseline creatinine [Cohen's κ ranging from 0.66 (95% CI 0.65-0.68) to 0.77 (95% CI 0.76-0.79)] and overestimated AKI prevalence with fair sensitivity [ranging from 74.3% (95% CI 72.3-76.2) to 90.1% (95% CI 88.6-92.1)]. Staging AKI severity based on estimated baseline creatinine had moderate agreement with AKI severity based on measured baseline creatinine [Cohen's κ ranging from 0.43 (95% CI 0.42-0.44) to 0.53 (95% CI 0.51-0.55)]. CONCLUSION: Diagnosing AKI and staging AKI severity on the basis of estimated baseline creatinine in surgical patients is not feasible. Patients at risk for post-operative AKI should have a pre-operative creatinine measurement to adequately assess post-operative AKI.

Impact of preoperative serum creatinine on short- and long-term mortality after cardiac surgery: a cohort study.

BACKGROUND: Preoperative renal insufficiency is an important predictor of mortality after cardiac surgery. This retrospective cohort study was designed to identify the optimal cut-off for baseline serum creatinine (bSCr) and estimated glomerular filtration rate (eGFR) to predict survival. Furthermore, we investigated the potential confounding effect of other perioperative risk indicators on short- and long-term survival. METHODS: Data of 9490 cardiac surgical patients were prospectively collected between 1997 and 2008 (follow up to 2010) at the Medical University Vienna. We identified bSCr cut-off values and calculated uni- and multivariate hazard models for short- and long-term survival and compared the results with a validation set from Zurich. The estimated survival curves defined a distinct period of increased mortality until 150 days. RESULTS: Cut-off values of >115 µmol litre(-1) for bSCr and ≤50 ml min(-1) for eGFR were identified. Increased bSCr, associated with higher mortality [hazard ratio (HR) 2.61, 95% confidence interval (CI) 2.43-2.80, P<0.0001], was present in 19.5% of patients and remained predictive for short- (HR 1.59, 95% CI 1.38-1.83, P=0.0027) and long-term survival (HR 1.46, 95% CI 1.32-1.62, P<0.0001) in the multivariate hazard models. A cut-off of >120 µmol litre(-1) for bSCr was determined for the validation set. Decreased eGFR was present in 23.6% (HR 2.86, 95% CI 2.67-3.06, P<0.0001). CONCLUSIONS: In our patients, increased bSCr was an independent predictor of mortality, which may critically influence risk evaluation and perioperative treatment guidance.