Urine Biomarkers and Perioperative Acute Kidney Injury: The Impact of Preoperative Estimated GFR.

BACKGROUND: The interaction between baseline kidney function and the performance of biomarkers of acute kidney injury (AKI) on the development of AKI is unclear.

STUDY DESIGN: Post hoc analysis of prospective cohort study.

SETTING & PARTICIPANTS: The 1,219 TRIBE-AKI Consortium adult cardiac surgery cohort participants.

PREDICTOR: Unadjusted postoperative urinary biomarkers of AKI measured within 6 hours of surgery.

OUTCOME: AKI was defined as AKI Network stage 1 (any AKI) or higher, as well as a doubling of serum creatinine level from the preoperative value or the need for post-operative dialysis (severe AKI).

MEASUREMENTS: Stratified analyses by preoperative estimated glomerular filtration rate (eGFR) ≤ 60 versus > 60mL/min/1.73m(2).

RESULTS: 180 (42%) patients with preoperative eGFRs≤60mL/min/1.73m(2) developed clinical AKI compared with 246 (31%) of those with eGFRs>60mL/min/1.73m(2) (P<0.001). For log2-transformed biomarker concentrations, there was a significant interaction between any AKI and baseline eGFR for interleukin 18 (P=0.007) and borderline significance for liver-type fatty acid binding protein (P=0.06). For all biomarkers, the adjusted relative risk (RR) point estimates for the risk for any AKI were higher in those with elevated baseline eGFRs compared with those with eGFRs≤60mL/min/1.73m(2). However, the difference in magnitude of these risks was low (adjusted RRs were 1.04 [95% CI, 0.99-1.09] and 1.11 [95% CI, 1.07-1.15] for those with preoperative eGFRs≤60mL/min/1.73m(2) and those with higher eGFRs, respectively). Although no biomarker displayed an interaction for baseline eGFR and severe AKI, log2-transformed interleukin 18 and kidney injury molecule 1 had significant adjusted RRs for severe AKI in those with and without baseline eGFRs≤60mL/min/1.73m(2).

LIMITATIONS: Limited numbers of patients with severe AKI and post-operative dialysis.

CONCLUSIONS: The association between early postoperative AKI urinary biomarkers and AKI is modified by preoperative eGFR. The degree of this modification and its impact on the biomarker-AKI association is small across biomarkers. Our findings suggest that distinct biomarker cutoffs for those with and without a preoperative eGFR≤60mL/min/1.73m(2) is not necessary.