Objective Severe acute kidney injury (AKI) after cardiac surgery is significantly associated with increased adverse clinical outcomes. The prognostic utility of current biomarkers is just moderate. We conducted a prospective study to evaluate whether miR-21 can serve as a novel biomarker for postoperative AKI progression.
Methods We measured urine and plasma miR-21 by quantitative real-time PCR in 120 adult patients undergoing cardiac surgery, including 40 non-AKI control, 39 patients with progressed AKI and 41 with non-progressed AKI. The association of miR-21 level with progression of AKI was determined by proper statistical methods.
Results Both urine and blood miR-21 level were up-regulated in patients with AKI and significantly associated with the progression of AKI. The level of urine and plasma miR-21 identified established AKI by AUC 0.68 (95% CI 0.59–0.78) and 0.80 (95% CI 0.73–0.88), respectively. Using multiple logistic regression analysis, we determined the risk of AKI progression. After adjustment for clinical model, the prognostic predictive power of urinary and plasmatic miR-21 increased to AUC 0.81 (95% CI 0.72–0.91) and 0.83 (95%CI 0.74–0.92), respectively. Both urine and plasma miR-21 demonstrated remarkable predictive capability for postoperative need for renal replacement therapy (RRT) with AUC 0.99 (95% CI 0.96 – 1.00, P = 0.003) and 0.97 (95% CI 0.90 –1.00, P = 0.005), 30 day in-hospital mortality and prolonged stay in hospital or ICU after surgery. Compared to plasma miR-21, urine miR-21 performed as a better predictor for associating with a 2.6-fold (95% CI 1.4 – 4.9), 1.7-fold (95% CI 1.3 – 2.3) and 1.6-fold (95% CI 1.3 – 2.0) unadjusted odds for RRT, in-hospital death and development of AKIN stage 3 AKI, respectively.
Conclusions Urinary and plasmatic miR-21 are significantly associated with severe AKI and other poor outcomes of postoperative patients and may be used as promising predictive factors in the field of cardiac surgery.