Table 4.
Improvement in the discrimination of the clinical model for the prediction of postoperative in-hospital AKI by combining the 2 clinical models used for the study with peak postoperative biomarker levels following cardiac surgery (peak levels from 6 hours post–cardiopulmonary bypass to postoperative day 1): the IDI and NRI are reported
| IDI | IDI events (95% CI) | IDI non-events (95% CI) | Absolute IDI (95% CI) | P |
|---|---|---|---|---|
| Clinical model 1 + peak of postoperative 6 h–POD 1 biomarkers | ||||
| Serum cystatin C | 0.038 (−0.005 to 0.081) | 0.011 (−0.008 to 0.029) | 0.048 (0.002–0.095) | 0.042 |
| Urine NGAL/Cr | 0.016 (−0.010 to 0.042) | 0.004 (−0.006 to 0.015) | 0.021 (−0.008 to 0.049) | 0.15 |
| Urine KIM-1/Cr | 0.018 (−0.010 to 0.046) | 0.005 (−0.007 to 0.017) | 0.023 (−0.007 to 0.053) | 0.14 |
| Combination 1 Serum cystatin C + urine KIM-1/Cr | 0.040 (−0.004 to 0.085) | 0.011 (−0.010 to 0.032) | 0.051 (0.002–0.101) | 0.041 |
| Combination 2 Serum cystatin C + urine KIM-1/Cr | 0.030 (−0.010 to 0.069) | 0.008 (−0.008 to 0.024) | 0.038 (−0.005 to 0.081) | 0.081 |
| Clinical model 2 + peak of postoperative 6 h–POD 1 biomarkers | ||||
| Serum cystatin C | 0.070 (0.005–0.135) | 0.019 (−0.003 to 0.042) | 0.089 (0.021–0.158) | 0.011 |
| Urine NGAL/Cr | 0.017 (−0.007 to 0.040) | 0.013 (−0.007 to 0.033) | 0.004 (−0.008 to 0.016) | 0.16 |
| Urine KIM-1/Cr | 0.043 (−0.003 to 0.089) | 0.034 (−0.009 to 0.076) | 0.009 (−0.008 to 0.027) | 0.066 |
| Combination 1 Serum cystatin C + urine KIM-1/Cr | 0.059 (0.025–0.093) | 0.016 (−0.009 to 0.041) | 0.075 (0.033–0.117) | 0.001 |
| Combination 2 Serum cystatin C + urine KIM-1/Cr | 0.052 (−0.000 to 0.104) | 0.014 (−0.001 to 0.035) | 0.066 (0.010–0.122) | 0.021 |
| NRI | NRI (95% CI) | % of events correctly reclassified | % of no-events correctly reclassified | P |
| Clinical model 1 + peak of postoperative 6 h–POD 1 biomarkers | ||||
| Serum cystatin C | 0.56 (0.12–1.00) | 30.44 (−10.43 to 71.30) | 25.30 (3.79–46.82) | 0.018 |
| Urine NGAL/Cr | 0.41 (−0.05 to 0.86) | 13.04 (−27,83 to 53.91) | 27.71 (6.20–49.23) | 0.084 |
| Urine KIM-1/Cr | 0.41 (−0.05 to 0.86) | 13.04 (−27.83 to 53.91) | 27.71 (6.20–49.23) | 0.084 |
| Combination 1 Serum cystatin C + urine KIM-1/Cr | 0.73 (0.38–1.08) | 73.91 (33.04–1.15) | −1.20 (−22.72 to 20.31) | 0.002 |
| Combination 2 Serum cystatin C + urine KIM-1/Cr | 0.56 (0.12–0.99) | −13.04 (−53.91 to 27.83) | 68.68 (47.16–90.19) | 0.018 |
| Clinical model 2 + peak of postoperative 6 h–POD 1 biomarkers | ||||
| Serum cystatin C | 0.67 (0.24–1.10) | 39.13 (−1.74 to 80.00) | 27.71 (6.20–49.23) | 0.005 |
| Urine NGAL/Cr | 0.20 (−0.26 to 0.66) | 4.35 (−36.52 to 45.22) | 15.66 (−5.85 to 37.18) | 0.40 |
| Urine KIM-1/Cr | 0.27 (−0.19 to 0.73) | 4.35 (−36.52 to 45.22) | 22.89 (1.38–44.41) | 0.25 |
| Combination 1 Serum cystatin C + urine KIM-1/Cr | 0.66 (0.29–1.04) | 65.22 (24.35–1.06) | 1.20 (−2.03 to 22.72) | 0.005 |
| Combination 2 Serum cystatin C + urine KIM-1/Cr | 0.56 (0.12–0.99) | −13.04 (−53.91 to 68.68) | 68.68 (47.16–90.19) | 0.018 |
AKI, acute kidney injury; CI, confidence interval; Cr, creatinine; IDI, integrated discrimination improvement; KIM-1, kidney injury molecule 1; NGAL, neutrophil gelatinase-associated lipocalin; NRI, net reclassification improvement; POD, postoperative day.
Clinical model 1 consisted of 3 preoperative clinical parameters that either were significantly associated with AKI in univariate analysis (preoperative left ventricular ejection fraction percent and body mass index >30 kg/m2) or were clinically relevant for the model (preoperative estimated glomerular filtration rate <60 ml/min per 1.73 m2). Clinical model 2 was the Cleveland Clinic score validated for predicting AKI–renal replacement therapy following cardiac surgery.30 Duplets of biomarkers were combined as follows: (i) at least 1 biomarker above the cutoff value (combination 1), or (ii) both biomarkers above the cutoff value (combination 2). Biomarker data were log10 transformed.