Aim: To assess weather doctors’ clinical risk-assessment for major adverse kidney events (MAKE) and acute kidney injury (AKI) after open-heart surgery would improve when being informed about neutrophil gelatinase-associated lipocalin (NGAL) test result at ICU admission. Patients & Methods: Clinical risk-assessment for MAKE and AKI were performed with and without providing NGAL test result and compared in an exploratory- and a validation-cohort using reclassification metrics, exemplary category-free net reclassification improvement (cfNRI). Results: Exploratory cohort: doctors’ prediction of MAKE (cfNRI = 0.750 [0.130–1.370]; p = 0.018) and AKI (cfNRI = 0.565 [0.001–1.129]; p = 0.049) improved being provided with NGAL test information. This finding was confirmed in the validation-cohort (MAKE cfNRI = 0.930 [0.188–1.672]; p = 0.014) and the combined-cohort (MAKE: cfNRI = 0.847 [0.371–1.323], p < 0.001); AKI: cfNRI = 0.468 [0.099–0.836; p = 0.013]). Improvements mostly generated from correctly reclassifying patients who not developed events (p < 0.001). Conclusion: Biomarker informed risk-assessment is superior in predicting MAKE and AKI after open-heart surgery.