According to our estimation, for a patient with dialysis time of approximately 4.1 years, the initial values of uNGAL (3�C6h after transplantation) are about 242ng/mL higher in patients who went on to develop DGF, and these values will rise even more in the following days. A significant interaction between time of measurement and DGF confirmed that longitudinal changes of uNGAL levels depend on whether the recipient had DGF or not. To clarify the meaning of this interaction, Figure 2 shows the predicted uNGAL trajectories over time for four hypothetical subjects: two recipients who developed DGF (one with 4years of dialysis and one with 10years), and two other patients with prompt graft function (similar time on dialysis, 4 and 10years). Hypothetically, the remaining variables were equal in all four patients. The predicted uNGAL values were estimated using the coefficients estimates of Table 3 (e.g., the predicted uNGAL values at the first day for a recipient with 4 years of dialysis with prompt function = exp [(5.46 ? 2.14) + 0.94 + 0.4 + (0.076 4 years of dialysis)] = 158ng/mL). Figure 2 Predicted uNGAL values over time of four hypothetical subjects, estimated from multiple linear mixed model presented in Table 3. Abbreviations: uNGAL: urinary neutrophil gelatinase associated lipocalin; DGF: delayed graft function; non-DGF: prompt graft … Table 3 Results of the final linear mixed model for dependent variable ln(uNGAL) (n = 171 observations derived from 40 patients). 3.3. Prediction of DGF by uNGAL Levels (ROC analysis) Receiver-operating characteristic (ROC) curves showed uNGAL on the first postoperative days were accurate in predicting DGF (Tables (Tables44 and and5).5). Table 4 displays the derived sensitivities, specificities, and predictive values for uNGAL at the cutoff concentrations that provided the maximum sum of sensitivity and specificity. Regarding the areas under the ROC curves (AUC), the ability of uNGAL to predict DGF was moderately accurate at baseline and first day, and highly accurate at second, fourth, and seventh days (Table 5, Figure 3). In the first two posttransplant days the diagnostic performance of uNGAL was better than of serum creatinine, and quite similar to that of cystatin C. The reduction in serum creatinine between first and second days resulted in AUC = 0.78 [0.64�C0.92] and was worse than uNGAL for DGF prediction. Figure 3 Receiver-operating characteristic curves for uNGAL, serum creatinine and changes in serum creatinine, and serum cystatin C measured at posttransplant days 1 and 2 for predicting delayed graft function. Abbreviations: uNGAL: urinary neutrophil gelatinase … Table 4 Sensitivity, specificity, and predictive values for DGF using specific uNGAL cut-off values. Table 5 Area under the receiver-operating characteristic curve at each time point for uNGAL, serum creatinine, and serum cystatin C for predicting DGF. 3.4.