Background: Several inflammatory scores such as the Systemic Inflammation Response Index (SIRI), the Inflammation Index Score (IIS), and the Neutrophil Lymphocyte Ratio (NLR) have been reported to have prognostic value in PDAC with different results. We hypothesize that the KS, designed to predict the risk of cancer-associated thrombosis, may also be a surrogate marker for inflammation to be included as a relevant prognostic index for PDAC. Methods: Baseline characteristics and individual SIRI, IIS, NLR and KS indexes from 197 PDAC patients diagnosed in our center between 2019 and 2021 have been retrospectively recorded. PFS and OS (Log-rank test) have been used to compare the different scores of each index in the whole population as well as in the metastatic setting. Kruskal-Wallis test and Mann-Whitney test were also done to determine if the SIRI varies significantly between KRS values. Results: Of the 197 patients analyzed, 41 were resectable (20.8%), 54 locally advanced (27.4%) and 102 metastatic (51.8%). Patients with intermediate risk according to KS (2 points, n = 131, 66.5%) had a significantly higher median PFS (8.4 vs. 4.8 months, p = 0.03) and significantly higher OS (12.9 vs. 7.7 months, p = 0.002) than those with high-risk (> 3 points, n = 66, 33.5%). The median OS for patients with low (< 3,000) and high (> 3,000) SIRI was 13.1 and 9.3 months respectively (p = 0.05). No significant differences were observed in PFS. In the metastatic setting, a low SIRI was significantly associated with higher OS (10.6 vs. 5.8, p = 0.016). No significant differences were observed in patients with low vs. high IIS and NLR. The Kruskal-Wallis test indicates that SIRI values vary between at least two KS values (p < 0.001). The Mann-Whitney test found significant differences between the SIRI values from S 2 and 3 (p = 0.002) as well as 2 and 4 (p = 0.04). SIRI values were higher in patients with KRS > 3 vs. 2. Conclusions: This retrospective analysis showed that patients with lower KS live longer and progress later than those with higher KS. Lower SIRI is associated with better survival in metastatic patients, being on the verge of statistical significance in the whole cohort. There is a strong correlation between SIRI and KS. In this cohort of unselected PDAC patients, KS is a prognostic factor for OS and PFS that correlates with subclinical inflammation and demonstrates to be a better predictor than other inflammatory indexes that deserves further analysis.