Comparative Prognostic Performance of Platelet-Containing and Platelet-Free Inflammatory Indices After Percutaneous Coronary Intervention

Background/Objectives: Systemic inflammatory indices derived from the complete blood count differ in whether they incorporate platelet count. Whether platelet-containing indices outperform platelet-free indices and whether platelet count adds independent prognostic information remain insufficiently tested. Methods: We retrospectively analyzed 2244 consecutive patients undergoing percutaneous coronary intervention (PCI) at a single center. The neutrophil-to-lymphocyte ratio (NLR), systemic inflammatory response index (SIRI), systemic immune–inflammation index (SII) and pan-immune–inflammation value (PIV) were derived from the baseline blood count. The outcome was 1-year (400-day) major adverse cardiovascular events (MACEs). Because SII and PIV equal NLR and SIRI multiplied by platelet count, the platelet contribution was tested with nested likelihood ratio tests. Calibration, decision-curve, 30-day landmark, time-varying coefficient and subgroup analyses were also performed. Results: MACEs occurred in 170 patients (7.6%). After adjustment, NLR, SII and PIV remained associated with MACEs. SII showed the highest C-index and lowest AIC, but no index significantly improved discrimination over the clinical model (ΔC-index +0.009, p = 0.060 for SII), no head-to-head difference was detected, and the added net benefit was negligible (0.38 per 100 patients). Adding platelet count did not improve model fit over the whole follow-up (p = 0.104 and 0.146) but did beyond the 30-day landmark (p = 0.025 and 0.033); the platelet-by-period interaction was not significant (p = 0.197). Exploratory analyses suggested larger associations in ST-segment elevation MI based on few events. Only the adjusted SII association survived within-family Holm correction; no result met the global 5% false-discovery-rate threshold. Conclusions: The four indices showed similar, modest discrimination without evidence of superiority or meaningful incremental utility; the post-30-day platelet signal was not confirmed by interaction testing and remains hypothesis-generating.