Diagnostic Value of Complete Blood Count-Derived Inflammatory Indices for Predicting Adverse Outcomes in Geriatric Patients Presenting to the Emergency Department with Acute Infectious Diarrhea in the MIMIC-IV Database

Background Acute infectious diarrhea remains a leading cause of morbidity and mortality worldwide. Similar to pediatric populations, geriatric patients represent a highly vulnerable group with increased hospitalization rates, prolonged length of stay, heightened dehydration susceptibility, diminished physiological reserve, and elevated mortality risk. While pediatric populations benefit from well-established clinical severity scores such as Vesikari and Clark scales, analogous prognostic tools specifically validated for geriatric patients with acute gastroenteritis remain lacking. Specific inflammatory markers such as procalcitonin and C-reactive protein require additional testing and increase costs. Complete blood count (CBC)-derived inflammatory indices offer a practical alternative as they are inexpensive, universally available, and calculated from routine tests. Methods This retrospective study utilized the MIMIC-IV database (2008–2019) to assess diagnostic accuracy of nine CBC-derived inflammatory indices (AISI, NPAR, HALP, NLR, SII, PLR, MLR, SIRI, PNI) for predicting adverse outcomes in geriatric patients (≥ 65 years) with acute infectious diarrhea. Patients were identified using ICD-9 codes (008–009 infectious diarrhea, 003–005 bacterial/foodborne; n = 2,208) and ICD-10 codes (A02-A05 bacterial/foodborne, A08 viral enteritis, A09 infectious gastroenteritis unspecified; n = 1,868), yielding 3,934 patients. Exclusions (n = 1,087) comprised non-infectious gastroenteritis, inflammatory bowel disease, radiation enteritis, ischemic colitis, drug-induced diarrhea, immunosuppressed patients, missing laboratory data, and C. difficile recurrence. Results Among 2,847 immunocompetent geriatric patients, comorbidities included hypertension (32.8%), diabetes mellitus (18.6%), and chronic kidney disease (10.4%). Bacterial pathogens were identified in 276 (9.7%) and viral in 151 (5.3%; norovirus 64.1%, rotavirus 23.4%, adenovirus 12.5%). Hospital admission occurred in 668 (23.5%), ICU in 34 (1.2%), mortality in 14 (0.5%), and AKI in 421 (14.8%). Bacterial infections demonstrated significantly elevated indices versus viral: AISI (9,845 vs 920, 10.7-fold), NLR (14.8 vs 1.82, 8.1-fold; all p < 0.001). For bacterial-viral differentiation, NLR achieved AUC 0.892. In bacterial infections (n = 276), AISI demonstrated highest accuracy for AKI (AUC 0.896), ICU (0.882), and mortality (0.868); NPAR showed comparable results (AKI 0.854, ICU 0.872, mortality 0.848). In viral infections (n = 151), indices showed moderate performance: AISI for AKI (AUC 0.782), ICU (0.768), mortality (0.754); NPAR for AKI (0.764), ICU (0.756), mortality (0.742). HALP achieved strong mortality prediction in both groups (bacterial 0.874, viral 0.768). In diabetic patients (n = 530), AISI achieved exceptional accuracy (AUC 0.908 for AKI) with higher complications (AKI 26.8% vs 12.1%; p < 0.001). CKD patients (n = 296) showed highest complications (AKI 38.6%, mortality 2.1%). Multivariable analysis confirmed AISI (aOR 1.052), NPAR (aOR 1.046), and HALP (aOR 0.91) as independent predictors (all p < 0.001). Conclusions Among nine CBC-derived indices evaluated in geriatric patients with acute infectious diarrhea, AISI, NPAR, and HALP demonstrate superior diagnostic value for predicting AKI, ICU admission, and mortality, with higher accuracy in bacterial compared to viral infections. These cost-effective biomarkers may address the current gap in geriatric-specific prognostic tools.