Diagnostic Accuracy of Prognostic Nutritional Index and Systemic Immune–Inflammatory Index in Predicting Fibrosis and Histological Activity in Chronic Hepatitis B

Background: Liver biopsy remains the gold standard for staging chronic hepatitis B (CHB), yet it is invasive, costly, and associated with potential complications. There is a critical need for non-invasive, cost-effective biomarkers to monitor disease progression. This study aimed to evaluate the correlation between the Prognostic Nutritional Index (PNI) and Systemic Immune–Inflammatory Index (SII) with histological fibrosis stages and the Histological Activity Index (HAI) in patients with CHB. Methods: This retrospective study analyzed 274 patients diagnosed with CHB (HBsAg positivity > 6 months) who underwent liver biopsy at the University of Health Sciences, Kanuni Sultan Süleyman Training and Research Hospital between February 2016 and February 2022. Histopathological findings were staged using the Ishak fibrosis score and HAI. PNI and SII were calculated from peripheral blood parameters. Statistical discrimination power was assessed using Area Under the Receiver Operating Characteristic (AUROC) curves. Results: The cohort comprised 119 females (43.4%) and 155 males (56.6%), with a mean age of 45.25 ± 11.2 years. Mean values were 55.83 ± 5.33 for PNI and 494.37 ± 336.86 for SII. Fibrosis distribution showed 56.2% at stages F0–F1 and 43.8% at ≥F2. For fibrosis staging, SII demonstrated statistically significant but limited predictive ability for Ishak scores ≥F2, while PNI was significant for identifying advanced fibrosis (≥F4) (p < 0.05). SII showed moderate diagnostic performance for severe inflammation (HAI ≥12; AUROC = 0.848), although this finding should be interpreted cautiously. For lower HAI thresholds (≥6), both PNI and SII demonstrated poor discriminative ability (AUROC 0.5–0.6). Conclusions: Both indices were associated with histological parameters but showed limited overall diagnostic performance. SII appeared relatively better; however, this was descriptively observed without formal statistical comparison. These markers may provide complementary information but should not be used as standalone diagnostic tools.