Association of the CALLY index with malnutrition risk in patients with nasopharyngeal carcinoma: a cross-sectional study

Background Malnutrition is a prevalent complication in nasopharyngeal carcinoma (NPC) patients, yet simple screening tools are lacking. The CALLY index, integrating CRP, albumin, and lymphocytes, has not been evaluated in this population. We aimed to investigate the association between the CALLY index and malnutrition in NPC patients. Methods This cross-sectional study enrolled 148 NPC patients at the First Affiliated Hospital of Xiamen University between June and December 2025. Malnutrition was defined as PG-SGA ≥ 4. Multivariable logistic regression, restricted cubic spline, and two-piecewise regression models were used to evaluate the association. Bootstrap internal validation (2,000 resamples) was performed to assess the stability of the identified threshold. Results Malnutrition prevalence was 44.6% (66/148). After multivariable adjustment, each 1-unit increase in CALLY index was associated with a 18% lower odds of malnutrition (OR = 0.82, 95% CI: 0.73–0.92, p = 0.001), with a significant dose–response trend ( p < 0.001). A non-linear relationship with a threshold at 3.147 was identified: below this value, the OR was 0.215 (95% CI: 0.086–0.538, p = 0.001); above it, the association was not statistically significant (OR = 1.01, 95% CI: 0.65–1.57, p = 0.970). Sensitivity analyses excluding BMI or prior therapy yielded results consistent with the primary analysis in direction, but categorical estimates were unstable due to sparse events and should be interpreted with caution (adjusted OR = 0.81, 95% CI: 0.71–0.93, p = 0.003; adjusted OR = 0.44, 95% CI: 0.24–0.82, p = 0.009, respectively). Bootstrap validation showed that the median inflection point was 3.130, and 91.9% of resamples identified a threshold within ±0.5 of 3.147. Conclusion The CALLY index is independently and inversely associated with malnutrition in NPC patients, with a potential exploratory threshold at 3.147. This threshold requires external validation before clinical application. The CALLY index may serve as a potential biomarker for nutritional risk stratification, but further studies are needed.