Malnutrition in elderly patients with pulmonary tuberculosis: a systematic review and meta-analysis of prevalence, comparison of prevalence estimates by diagnostic tool, and evidence gaps

Background Elderly patients with pulmonary tuberculosis are at high risk for malnutrition, yet prevalence estimates vary widely, risk-factor evidence is fragmented, and “nutritional risk” is often conflated with malnutrition. We aimed to estimate the prevalence of strictly defined malnutrition in this population, compare estimates across malnutrition definitions, and evaluate the evidence base for risk factors. Methods We searched PubMed, Embase, Web of Science, Cochrane Library, CINAHL, China National Knowledge Infrastructure, and Wanfang from inception to September 2026 for studies reporting malnutrition prevalence or determinants in patients aged ≥60 years. Eligible studies used (1) the complete GLIM framework, (2) a GLIM-compatible low-BMI phenotype (BMI < 18.5 kg/m2 alone), or (3) MNA-based tools (MNA < 17 or MNA-SF ≤ 7). Quality was assessed with design-specific JBI checklists. Prevalence was pooled using a random-effects generalized linear mixed model (binomial likelihood, logit link); sensitivity analyses used an inverse-variance model with Hartung-Knapp-Sidik-Jonkman adjustment. Results Fifteen studies (5,346 patients) were included. The overall pooled prevalence was 38.8% (95% CI: 30.5–47.9%), with substantial heterogeneity (I2 = 96.4%). In the prespecified comparison, GLIM-based definitions yielded 39.2% (95% CI: 31.3–47.7%) and MNA-based tools 37.9% (95% CI: 14.7–68.5%; p = 0.936). In the exploratory three-tier decomposition, the single full-GLIM study reported 47.6% (95% CI: 45.0–50.2%), GLIM-compatible low-BMI studies (k = 11) 38.4% (95% CI: 30.0–47.6%), and MNA-based tools (k = 3) 37.9% (95% CI: 14.7–68.5%). Hospital-based studies showed higher prevalence than community-based cohorts (44.6% vs. 21.7%, p < 0.001; only two community studies). The 95% prediction interval was 13.2–72.6%. Excluding four TB-diabetes studies did not materially change the estimate (39.8%, 95% CI: 28.6–52.2%). Few studies performed multivariable adjustment; diabetes, drug-resistant tuberculosis, and frailty were potential risk factors, but most could not be pooled because definitions were inconsistent. Conclusion Strictly defined malnutrition affects over one-third of elderly tuberculosis patients. Clinical setting was the main source of heterogeneity, and the available evidence was insufficient to draw conclusions about the comparability of different diagnostic definitions. Confusion between nutritional risk and malnutrition further limits the evidence base. Future multicenter prospective studies using the complete GLIM workflow with standardized, age-appropriate criteria are needed. Systematic review registration PROSPERO; Identifier CRD420261357409.