Patterns of Quetelet Index (Body Mass Index) Improvement and Associated Clinical Factors During Initial Tuberculosis Treatment: A Prospective Analysis of Newly Diagnosed Tuberculosis Patients

Abstract

Introduction Tuberculosis (TB) and malnutrition form a detrimental synergistic relationship, with malnutrition weakening the immune system and increasing susceptibility to TB, while TB, in turn, worsens the nutritional status through increased metabolic demands and decreased appetite. The nutritional recovery is expected during treatment, but the extent and rate of improvement may vary based on patient characteristics, disease severity, and presence of comorbidities. This study aimed to assess the nutritional status changes in newly diagnosed TB patients by evaluating and comparing their body mass index (BMI) at treatment initiation and after the completion of intensive phase (two months) while also analysing the influence of various factors (age, gender, bacterial load, drug sensitivity, and comorbidities) on BMI variations during this period. Methods A prospective longitudinal study was conducted among 116 newly diagnosed pulmonary TB patients at a tertiary medical college hospital in Tamil Nadu between August and October 2021. Baseline assessments included demographic data, sputum microscopy for bacterial load, drug sensitivity testing via the Cartridge-Based Nucleic Acid Amplification Test (CBNAAT)/TrueNat, and screening for diabetes mellitus and chronic kidney disease (CKD). Anthropometric measurements (weight and BMI) were recorded at treatment initiation and after the completion of a two-month intensive phase treatment using standardized protocols. Data analysis was performed using IBM SPSS Statistics for Windows, V. 23.0 (IBM Corp., Armonk, NY, USA), with descriptive statistics for demographic and clinical characteristics, comparative analyses using independent t-test and one-way ANOVA for subgroup BMI improvements, and McNemar's test and paired t-test for assessing changes in BMI from baseline to post-two-month treatment (p < 0.05 considered significant). Results Among 116 pulmonary TB patients, mean (SD) BMI significantly increased from 16.17 (4.15) to 16.96 (4.01) kg/m² during the intensive phase treatment (p < 0.001). Of 89 initially malnourished patients, 9% achieved normal BMI status. Younger patients (<30 years) showed higher BMI improvement (1.12 ± 0.51 kg/m²) compared to the elderly (>70 years: 0.56 ± 0.49 kg/m²). Lower BMI improvements were observed in rifampicin-resistant cases (0.48 ± 0.22 vs 0.80 ± 0.50 kg/m²) and patients with comorbidities (diabetes: 0.74 ± 0.53 vs 0.85 ± 0.46 kg/m²; CKD: 0.65 ± 0.51 vs 0.83 ± 0.49 kg/m²), though these differences were not statistically significant. Conclusion Significant improvements in nutritional status were observed during the intensive phase treatment, with younger age associated with better BMI gains. Though not statistically significant, drug resistance and the presence of comorbidities appeared to negatively influence nutritional recovery, suggesting the need for enhanced nutritional monitoring and support in these vulnerable subgroups.

Keywords: anthropometry; body mass index; newly diagnosed tuberculosis; quetelet index; tuberculosis.