Background: Accurate and rapid diagnosis of drug-resistant tuberculosis is essential for initiating appropriate treatment and preventing the transmission of these strains. This study compares phenotypic and genotypic methods of drug susceptibility testing for Mycobacterium tuberculosis (M. tuberculosis). Methods: Resistance to first-line drugs, as well as resistance to second-line drugs (fluoroquinolones and aminoglycosides), was assessed using the Löwenstein–Jensen medium phenotypic method and the GenoType MTBDRplus genotypic method and analyzed. Results: The phenotypic resistance rate was 84.85% for INH (n = 56), 46.97% for RIF (n = 31), 48.48% for STR (n = 32), and 30.30% for EMB (n = 20). Of the MDR-TB isolates (n = 29), 41.37% were resistant to fluoroquinolones (n = 12) and 31.03% were resistant to both fluoroquinolones and injectable aminoglycosides, being classified as XDR-TB (n = 9). In addition, 22.73% of the MDR-TB isolates were resistant to all four first-line drugs (n = 15). The overall concordance between the line probe assay method and phenotypic testing was 94.74% for RIF and 95.16% for INH. Discordances were identified in three cases for RIF and two cases for INH, where isolates were reported as susceptible by GenoType MTBDRplus, but phenotypically resistant. Conclusions: Genotypic testing using GenoType MTBDRplus provides rapid and accurate results, but some cases of phenotypic resistance are not detected by this method. The results highlight the importance of using combined phenotypic and genotypic methods for accurate diagnosis of MDR-TB, as well as the need to integrate genomic sequencing to improve diagnostic accuracy.

Background/Objectives: The rapid diagnosis of tuberculous pleural effusion (TPE) presents significant challenges for clinicians due to its paucibacillary nature. Routine biochemical markers may complement microbiological and molecular tests, especially in resource-limited settings. The objective of this study was to evaluate the diagnostic performance of pleural fluid adenosine deaminase (ADA), lactate dehydrogenase (LDH), total protein (TP), and the ADA/LDH and ADA/TP ratios for tuberculous pleural effusion, using Löwenstein–Jensen culture and Xpert MTB/RIF as microbiological reference standards Methods: We conducted a retrospective study (2016–2024) including 325 consecutive patients investigated for suspected TPE in a tertiary hospital. ADA, TP and LDH were measured, and additional ratio-based indices (ADA/TP, ADA/LDH) were calculated for 325 pleural fluid (PF) samples. Löwenstein–Jensen (LJ) culture (with MPT64 confirmation) and GeneXpert MTB/RIF (Xpert MTB/RIF) were used as separate microbiological reference standards. Sensitivity (Se), specificity (Sp), and areas under the ROC curve (AUC) were estimated, and optimal thresholds were determined using the Youden index. Results: Among 325 pleural fluid samples, 23 (7.1%) were culture-positive. Xpert MTB/RIF was performed in 73/325 patients (22.5%), with Mycobacterium tuberculosis detected in 19/73 (26.0%) tested samples. In PF, ADA provided the best performance against culture, with Se of 100%. Correlation analysis in PF showed a moderate positive association between TP and LDH (p < 0.0001). Conclusions: Among routine biochemical markers, PF ADA shows high NPV. Integrating these rapid, low-cost tests alongside LJ culture and Xpert MTB/RIF may streamline the diagnostic pathway for TPE.