From the Guidelines
The sensitivity of sputum TB GeneXpert (Xpert MTB/RIF) is approximately 89% for detecting pulmonary tuberculosis, as estimated by a systematic review 1. This estimate is based on the test's ability to detect the DNA of Mycobacterium tuberculosis through a real-time PCR method, providing results within 2 hours. The sensitivity of the Xpert MTB/RIF test can vary depending on the patient's smear status, with higher sensitivity in smear-positive, culture-positive TB cases (approximately 98%) and lower sensitivity in smear-negative, culture-positive cases (about 67-80%) 1. Some key points to consider when interpreting the sensitivity of the Xpert MTB/RIF test include:
- The test's sensitivity is affected by the bacterial load in the sample, with higher sensitivity in samples with higher bacterial loads 1.
- Proper sample collection technique is crucial to ensure accurate results, as poor technique can lead to false-negative results 1.
- Patient HIV status can also impact the test's sensitivity, with lower sensitivity in HIV-positive individuals 1.
- Multiple samples may be needed to increase diagnostic yield in patients with paucibacillary disease 1. Despite these limitations, the Xpert MTB/RIF test remains a valuable tool for detecting pulmonary tuberculosis, particularly in resource-limited settings where conventional smear microscopy and culture methods may not be available or feasible 1.
From the Research
Sensitivity of Sputum TB GeneXpert
- The sensitivity of sputum TB GeneXpert varies across different studies, with reported values ranging from 74.3% to 96.3% 2, 3.
- A study published in 2017 found that the sensitivity of GeneXpert MTB/RIF assay was 78.6% in smear-positive cases and 90.9% in smear-negative cases 4.
- Another study published in 2022 reported a sensitivity of 96.3% for GeneXpert in diagnosing smear-negative pulmonary tuberculosis 2.
- The sensitivity of GeneXpert MTB/RIF assay was also found to be 74.3% in smear-negative sputum samples, with a specificity of 96.6% 3.
- A comparison of GeneXpert MTB/RIF assay with conventional AFB smear for diagnosis of pulmonary tuberculosis found that the sensitivity of GeneXpert was 94% (95% CI: 84-98) 5.
Factors Affecting Sensitivity
- The sensitivity of GeneXpert may be affected by factors such as the presence of underlying diseases, HIV status, and the quality of the sputum sample 6, 5.
- A study found that the sensitivity of salivary Xpert Ultra was 24% lower among persons living with HIV than among persons living without HIV 6.
- The sensitivity of GeneXpert may also be affected by the type of sample used, with sputum samples generally considered to be more sensitive than saliva samples 6.