TB Diagnosis Using GeneXpert and GeneXpert Ultra
Initial diagnostic tests with sample type as recommended by the WHO:(1)
| Adults/Children | Disease | Recommended Samples | Recommended Test(s) |
| Adults/Children
(with or without a history of TB) |
Signs and symptoms of PTB/chest radiograph with lung abnormalities |
|
GeneXpert
MTB/RIF or GeneXpert Ultra MTB/RIF |
| Signs and symptoms of EPTB |
|
PTB – Pulmonary TB; EPTB – Extrapulmonary TB
GeneXpert and GeneXpert Ultra are the recommended tests for Rapid TB Diagnosis.(1)
In case of a negative result on GeneXpert Ultra, broth-based culture can be done if there still exists a strong clinical suspicion of TB. (1)
Performance of GeneXpert & GeneXpert Ultra MTB/RIF (according to the WHO):(1)
| Adults/Children | Disease | Sample | GeneXpert
MTB/RIF Sensitivity |
GeneXpert Ultra
MTB/RIF Sensitivity |
|
| Adults | PTB | Sputum | 85% | 90% | |
| PTB – Smear Negative | Sputum | 67% | 77% | ||
| PTB – HIV +ve | Sputum | 81% | 88% | ||
| EPTB | CSF | 70% | 87% | ||
| EPTB | Lymph node aspirate | 89% | 78% | ||
| EPTB | Lymph node biopsy | 82% | 90% – 100% | ||
| EPTB | Pleural fluid | 50% | 71% | ||
| EPTB | Peritoneal fluid | 59% | Not Available* | ||
| EPTB | Pericardial fluid | 66% | Not Available* | ||
| EPTB | Synovial fluid | 97% | 96% | ||
| EPTB | Urine | 85% | 100% | ||
| Children | PTB | Sputum | 65% | 73% | |
| PTB | Gastric aspirate# | 73% | Not Available* | ||
| PTB | Nasopharyngeal aspirate | 46% | 46% | ||
| PTB – Smear Negative | Sputum | 59% | Not Available* | ||
| PTB – HIV +ve | Sputum | 72% | Not Available* | ||
| PTB – HIV +ve | Gastric aspirate# | 73% | Not Available* | ||
| EPTB | CSF | 54% | Not Available* | ||
* – Sensitivity not published by the WHO
# – Gastric aspiration is not used for adults; it can be useful in children who cannot produce sputum.
GeneXpert MTB/RIF Ultra is the new, next generation GeneXpert test for TB:
- Improved performance
- 10-fold improvement in the lower limit of TB detection
- Higher sensitivity, especially in smear negative cases
- Increased accuracy of rifampicin resistance results
REFERENCES
- World Health Organization. WHO consolidated guidelines on tuberculosis: module 3: diagnosis: rapid diagnostics for tuberculosis detection [Internet]. 2021 update. Geneva: World Health Organization; 2021 [cited 2022 Mar 16]. Available from: https://apps.who.int/iris/handle/10665/342331
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