Suburban

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
  • Ideal sample: Sputum
  • Alternative samples (only in those who cannot produce sputum):
    • Nasopharyngeal aspirate
    • Gastric aspirate
GeneXpert

MTB/RIF

or

GeneXpert Ultra MTB/RIF

Signs and symptoms of EPTB
  • CSF
  • Lymph node aspirate
  • Lymph node biopsy
  • Pleural fluid
  • Peritoneal fluid
  • Pericardial fluid
  • Synovial fluid
  • Urine

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

  1. 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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