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Rapid TB Diagnosis Using GeneXpert and GeneXpert Ultra

  • April 01,2022
  • 1 Min Read
Rapid 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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