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%
	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*
	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:

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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