Performance of the Abbott RealTime MTB RIF/INH resistance assay when used to test MTB specimens from Bangladesh

Figures & data

Table 1 Percentage of samples with RT MTB RIF/INH results greater than assay LOD

Microscopy status	RT MTB RIF/INH resistance results		RT MTB RIF/INH below LOD results
	NALC/ NaOH pellets	Sputum	NALC/ NaOH pellets	Sputum
Positive	98.2 (110/112)	96.4 (108/112)	1.8 (2/112)	3.6 (4/112)
Negative	85.0 (17/20)	85.0 (17/20)	15.0 (3/20)	15.0 (3/20)
Total	96.2 (127/132)	94.7 (125/132)	3.8 (5/132)	5.3 (7/132)

Abbreviations: RT MTB RIF/INH, RealTime MTB RIF/INH Resistance Assay; MTB, Mycobacterium tuberculosis; RIF, rifampicin; INH, isoniazid; LOD, limit of detection.

Table 2 RIF assay results of Hain, Xpert, and RT MTB RIF/INH compared against DST

Assay results	DST
Hain	Resistant	Sensitive
RIF resistant	27	1
RIF sensitive	5	89
Hain RIF sensitivity =84.4% (27/32) [95% CI 67.2%-94.7%]
Hain RIF specificity =98.9% (89/90) [95% CI 94.0%-100.0%]
Hain RIF PPV =96.4% (27/28) [95% CI 81.7%-99.9%]
Hain RIF NPV =94.7% (89/94) [95% CI 88.0%-98.3%]
Xpert
RIF resistant	28	0
RIF sensitive	4	90
Xpert RIF sensitivity =87.5% (28/32) [95% CI 71.0%-96.5%]
Xpert RIF specificity =100% (90/90) [95% CI 96.0%-100.0%]
Xpert RIF PPV =100.0% (28/28) [95% CI 87.7%-100.0%]
Xpert RIF NPV =95.7% (90/94) [95% CI 89.5%-98.8%]
RT MTB RIF/INH
RIF resistant	28	0
RIF sensitive	4	90
RT MTB RIF/INH RIF sensitivity =87.5% (28/32) [95% CI 71.0%-96.5%]
RT MTB RIF/INH RIF specificity =100% (90/90) [95% CI 96.0%-100.0%]
RT MTB RIF/INH RIF PPV =100.0% (28/28) [95% CI 87.7%-100.0%]
RT MTB RIF/INH RIF NPV =95.7% (90/94) [95% CI 89.5%-98.8%]

Abbreviations: RT MTB RIF/INH, RealTime MTB RIF/INH Resistance Assay; MTB, Mycobacterium tuberculosis; RIF, rifampicin; INH, isoniazid; DST, drug sensitivity testing; PPV, positive predictive value; NPV, negative predictive value.

Table 3 Comparison of RT MTB RIF/INH and Xpert RIF probe responses

		Number of samples with Xpert RIF probe responses
		A	B	C	D	E
Number of samples	1
with RT MTB RIF/	2		1
INH probe responses	3
	4					19
	5	3	3
	6
	7				2
	8

Abbreviations: RT MTB RIF/INH, RealTime MTB RIF/INH Resistance Assay; MTB, Mycobacterium tuberculosis; RIF, rifampicin; INH, isoniazid.

Table 4 INH assay results of Hain and RT MTB RIF/INH compared against DST

Assay results	DST
Hain	Resistant	Sensitive
INH resistant	26	0
INH sensitive	6	90
Hain INH sensitivity =81.3% (26/32) [95% CI 63.6%-92.8%]
Hain INH specificity =100% (90/90) [95% CI 96.0%-100.0%]
Hain INH PPV =100.0% (26/26) [95% CI 86.8%-100.0%]
Hain INH NPV =93.8% (90/96) [95% CI 86.9%-97.7%]
RT MTB RIF/INH	Resistant	Sensitive
INH resistant	28	5
INH sensitive	4	85
RT MTB RIF/INH INH sensitivity =87.5% (28/32) [95% CI 71.0%-96.5%]
RT MTB RIF/INH INH specificity =94.4% (85/90) [95% CI 87.5%-98.2%]
RT MTB RIF/INH INH PPV =84.8% (28/33) [95% CI 68.1%-94.9%]
RT MTB RIF/INH INH NPV =95.5% (85/89) [95% CI 88.9%-98.8%]

Abbreviations: RT MTB RIF/INH, RealTime MTB RIF/INH Resistance Assay; MTB, Mycobacterium tuberculosis; RIF, rifampicin; INH, isoniazid; DST, drug sensitivity testing; PPV, positive predictive value; NPV, negative predictive value.