Diagnostic role of Xpert-MTB RIF assay in osteoarticular tuberculosis: A retrospective study

Table 1 Categorization of cases according to composite reference standard

Cases	Smear microscopy	Culture	Gene Xpert	ATT course (in mo)	Outcome (SF-12)		CRS category
					PCS-12	MCS-12
Case No. 1	Negative	No growth	Positive	12	48.76	55.50	Probable OATB case
Case No. 2	Negative	Positive	Positive	Lost to follow-up			Confirmed OATB case
Case No. 3	Negative	No growth	Positive	15	46.03	56.9	Probable OATB case
Case No. 4	Negative	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 5	Negative	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 6	Positive	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 7	Negative	No growth	Positive	24	56.57	60.75	Probable OATB case
Case No. 8	Negative	No growth	Positive	24	46.03	56.9	Probable OATB case
Case No. 9	Negative	No growth	Positive	6	48.60	33.57	Probable OATB case
Case No. 10	Positive	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 11	Negative	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 12	Negative	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 13	Negative	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 14	Positive	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 15	Positive	Contamination	Positive	Lost to follow-up			Probable OATB case
Case No. 16	Negative	Contamination	Positive	Lost to follow-up			Probable OATB case
Case No. 17	Negative	No growth	Positive	6	56.57	60.75	Probable OATB case
Case No. 18	Negative	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 19	Negative	No growth	Positive	6	52.23	56.51	Probable OATB case
Case No. 20	Negative	No growth	Positive	21	52.23	56.51	Probable OATB case
Case No. 21	Negative	No growth	Positive	15	52.23	53.63	Probable OATB case
Case No. 22	Positive	Contamination	Positive	12	56.57	60.75	Probable OATB case
Case No. 23	Negative	No growth	Positive	15	48.60	33.57	Probable OATB case
Case No. 24	Negative	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 25	Positive	Positive	Positive	Lost to follow-up			Confirmed OATB case
Case No. 26	Negative	No growth	Positive	12	51.81	48.67	Probable OATB case
Case No. 27	Negative	Positive	Positive	12	48.76	55.50	Confirmed OATB case
Case No. 28	Negative	No growth	Positive	6	56.57	60.75	Probable OATB case
Case No. 29	Negative	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 30	Negative	No growth	Positive	12	51.81	48.67	Probable OATB case
Case No. 31	Negative	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 32	Negative	No growth	Positive	12	40.76	40.94	Probable OATB case
Case No. 33	Negative	No growth	Positive	Lost to follow-up			Probable OATB case
Case No. 34	Negative	Positive	Positive	2	28.93	40.32	Confirmed OATB case
Case No. 35	Negative	No growth	Positive	1.5	28.93	40.32	Probable OATB case
Case No. 36	Negative	Positive	Negative	12	48.76	55.50	Confirmed OATB case
Case No. 37	Negative	No growth	Negative	1.5	28.93	40.32	Possible OATB case

CRS: Composite reference standard; ATT: Anti-tuberculosis treatment; OATB: Osteoarticular tuberculosis; SF-12: Short form survey-12; PCS-12: Physical composite scale-12; MCS-12: Mental health composite scale-12.

Table 2 Demographic and clinical distribution of composite reference standard positive, probable and possible osteoarticular tuberculosis cases, n (%)

Characteristics		Cases (n = 37)
Age group (yr)	0 - 10	1 (2.7)
	11 - 20	5 (13.6)
	21 – 30	10 (27.0)
	31 - 40	6 (16.2)
	41- 50	6 (16.2)
	51 - 60	6 (16.2)
	> 60	3 (8.1)
Sex	Male	19 (51.4)
	Female	18 (48.6)
Site if OATB	Knee	8 (21.6)
	Spine	20 (54.1)
	Elbow	1 (2.7)
	Wrist	1 (2.7)
	Psoas abscess	7 (18.9)

OATB: Osteoarticular tuberculosis.

Table 3 Performance assay and statistical analysis of gene Xpert, culture and, smear microscopy against composite reference standard (n = 40)

Methods	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)	Kappa statistics (% agreement)
Gene Xpert	94.6	100.0	94.6	100.0	95.0
Culture	13.5	100.0	13.5	100.0	20.0
Smear microscopy	16.2	100.0	16.2	100.0	22.5

PPV: Positive predictive value; NPV: Negative predictive value.