Table 2 Performance of Genotype MTBDRplus at different ramp rates for the detection of M. tuberculosis-complex DNA (TUB-band), stratified by smear status, when done directly on sputa from Xpert MTB/RIF-positive patients. Genolysed extract from each specimen was tested at each ramp rate. TUB-band detection and the rate of indeterminates worsened in smear-negative specimens with use of the incorrect ramp rate.

From: Widespread use of incorrect PCR ramp rate negatively impacts multidrug-resistant tuberculosis diagnosis (MTBDRplus)

Smear microscopy status Ramp rate (°C/s) TUB-band positive (%) Determinate (%) Indeterminate (%)
Positive n = 52 4.0 52/52 (100) 52/52 (100) 0/52 (0)
2.2* 52/52 (100) 52/52 (100) 0/52 (0)
Negative n = 55 4.0 32/55 (58) 27/32 (84) 5/32 (16)
2.2* 42/55 (76) (p = 0.042) 41/42 (98) (p = 0.164) 1/42 (2) (p = 0.039)
  1. P-values are for comparisons between ramp rates for smear-negative specimens.
  2. *Manufacturer-recommended ramp rate.