Derendinger, B.de Vos, M.Nathavitharana, R. R.Dolby, T.Simpson, J. A.van Helden, P. D.Warren, R. M.Theron, G.2018-03-202018Derendinger, B., M. de Vos, R. R. Nathavitharana, T. Dolby, J. A. Simpson, P. D. van Helden, R. M. Warren, and G. Theron. 2018. “Widespread use of incorrect PCR ramp rate negatively impacts multidrug-resistant tuberculosis diagnosis (MTBDRplus).” Scientific Reports 8 (1): 3206. doi:10.1038/s41598-018-21458-y. http://dx.doi.org/10.1038/s41598-018-21458-y.http://nrs.harvard.edu/urn-3:HUL.InstRepos:35014967The scale-up of rapid drug resistance testing for TB is a global priority. MTBDRplus is a WHO-endorsed multidrug-resistant (MDR)-TB PCR assay with suboptimal sensitivities and high indeterminate rates on smear-negative specimens. We hypothesised that widespread use of incorrect thermocycler ramp rate (speed of temperature change between cycles) impacts performance. A global sample of 72 laboratories was surveyed. We tested 107 sputa from Xpert MTB/RIF-positive patients and, separately, dilution series of bacilli, both at the manufacturer-recommended ramp rate (2.2 °C/s) and the most frequently reported incorrect ramp rate (4.0 °C/s). Mycobacterium tuberculosis-complex DNA (TUB-band)-detection, indeterminate results, accuracy, and inter-reader variability (dilution series only) were compared. 32 respondents did a median (IQR) of 41 (20–150) assays monthly. 78% used an incorrect ramp rate. On smear-negative sputa, 2.2 °C/s vs. 4.0 °C/s improved TUB-band positivity (42/55 vs. 32/55; p = 0.042) and indeterminate rates (1/42 vs. 5/32; p = 0.039). The actionable results (not TUB-negative or indeterminate; 41/55 vs. 28/55) hence improved by 21% (95% CI: 9–35%). Widespread use of incorrect ramp rate contributes to suboptimal MTBDRplus performance on smear-negative specimens and hence limits clinical utility. The number of diagnoses (and thus the number of smear-negative patients in whom DST is possible) will improve substantially after ramp rate correction.en-USJournal Article2018-03-2010.1038/s41598-018-21458-y