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Updated: Aug 18, 2026
Diagnosing Pulmonary Tuberculosis with the Xpert MTB/RIF Test
Published on: April 9, 2012
Detection of pulmonary tuberculosis in patients with a normal chest radiograph
D D Marciniuk1, B D McNab, W T Martin
1Division of Tuberculosis Control, The Research Center for the Elimination of Tuberculosis, Royal University Hospital, University of Saskatchewan, Saskatoon, Canada.
Objectives:
To describe the early symptoms of pulmonary tuberculosis (TB) when the chest radiograph (CXR) is normal.
Setting:
Centralized, provincial TB control program.
Subjects:
Twenty-five patients with culture-positive pulmonary TB and a normal CXR were identified from a review of 518 consecutive patients with culture-positive pulmonary TB in the province of Saskatchewan from January 1, 1988 to March 31, 1997. Patients with abnormal CXRs at the time of diagnosis were excluded from the analysis.
Results:
Twenty-three of the 25 patients (92%) were symptomatic at the time of diagnosis, with cough/sputum (76%) being reported most commonly. Eleven patients were identified because of contact tracing from cases of infectious pulmonary TB, while the other 14 patients were identified because of an investigation of symptoms. Twenty-four patients (96%) exhibited one or more symptoms of cough for > 1 month, fever for > 1 week, or skin-test conversion after contact with infectious TB. The sputum smear of only one patient was positive. Two patients were pregnant at the time of diagnosis, one patient was HIV-positive, and one patient demonstrated isoniazid-resistant organisms on sensitivity testing. Five patients were diagnosed as having primary TB associated with Mantoux skin-test conversion. The incidence of culture-positive pulmonary TB with a normal chest radiograph was < 1% in the period from 1988 to 1989 and steadily increased to 10% in the period from 1996 to 1997.
Conclusions:
Culture-positive pulmonary TB with a normal CXR is not uncommon, and the incidence of this presentation is increasing. Patients with this presentation of TB are typically symptomatic and/or are detected by contact tracing to infectious cases of pulmonary TB. The results suggest that patients presenting with a cough for > 1 month, with a fever for > 1 week, or with documented skin-test conversion < 2 years after known exposure to infectious TB should have sputum submitted for a Mycobacterium tuberculosis smear and culture despite a normal CXR.
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