The Role of Gallium-67 Scintigraphy and High Resolution Computed Tomography as Predictors of Disease Activity in Sputum Smear Negative Pulmonary Tuberculosis

To determine the role of gallium-67 scintigraphy and high resolution computed tomography (HRCT) findings as predictors of disease activity in sputum smear negative patients with pulmonary tuberculosis, 30 hospitalised patients suspected of having active pulmonary tuberculosis on the basis of upper lobe infiltrates in the chest x-rays were studied prospectively. Ga-67 citrate scanning and HRCT were performed at the beginning of the study. Patchy unilateral or bilateral air-space consolidation, cavitation and a tree in bud appearance were accepted as activity criteria in HRCT. Gallium-67 uptake ratio (GR) and visual scoring were taken as the criteria in assessing gallium-67 imaging. The sensitivity and specificity of Ga-67 scintigraphy in assessing the activity of pulmonary TB were 83.3% and 58.3%, while the sensitivity and specificity of HRCT in assessing the activity of pulmonary TB were 100% and 66.7%, respectively. Using these techniques together the sensitivity increased to 100% while specificity was 50%. Though the positive predictive value (PPV) of this assessment was 75%, a negative predictive value (NPV) of 100% was found. The results indicate that the use of both GA-67 scintigraphy and HRCT scans will be helpful in determining disease activity in sputum smear negative pulmonary tuberculosis patients. When the two methods are used together, a negative predictive value of 100% is reached, a finding which suggests that both of these techniques must be used to rule out active disease.