Radioactively labelled diethylene triamine penta acetate lung scan in Pneum ocystis carinii pneumonia and asymptomatic HIV-positive patients

Abstract

The objective of this study is to establish normal ranges for the assessment of lung permeability, using 99mTc DTPA (diethylene triamine penta acetate) aerosol by measuring the half-time of transfer from the lung in asymptomatic HIV-positive patients. Also to audit the use of the test in the clinical management of outpatients with symptoms suggestive of Pneumocystis carinii pneumonia (PCP). A retrospective analysis of data from outpatients' notes for the audit of symptomatic patients, and prospective acquisition of 'normal' data for HIVpositive asymptomatic patients who were non-smokers and smokers was performed. Over a period of 8 years, DTPA scans were performed on 400 asymptomatic HIV-positive patients (121 non-smokers and 279 smokers) and 188 symptomatic HIV-positive patients with symptoms suggestive of PCP. A biphasic curve of transfer of 99mTc DTPA with a half-time of less than 4 min, was considered diagnostic of PCP. The mean half-times ( SEM) for asymptomatic non-smokers was 61.4 3 min and for smokers was 21.9 0.8 min. In the symptomatic patients, 106 were treated for PCP and in 97 (91.5%) of these, the transfer was biphasic. Of the remaining 82 patients with respiratory pathology other than PCP, 71 (86.6%) had normal scans. The results show that smokers may have abnormal baseline scans 16/ 279 (5.7%) and therefore a baseline scan before symptoms should be recorded or a higher false positive rate can be expected. The test is however highly sensitive for the detection of PCP and allows the attending physician to initiate PCP treatment without delay.