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

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 HIV-positive 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.