The place of lung 99mTc DTPA aerosol transfer in the investigation of lung infections in HIV positive patients

Pneumocystis carinii pneumonia (PCP) is the most common cause of pneumonia in HIV antibody positive patients, but other pneumonias remain important, i.e. streptococcal and mycobacterial infections. A definitive diagnosis relies on obtaining samples from the lung either noninvasively (induced sputum), or invasively (bronchoalveolar lavage, transbronchial or open lung biopsy). We have used the noninvasive technique of nebulized 99mTc DTPA transfer, to assess patients with PCP (n = 30) and other lung infections (n = 20) to see whether this test will distinguish between the various infections. The presence of a biphasic, rapid transfer curve indicates severe extensive alveolar damage and is seen in PCP or legionella pneumonia. The mean transfer time (T50 +/- SEM) for patients with PCP (whether smokers or nonsmokers) was 2.1 +/- 0.2 min, and for two of the patients with legionella 3.2 min. In PCP effective treatment causes the transfer to slow (mean T50 22.7 +/- 3.3 min, n = 24) and become monoexponential. Other causes of these changes in transfer are discussed. The other pneumonias (streptococcal, mycobacterial, and staphylococcal) did not result in biphasic curves or very rapid times, their T50 values are indistinguishable from cigarette smokers. In this patient group the DTPA transfer is a useful noninvasive investigation with a very rapid, biphasic curve indicating a high probability of PCP.