Efficacy of 99mTc-DTPA lung clearance test in the diagnosis of PCP in HIV-positive patients.

The study aims to evaluate the efficacy of technetium-99m diethylenetriaminepentaacetic acid ((99m)Tc-DTPA) lung clearance test in the diagnosis of pneumocystis carinii pneumonia (PCP) in HIV-positive paediatric patients. Twenty HIV-negative patients with no chest symptoms constituted Group A, 25 HIV antibody positive asymptomatic children formed Group B, while 45 HIV antibody positive children with respiratory infections comprised Group C. Group C was subdivided into C(1) (n = 20, documented PCP on microbiology), C(2) (n = 10, tuberculosis) and C(3) (n = 15, bacterial pneumonias). The mean age group of patients in Group A, Group B and Group C was 4.7 +/- 1.9, 4.2 +/- 1.5 and 4.8 +/- 1.7 years, respectively. All patients were subjected to complete blood count, blood culture, chest radiographs, microscopic staining of sputum (PCP stains, Ziehl-Nielsen staining, Gram staining), ABG and Mantoux test. All these patients underwent dynamic lung scans using (99m)Tc-DTPA aerosols and lung clearance was calculated in terms of half-time transfer value (T(1/2)) value. T(1/2) was compared between different groups and lung scan findings were correlated with radiological and microbiological results. Patients with PCP had T(1/2) in the range of 9.02 +/- 1.35, TB 28.2 +/- 3.03 min and other bacterial pneumonias in the range of 20.5 +/- 3.1 min (range for normal individuals was 49.8 +/- 6.13 min). T(1/2) in patients with PCP was found to be significantly lower when compared with T(1/2) in other groups. Patients with PCP had characteristic biphasic curves while the rest had monophasic curves. Some patients with PCP had low T(1/2) values even when chest radiographs and arterial blood gases were normal. (99m)Tc-DTPA lung clearance test is a sensitive, safe and non-invasive diagnostic tool for the early detection of PCP in HIV-positive paediatric patients.