Lung Clearance of Inhaled $^{99m}Tc$ -DTPA by Urine Excretion Ratio

Background: Lung clearance of inhaled -DTPA reflects alveolar epithelial permeability and it had been reported as more sensitive than conventional pulmonary function tests in detecting lung epithelial damage. However, measuring lung clearance of inhaled -DTPA by gamma camera may not always reflect alveolar epithelial permeability exactly because it is influenced by mucociliary clearance depending on the site of particle deposition. Moreover, this method takes much time and patient's effort because he has to sit or lie still in front of the camera for a prolonged period. Most of the absorbed DTPA is excreted in urine within 24 hours and the amount of excreted DTPA in urine during the first few hours after inhalation is influenced by absorption rate which is correlated with the alveolar-epithelial permeability suggesting that the urinary excretion, especially in first few hours, may be an alternate index for lung clearance. The purpose of this study was to evaluate the usefulness of ratio of excreted -DTPA in 2 hour and 24 hour urine as an index of alveolar-epithelial damage. Methods: Pulmonary function tests including diffusing capacity and lung clearance of -DTPA measured by gama camera () and 2hr/24hr urine excretion ratio (Ratio) of inhaled -DTPA in 8 normal subjects and 14 patients with diffuse interstitial lung disease were compared. Results: 1) In the normal control, there was significant negative correlation between the and the Ratio (r=-0.77, p and Ratio(r=-0.63, p was min which was significantly lower than that of normal control, min and the Ratio was also signifantly higher than that of the normal control, (p or Ratio and diffusing capactiy of lung in both patients and controls (p>0.05). Conclusion: These results suggests that 2hr/24hr urine excretion ratio of inhaled -DTPA is a useful simple bedside test in assessing alveolar epithelial permeability and that it may be used as an additive follow-up test in patients with diffuse interstitial lung disease complementing conventional pulmonary function tests.