Pulmonary 99mTc-DTPA aerosol clearance and survival in usual interstitial pneumonia (UIP)

Background-Clearance of inhaled technetium 99m-labelled diethylenetriamine penta-acetic acid (Tc-99m-DTPA) from the lungs is a potential indicator of disease progression in patients with idiopathic pulmonary fibrosis (IPF). Methods-We prospectively analysed the usefulness of this technique for predicting survival in 106 non-smoking patients with usual interstitial pneumonia (UIP) pattern IPF diagnosed by high resolution CT (HRCT) scanning or histological examination (M/F 65/41, mean (SD) age 61 (11) years). DTPA clearance was analysed according to both mono-exponential and bi-exponential models. Half times for the fast (t(0.5)F) and slow (t(0.5)S) components of clearance, the percentage contribution of the fast component (fF), and half time for mono-exponential approximation to the early part of the clearance curve (t(0.5)) were calculated. Results-The patients had substantially faster t(0.5) (mean 23.9 (9.6) minutes) than normal values (> 45 minutes). Thirty seven patients (35%) died during follow up (median 15 months). Univariate Cox regression analysis identified significant predictors of survival as age, forced expiratory volume in 1 second (FEV1) , forced vital capacity (FVC), total lung capacity (TLC), % predicted TLC, carbon monoxide transfer factor (T-LCO), % predicted TLCO, arterial oxygen tension (Pao(2)), oxygen saturation, t(0.5)F, and HRCT fibrosis score. Multiple stepwise Cox regression analysis identified t(0.5)F (p=0.03, hazard ratio 0.747, 95% CI 0.578 to 0.964), % predicted TLC (p=0.02, hazard ratio 0.976, 95% CI 0.956 to 0.995), % predicted TLCO (p=0.003, hazard ratio 0.960, 95% CI 0.935 to 0.986), and age (p=0.003, hazard ratio 1.062, 95% CI 1.021 to 1.104) as independent predictors of survival. Conclusion-These data suggest that Tc-99m-DTPA clearance t(0.5)F measurement may predict survival in patients with UIP pattern IPF.