Prediction of survival in interstitial lung disease (ILD); role of DTPA lung clearance scans and lung function variables

Introduction: A variety of lung function, radiological and inflammatory markers are used to predict the clinical course of ILD. The perceived value of 99m Technetium-labelled diethylenetriamine penta-acetic acid (DTPA) clearance as one of these has waxed and waned over 20 years or more. One deficit has been the lack of long term studies addressing the value of DTPA clearance in predicting overall survival. Aim: To determine whether DTPA lung clearance predicts survival in ILD independent of lung function. Methods: We analysed DTPA lung clearance scans performed in the assessment of ILD at Concord Hospital from Jan 2000 to Dec 2010. Normal clearance was t 1/2 >25 minutes with mono-exponential pattern. Overall survival for normal and abnormal groups was evaluated using Kaplan-Meier method and the log-rank test and Cox proportional hazards regression models. Results: 227 DTPA scans were performed for initial assessment of ILD in the study period. 56% of subjects were male and the mean age at initial scan was 71 (13). Diagnoses were idiopathic pulmonary fibrosis in 89(39%), unspecified ILD in 54(24%), connective tissue disease-related ILD in 37(16%) and ILD/COPD in 20(9%). In univariate analysis, rapid DTPA clearance, hazard ratios (HR; 95% CI) 1.88 (1.11 - 3.18), DLCO Conclusions: Although rapid DTPA clearance predicts poorer survival in patients being initially evaluated for ILD, the predictive value of DTPA is embedded in DLCO.