However, it is not easy to predict survival in IPF patients who are potentially qualified for lung transplantation, and studies evaluating the role of cardiopulmonary function have been inconsistent. Thus, for example, some reports have suggested that hemodynamics and respiratory function do not predict survival, while others have shown that survival is significantly related to a number of different clinical and functional data, including evidence of pulmonary hypertension on the chest radiograph, reduced lung volume, and the presence of gas exchange abnormalities with exercise.17–18 Moreover, in contradiction to previous reports,19 King et al18 found that diffusing capacity of the lung for carbon monoxide was not an independent predictor of survival in the multivariate analyses. By contrast, others have suggested that in IPF patients < 65 years of age, the best prediction of survival is derived from a combination of the percent predicted for the diffusing capacity of the lung for carbon monoxide and the high-resolution CT scan fibrosis score.14 Several reasons may contribute to these discrepancies, including the natural biological heterogeneity of the disease, the period that has elapsed before diagnosis, and previous medical treatment. Additionally, in some studies all patients were required to undergo a surgical lung biopsy, while in others the diagnosis of disease in a number of patients relied on clinical and high-resolution CT scan findings.14,18 Therefore, in the former studies, the authors probably did not include patients who were too ill or were considered to be at high risk for complications from anesthesia or surgery. Still, the question about which parameters have the best potential for optimizing the timing of referral for transplantation remains open.