What pulmonary function test result is most characteristic of idiopathic pulmonary fibrosis?

In idiopathic pulmonary fibrosis (IPF), the most characteristic pulmonary function test finding is a reduced FEV1/FVC ratio, indicating a restrictive lung pattern. This is represented by a ratio around 0.6, which suggests that both the FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity) are decreased, but FVC generally decreases more significantly than FEV1, thus leading to a preserved or even increased ratio in some cases.

IPF leads to lung stiffness and impaired expansion, resulting in limitations in the total volume of air the lungs can hold and how effectively air can be expelled. Therefore, the restrictive pattern of lung disease is best characterized by this decrease in the FEV1/FVC ratio associated with radiological findings typical of IPF, such as honeycombing and ground-glass opacities on high-resolution CT scans.

The other pulmonary function test results listed do not align with the typical presentation of IPF. While an elevated residual volume may indicate air trapping, it is more characteristic of obstructive pulmonary diseases. Likewise, a low peak flow is not specific to IPF and typically indicates flow limitation found in asthma or COPD. The transfer factor (DLCO) being at