Clinical information is key to the interpretation of HRCT scans, as the likelihood that specific radiologic features reflect IPF is not absolute, but dependent on the clinical context. Indeed, making a diagnosis of IPF specifically requires the exclusion of known causes of ILD, including autoimmune diseases, exposure to potential inducers of chronic hypersensitivity pneumonitis, occupational exposures, and the use of certain drugs [
26]. To assist the radiologist in contributing to the MDD, it is important that they have access to relevant information on the patient’s clinical history, exposures and the results of other tests that have been performed (Table
1). While the radiologist does not need to know every detail, if the pulmonologist or other clinician involved in the care of the patient has suspicions as to the cause of the patient’s lung disease, it is valuable for the radiologist to be made aware of them prior to the MDD. For example, laboratory tests may reveal the presence of autoantibodies suggestive of an autoimmune disease (e.g., antinuclear antibodies, anti-cyclic citrullinated peptide, rheumatoid factor) [
1,
11], while serologic testing for IgG antibodies against potential antigens can provide supportive evidence for hypersensitivity pneumonitis [
9,
27]. It is important that clinicians perform a thorough patient interview to ascertain exposures to potential inducers of hypersensitivity pneumonitis such as avian antigens or microbial agents, as chronic hypersensitivity pneumonitis may have a similar clinical and radiological presentation to IPF [
9,
27,
28]. Environmental exposures that increase the risk of ILD include asbestos, metal or wood dust, and farming [
1]. A clinical judgment may need to be made as to whether exposure to such factors is the cause of the ILD, or simply a background exposure in a patient who has developed an idiopathic interstitial pneumonia. Information on any prescribed medications should also be provided to the radiologist. Therapies that have been associated with a UIP-like pattern of pulmonary toxicity include chemotherapeutic agents, antiarrhythmic drugs, and immunosuppressive agents [
29].
The typical presentation of IPF is a male ex-smoker over the age of 50 years who presents with chronic exertional dyspnea and cough and has “Velcro”-like bibasilar inspiratory crackles on auscultation of the chest [
1,
30,
31]. In patients with IPF, pulmonary function tests (PFTs) typically demonstrate a restrictive pattern (i.e., reduced total lung capacity, FVC, and diffusing capacity for carbon monoxide [DL
CO] with a normal ratio of forced expiratory volume in one second [FEV
1] to FVC) [
32,
33]. However, it should be noted that some patients with IPF have an almost normal FVC% predicted early in the course of their disease [
34] and that patients who began with an FVC of over 100% predicted may have lost a substantial amount of lung function and still have an FVC% predicted that appears normal. Further, it should be remembered that concomitant emphysema, which is present in about a third of patients with IPF, increases FVC [
35].
A family history of pulmonary fibrosis should prompt consideration of familial interstitial pneumonia, although this is very rare [
1]. Several mutations have been associated with an increased risk of IPF including those in genes for surfactant proteins (SFTPA2, SFTPC), telomerase reverse transcriptase (TERT), the RNA component of telomerase (TERC), and TOLLIP and MUC5B, which play important roles in lung host defense [
36,
37]. Interestingly, there is emerging evidence that different polymorphisms may be associated with different patterns of fibrosis on HRCT [
38].