The diagnosis can be confirmed by lung biopsy. A videoscopic assisted thoracoscopic wedge biopsy (VATS) under general anesthesia may be necessary to obtain enough tissue to make an accurate diagnosis. This kind of biopsy involves placement of several tubes through the chest wall, one of which is used to cut off a piece of lung to send for evaluation. The removed tissue is examined histopathologically by microscopy to confirm the presence and pattern of fibrosis as well as presence of other features that may indicate a specific cause e.g. specific types of mineral dust or possible response to therapy e.g. a pattern of so-called non-specific interstitial fibrosis.

Misdiagnosis is common because, while overall pulmonary fibrosis is not rare, each individual type of pulmonary fibrosis is uncommon and the evaluation of patients with these diseases is complex and requires a multidisciplinary approach. Terminology has been standardized but difficulties still exist in their application. Even experts may disagree with the classification of some cases.

On spirometry, as a restrictive lung disease, both the FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity) are reduced so the FEV1/FVC ratio is normal or even increased in contrast to obstructive lung disease where this ratio is reduced. The values for residual volume and total lung capacity are generally decreased in restrictive lung disease.

Bronchoalveolar lavage (BAL) is a well-tolerated diagnostic procedure in ILD. BAL cytology analyses (differential cell counts) should be considered in the evaluation of patients with IPF at the discretion of the treating physician based on availability and experience at their institution. BAL may reveal alternative specific diagnoses: malignancy, infections, eosinophilic pneumonia, histiocytosis X, or alveolar proteinosis. In the evaluation of patients with suspected IPF, the most important application of BAL is in the exclusion of other diagnoses. Prominent lymphocytosis (>30%) generally allows excluding a diagnosis of IPF.

According to the updated 2011 guidelines, in the absence of a typical UIP pattern on HRCT, a surgical lung biopsy is required for confident diagnosis.

Histologic specimens for the diagnosis of IPF must be taken at least in three different places and be large enough that the pathologist can comment on the underlying lung architecture. Small biopsies, such as those obtained via transbronchial lung biopsy (performed during bronchoscopy) are usually not sufficient for this purpose. Hence, larger biopsies obtained surgically via a thoracotomy or thoracoscopy are usually necessary.

Lung tissue from people with IPF usually show a characteristic histopathologic UIP pattern and is therefore the pathologic counterpart of IPF. Although a pathologic diagnosis of UIP often corresponds to a clinical diagnosis of IPF, a UIP histologic pattern can be seen in other diseases as well, and fibrosis of known origin (rheumatic diseases for example). There are four key features of UIP including interstitial fibrosis in a ‘patchwork pattern’, interstitial scarring, honeycomb changes and fibroblast foci.

Fibroblastic foci are dense collections of myofibroblasts and scar tissue and, together with honeycombing, are the main pathological findings that allow a diagnosis of UIP.

For some types of chILD and few forms adult ILD genetic causes have been identified. These may be identified by blood tests. For a limited number of cases this is a definite advantage, as a precise molecular diagnosis can be done; frequently then there is no need for a lung biopsy. Testing is available for

Investigation is tailored towards the symptoms and signs. A proper and detailed history looking for the occupational exposures, and for signs of conditions listed above is the first and probably the most important part of the workup in patients with interstitial lung disease. Pulmonary function tests usually show a restrictive defect with decreased diffusion capacity (DLCO).

A lung biopsy is required if the clinical history and imaging are not clearly suggestive of a specific diagnosis or malignancy cannot otherwise be ruled out. In cases where a lung biopsy is indicated, a trans-bronchial biopsy is usually unhelpful, and a surgical lung biopsy is often required.

Pulmonary function tests, arterial blood gases, ventilation perfusion relationships, and O2 diffusing capacity are normal in the initial stages of PAM. As the disease progresses, pulmonary function tests reveal typical features of a restrictive defect with reduced forced vital capacity (FVC) and elevated forced expiratory volume in FEV1/FVC.

Hypoxia caused by pulmonary fibrosis can lead to pulmonary hypertension, which, in turn, can lead to heart failure of the right ventricle. Hypoxia can be prevented with oxygen supplementation.

Pulmonary fibrosis may also result in an increased risk for pulmonary emboli, which can be prevented by anticoagulants.

On magnetic resonance imaging (MRI), the calcific lesions usually show hypointensity or a signal void on T1- and T2-weighted images.

Multiple abnormal laboratory findings have been noted in indium lung. High levels of serum indium have been found in all cases of indium lung. Other abnormal laboratory values that have been found include elevated alanine aminotransferase, elevated aspartate aminotransferase, elevated C-reactive protein, elevated interstitial lung disease markers, and elevated GM-CSF autoantibodies.

The major criterion for diagnosis is typically a confirmed surgical biopsy. Minor diagnostic criteria have been proposed for DIPNECH.

- Clinical presentation: woman, between the age of 45 and 67 with cough and/or shortness of breath for 5–10 years

- Pulmonary function: increased residual volume, increased total lung capacity, fixed obstruction, low diffusing capacity of the lung for carbon monoxide that corrects with alveolar volume

- High-resolution CT scan: diffuse pulmonary nodules 4–10 mm, greater than 20 nodules, mosaic attenuation or air trapping in greater than 50% of the lung

- Transbronchial biopsy: proliferation of pulmonary neuroendocrine cells

- Serum markers: elevated serum chromogranin A levels

Although some patients present with normal lung function, pulmonary function tests generally demonstrate fixed airway obstruction with a decreased FEV1 and reduced FEV1/FVC ratio without bronchodilator response. Air trapping is common and leads to increased residual volumes. As the disease progresses, a mixed pattern of obstruction and restriction may develop. In general the obstructive lung disease is slowly progressive with periods of stability.

UIP may be diagnosed by a radiologist using computed tomography (CT) scan of the chest, or by a pathologist using tissue obtained by a lung biopsy. Radiologically, the main feature required for a confident diagnosis of UIP is honeycomb change in the periphery and the lower portions (bases) of the lungs. The histologic hallmarks of UIP, as seen in lung tissue under a microscope by a pathologist, are interstitial fibrosis in a "patchwork pattern", honeycomb change and fibroblast foci (see images below).

The exact cause of rheumatoid lung disease is unknown. However, associated factors could be due largely to smoking. Sometimes, the medicines used to treat rheumatoid arthritis, especially methotrexate, may result in lung disease.

Prevention's:

- Stop smoking: Chemicals found in cigarettes can irritate already delicate lung tissue, leading to further complications.

- Having regular checkups: The doctor could listen to lungs and monitor breathing, because lung problems that are detected early can be easier to treat.

CT scanning and radiography can be used to aid in the diagnosis of indium lung. CT abnormalities include ground-glass opacities, interlobular septal thickening, honeycombing, and bronchiectasis.

Clinically, IPH manifests as a triad of haemoptysis, diffuse parenchymal infiltrates on chest radiographs, and iron deficiency anaemia. It is diagnosed at an average age of 4.5 plus or minus 3.5 years, and it is twice as common in females. The clinical course of IPH is exceedingly variable, and most of the patients continue to have episodes of pulmonary haemorrhage despite therapy. Death may occur suddenly from acute pulmonary haemorrhage or after progressive pulmonary insufficiency resulting in chronic respiratory failure.

The diagnosis of RA was formerly based on detection of rheumatoid factor (RF). However, RF is also associated with other autoimmune diseases. The detection of anti-CCP is currently considered the most specific marker of RA. The diagnosis of rheumatoid lung disease is based on evaluation of pulmonary function, radiology, serology and lung biopsy. High resolution CT scans are preferred to chest X-rays due to their sensitivity and specificity.

Associated doctors to diagnosis this properly would be a Rheumatologists or Pulmonologist.

Within a physical examination doctors could find possible indications, such as hearing crackles (rales) when listening to the lungs with a stethoscope. Or, there may be decreased breath sounds, wheezing, a rubbing sound, or normal breath sounds. When listening to the heart, there may be abnormal heart sounds. Bronchoscopic, video-assisted, or open lung biopsy allows the histological characterization of pulmonary lesions, which can distinguish rheumatoid lung disease from other interstitial lung diseases.

The following tests may also show signs of rheumatoid lung disease:

- Chest x-ray may show:

- pleural effusion

- lower zone predominant reticular or reticulonodular pattern

- volume loss in advanced disease

- skeletal changes, e.g. erosion of clavicles, glenohumeral erosive arthropathy, superior rib notching

- Chest CT or HRCT features include:

- pleural thickening or effusion

- interstitial fibrosis

- bronchiectasis

- bronchiolitis obliterans

- large rheumatoid nodules

- single or multiple

- tend to be based peripherally

- may cavitate (necrobiotic lung nodules)

- cavitation of a peripheral nodule can lead to pneumothorax or haemopneumothorax.

- follicular bronchiolitis

- small centrilobular nodules or tree-in-bud

- rare

- Caplan syndrome

- Echocardiogram (may show pulmonary hypertension)

- Lung biopsy (bronchoscopic, video-assisted, or open), which may show pulmonary lesions

- Lung function tests

- Needle inserted into the fluid around the lung (thoracentesis)

- Blood tests for rheumatoid arthritis

The differential diagnosis includes other types of lung disease that cause similar symptoms and show similar abnormalities on chest radiographs. Some of these diseases cause fibrosis, scarring or honeycomb change. The most common considerations include:

- chronic hypersensitivity pneumonitis

- non-specific interstitial pneumonia

- sarcoidosis

- pulmonary Langerhans cell histiocytosis

- asbestosis

The chest radiograph may appear relatively normal, even late in the disease, or may suggest hyperinflation only. As the disease progresses, the chest radiograph often demonstrates diffuse, bilateral and symmetric reticulonodular opacities, cysts, bullae or a "honeycomb" (i.e., pseudo fibrotic) appearance. Pleural effusion and pneumothorax may be apparent. Preservation of lung volumes in the presence of increased interstitial markings is a radiographic hallmark of LAM that helps distinguish it from most other interstitial lung diseases, in which alveolar septal and interstitial expansion tend to increase the lung’s elastic recoil properties and decreased lung volumes.

The high-resolution computed tomography (HRCT) chest scan is better than the chest radiograph to detect cystic parenchymal disease and is almost always abnormal at the time of diagnosis, even when the chest radiograph and pulmonary function assessments are normal. The typical CT shows diffuse round, bilateral, thin-walled cysts of varying sizes ranging from 1 to 45 mm in diameter. The numbers of cysts varies in LAM from a few to almost complete replacement of normal lung tissue. The profusion of cysts tends to be milder in patients with TSC-LAM than S-LAM, perhaps explained in part because TSC-LAM patients typically receive earlier screening. Pleural effusions are seen on CT in 12% of patients with S-LAM and 6% of patients with TSC-LAM. Other CT features include linear densities (29%), hilar or mediastinal lymphadenopathy (9%), pneumothorax, lymphangiomyoma, and thoracic duct dilation. Ground-glass opacities (12%) suggest the presence of interstitial edema due to lymphatic congestion. In patients with TSC, nodular densities on HRCT may represent multifocal micronodular pneumocyte hyperplasia (MMPH) made up of clusters of hyperplastic type II pneumocytes. MMPH may be present in males or females with TSC in the presence or absence of LAM, but not in patients with S-LAM. MMPH is not typically associated with physiologic or prognostic consequences, but one case of respiratory failure due to MMPH has been reported.

Bronchiectasis may be diagnosed clinically or on review of imaging. The British Thoracic Society recommends all non-cystic-fibrosis-related bronchiectasis be confirmed by CT. CT may reveal tree-in-bud abnormalities, dilated bronchi, and cysts with defined borders.

Other investigations typically performed at diagnosis include blood tests, sputum cultures, and sometimes tests for specific genetic disorders.

Corticosteroids are the mainstay of treatment of IPH, though they are controversial and lack clear evidence in their favour. They are thought to decrease the frequency of haemorrhage, while other studies suggest that they do not have any effect on the course or prognosis of this disease. In either case, steroid therapy has significant side effects. Small trials have investigated the use of other medications, but none has emerged as a clear standard of care. This includes immune modulators such as hydroxychloroquine, azathioprine, and cyclophosphamide. 6-mercaptopurine as a long-term therapy may prevent pulmonary haemorrhage. A 2007 scientific letter. reports preliminary success in preventing pulmonary haemorrhage with the anti-oxidant N-acetylcysteine.

In restrictive lung disease, both forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) are reduced, however, the decline in FVC is more than that of FEV1, resulting in a higher than 80% FEV1/FVC ratio.

In obstructive lung disease however, the FEV1/FVC is less than 0.7, indicating that FEV1 is significantly reduced when compared to the total expired volume. This indicates that the FVC is also reduced, but not by the same ratio as FEV1.

One definition requires a total lung capacity which is 80% or less of the expected value.

According to the American Thoracic Society (ATS), the general diagnostic criteria for asbestosis are:

- Evidence of structural pathology consistent with asbestosis, as documented by imaging or histology

- Evidence of causation by asbestos as documented by the occupational and environmental history, markers of exposure (usually pleural plaques), recovery of asbestos bodies, or other means

- Exclusion of alternative plausible causes for the findings

The abnormal chest x-ray and its interpretation remain the most important factors in establishing the presence of pulmonary fibrosis. The findings usually appear as small, irregular parenchymal opacities, primarily in the lung bases. Using the ILO Classification system, "s", "t", and/or "u" opacities predominate. CT or high-resolution CT (HRCT) are more sensitive than plain radiography at detecting pulmonary fibrosis (as well as any underlying pleural changes). More than 50% of people affected with asbestosis develop plaques in the parietal pleura, the space between the chest wall and lungs. Once apparent, the radiographic findings in asbestosis may slowly progress or remain static, even in the absence of further asbestos exposure. Rapid progression suggests an alternative diagnosis.

Asbestosis resembles many other diffuse interstitial lung diseases, including other pneumoconiosis. The differential diagnosis includes idiopathic pulmonary fibrosis (IPF), hypersensitivity pneumonitis, sarcoidosis, and others. The presence of pleural plaquing may provide supportive evidence of causation by asbestos. Although lung biopsy is usually not necessary, the presence of asbestos bodies in association with pulmonary fibrosis establishes the diagnosis. Conversely, interstitial pulmonary fibrosis in the absence of asbestos bodies is most likely not asbestosis. Asbestos bodies in the absence of fibrosis indicate exposure, not disease.

In the differential diagnosis (finding the correct diagnosis between diseases that have overlapping features) of some obstructive lung diseases, DPB is often considered. A number of DPB symptoms resemble those found with other obstructive lung diseases such as asthma, chronic bronchitis, and emphysema. Wheezing, coughing with sputum production, and shortness of breath are common symptoms in such diseases, and obstructive respiratory functional impairment is found on pulmonary function testing. Cystic fibrosis, like DPB, causes severe lung inflammation, excess mucus production, and infection; but DPB does not cause disturbances of the pancreas nor the electrolytes, as does CF, so the two diseases are different and probably unrelated. DPB is distinguished by the presence of lesions that appear on X-rays as nodules in the bronchioles of both lungs; inflammation in all tissue layers of the respiratory bronchioles; and its higher prevalence among individuals with East Asian lineage.

DPB and bronchiolitis obliterans are two forms of primary bronchiolitis. Specific overlapping features of both diseases include strong cough with large amounts of often pus-filled sputum; nodules viewable on lung X-rays in the lower bronchi and bronchiolar area; and chronic sinusitis. In DPB, the nodules are more restricted to the respiratory bronchioles, while in OB they are often found in the membranous bronchioles (the initial non-cartilaginous section of the bronchiole, that divides from the tertiary bronchus) up to the secondary bronchus. OB is a bronchiolar disease with worldwide prevalence, while DPB has more localized prevalence, predominantly in Japan. Prior to clinical recognition of DPB in recent years, it was often misdiagnosed as bronchiectasia, COPD, IPF, phthisis miliaris, sarcoidosis or alveolar cell carcinoma.

The diagnosis of DPB requires analysis of the lungs and bronchiolar tissues, which can require a lung biopsy, or the more preferred high resolution computed tomography (HRCT) scan of the lungs. The diagnostic criteria include severe inflammation in all layers of the respiratory bronchioles and lung tissue lesions that appear as nodules within the terminal and respiratory bronchioles in both lungs. The nodules in DPB appear as opaque lumps when viewed on X-rays of the lung, and can cause airway obstruction, which is evaluated by a pulmonary function test, or PFT. Lung X-rays can also reveal dilation of the bronchiolar passages, another sign of DBP. HRCT scans often show blockages of some bronchiolar passages with mucus, which is referred to as the "tree-in-bud" pattern. Hypoxemia, another sign of breathing difficulty, is revealed by measuring the oxygen and carbon dioxide content of the blood, using a blood test called arterial blood gas. Other findings observed with DPB include the proliferation of lymphocytes (white blood cells that fight infection), neutrophils, and foamy histiocytes (tissue macrophages) in the lung lining. Bacteria such as "H. influenzae" and "P. aeruginosa" are also detectable, with the latter becoming more prominent as the disease progresses. The white blood, bacterial and other cellular content of the blood can be measured by taking a complete blood count (CBC). Elevated levels of IgG and IgA (classes of immunoglobulins) may be seen, as well as the presence of rheumatoid factor (an indicator of autoimmunity). Hemagglutination, a clumping of red blood cells in response to the presence of antibodies in the blood, may also occur. Neutrophils, beta-defensins, leukotrienes, and chemokines can also be detected in bronchoalveolar lavage fluid injected then removed from the bronchiolar airways of individuals with DPB, for evaluation.