COPD may need to be differentiated from other causes of shortness of breath such as congestive heart failure, pulmonary embolism, pneumonia, or pneumothorax. Many people with COPD mistakenly think they have asthma. The distinction between asthma and COPD is made on the basis of the symptoms, smoking history, and whether airflow limitation is reversible with bronchodilators at spirometry. Tuberculosis may also present with a chronic cough and should be considered in locations where it is common. Less common conditions that may present similarly include bronchopulmonary dysplasia and obliterative bronchiolitis. Chronic bronchitis may occur with normal airflow and in this situation it is not classified as COPD.

A chest X-ray and complete blood count may be useful to exclude other conditions at the time of diagnosis. Characteristic signs on X-ray are overexpanded lungs, a flattened diaphragm, increased retrosternal airspace, and bullae, while it can help exclude other lung diseases, such as pneumonia, pulmonary edema, or a pneumothorax. A high-resolution computed tomography scan of the chest may show the distribution of emphysema throughout the lungs and can also be useful to exclude other lung diseases. Unless surgery is planned, however, this rarely affects management. An analysis of arterial blood is used to determine the need for oxygen; this is recommended in those with an FEV less than 35% predicted, those with a peripheral oxygen saturation less than 92%, and those with symptoms of congestive heart failure. In areas of the world where alpha-1 antitrypsin deficiency is common, people with COPD (particularly those below the age of 45 and with emphysema affecting the lower parts of the lungs) should be considered for testing.

Respiratory diseases may be investigated by performing one or more of the following tests

- Biopsy of the lung or pleura

- Blood test

- Bronchoscopy

- Chest x-ray

- Computed tomography scan, including high-resolution computed tomography

- Culture of microorganisms from secretions such as sputum

- Ultrasound scanning can be useful to detect fluid such as pleural effusion

- Pulmonary function test

- Ventilation—perfusion scan

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.

Respiratory disease is a common and significant cause of illness and death around the world. In the US, approximately 1 billion "common colds" occur each year. A study found that in 2010, there were approximately 6.8 million emergency department visits for respiratory disorders in the U.S. for patients under the age of 18. In 2012, respiratory conditions were the most frequent reasons for hospital stays among children.

In the UK, approximately 1 in 7 individuals are affected by some form of chronic lung disease, most commonly chronic obstructive pulmonary disease, which includes asthma, chronic bronchitis and emphysema.

Respiratory diseases (including lung cancer) are responsible for over 10% of hospitalizations and over 16% of deaths in Canada.

In 2011, respiratory disease with ventilator support accounted for 93.3% of ICU utilization in the United States.

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.

Chronic obstructive pulmonary disease (COPD), also known as chronic obstructive airways disease (COAD) or chronic airflow limitation (CAL), is a group of illnesses characterised by airflow limitation that is not fully reversible. The flow of air into and out of the lungs is impaired. This can be measured with breathing devices such as a peak flow meter or by spirometry. The term COPD includes the conditions emphysema and chronic bronchitis although most patients with COPD have characteristics of both conditions to varying degrees. Asthma being a reversible obstruction of airways is often considered separately, but many COPD patients also have some degree of reversibility in their airways.

In COPD, there is an increase in airway resistance, shown by a decrease in the forced expiratory volume in 1 second (FEV1) measured by spirometry. COPD is defined as a forced expiratory volume in 1 second to forced vital capacity ratio (FEV1/FVC) that is less than 0.7. The residual volume, the volume of air left in the lungs following full expiration, is often increased in COPD, as is the total lung capacity, while the vital capacity remains relatively normal. The increased total lung capacity (hyperinflation) can result in the clinical feature of a "barrel chest" - a chest with a large front-to-back diameter that occurs in some individuals with COPD. Hyperinflation can also be seen on a chest x-ray as a flattening of the diaphragm.

The most common cause of COPD is cigarette smoking. COPD is a gradually progressive condition and usually only develops after about 20 pack-years of smoking. COPD may also be caused by breathing in other particles and gases.

The diagnosis of COPD is established through spirometry although other pulmonary function tests can be helpful. A chest x-ray is often ordered to look for hyperinflation and rule out other lung conditions but the lung damage of COPD is not always visible on a chest x-ray. Emphysema, for example can only be seen on CT scan.

The main form of long term management involves the use of inhaled bronchodilators (specifically beta agonists and anticholinergics) and inhaled corticosteroids. Many patients eventually require oxygen supplementation at home. In severe cases that are difficult to control, chronic treatment with oral corticosteroids may be necessary, although this is fraught with significant side-effects.

COPD is generally irreversible although lung function can partially recover if the patient stops smoking. Smoking cessation is an essential aspect of treatment. Pulmonary rehabilitation programmes involve intensive exercise training combined with education and are effective in improving shortness of breath. Severe emphysema has been treated with lung volume reduction surgery, with some success in carefully chosen cases. Lung transplantation is also performed for severe COPD in carefully chosen cases.

Alpha 1-antitrypsin deficiency is a fairly rare genetic condition that results in COPD (particularly emphysema) due to a lack of the antitrypsin protein which protects the fragile alveolar walls from protease enzymes released by inflammatory processes.

Significant cases of subcutaneous emphysema are easy to diagnose because of the characteristic signs of the condition. In some cases, the signs are subtle, making diagnosis more difficult. Medical imaging is used to diagnose the condition or confirm a diagnosis made using clinical signs. On a chest radiograph, subcutaneous emphysema may be seen as radiolucent striations in the pattern expected from the pectoralis major muscle group. Air in the subcutaneous tissues may interfere with radiography of the chest, potentially obscuring serious conditions such as pneumothorax. It can also reduce the effectiveness of chest ultrasound. On the other hand, since subcutaneous emphysema may become apparent in chest X-rays before a pneumothorax does, its presence may be used to infer that of the latter injury. Subcutaneous emphysema can also be seen in CT scans, with the air pockets appearing as dark areas. CT scanning is so sensitive that it commonly makes it possible to find the exact spot from which air is entering the soft tissues. In 1994, M.T. Macklin and C.C. Macklin published further insights into the pathophysiology of spontaneous Macklin's Syndrome occurring from a severe asthmatic attack.

The presence of subcutaneous emphysema in a person who appears quite ill and febrile after bout of vomiting followed by left chest pain is very suggestive of the diagnosis of Boerhaave's syndrome, which is a life-threatening emergency caused by rupture of the distal esophagus.

The prevalence of pulmonary interstitial emphysema widely varies with the population studied. In a 1987 study 3% of infants admitted to the neonatal intensive care unit (NICU) developed pulmonary interstitial emphysema.

Pulmonary interstitial emphysema often resolves gradually and may take 2–3 weeks. For longer durations of PIE the length of time of mechanical ventilation needed may increase and the incidence of bronchopulmonary dysplasia becomes higher. Some infants may develop chronic lobar emphysema, which may require surgical lobectomies.

Pneumomediastinum is uncommon and occurs when air leaks into the mediastinum. The diagnosis can be confirmed via chest X-ray showing a radiolucent outline around the heart and mediastinum or via CT scanning of the thorax.

The specific criteria for diagnosis of CPA are:

Chest X-rays showing one or more lung cavities. There may be a fungal ball present or not.

Symptoms lasting more than 3 months, usually including weight loss, fatigue, cough, coughing blood (haemoptysis) and breathlessness

A blood test or tissue fluid test positive for Aspergillus species

Aspergilloma

An aspergilloma is a fungal mass caused by a fungal infection with Aspergillus species that grows in either scarred lungs or in a pre-existing lung cavity, which may have been caused by a previous infection. Patients with a previous history of tuberculosis, sarcoidosis, cystic fibrosis or other lung disease are most susceptible to an aspergilloma. Aspergillomas may have no specific symptoms but in many patients there is some coughing up of blood called haemoptysis - this may be infrequent and in small quantity, but can be severe and then it requires urgent medical help.

Tests used to diagnose an aspergilloma may include:

- Chest X-ray

- Chest CT

- Sputum culture

- Bronchoscopy or bronchoscopy with lavage (BAL)

- Serum precipitins for aspergillus (blood test to detect antibodies to aspergillus)

Almost all aspergillomas are caused by "Aspergillus fumigatus". In diabetic patients it may be caused by "Aspergillus niger". It is very rarely caused by "Aspergillus flavus", "Aspergillus oryzae", "Aspergillus terreus" or "Aspergillus nidulans".

Asthma is an obstructive lung disease where the bronchial tubes (airways) are extra sensitive (hyperresponsive). The airways become inflamed and produce excess mucus and the muscles around the airways tighten making the airways narrower. Asthma is usually triggered by breathing in things in the air such as dust or pollen that produce an allergic reaction. It may be triggered by other things such as an upper respiratory tract infection, cold air, exercise or smoke. Asthma is a common condition and affects over 300 million people around the world.

Asthma causes recurring episodes of wheezing, breathlessness, chest tightness, and coughing, particularly at night or in the early morning.

- Exercise-Induced Asthma — is common in asthmatics, especially after participation in outdoor activities in cold weather.

- Occupational Asthma — An estimated 2% to 5% of all asthma episodes may be caused by exposure to a specific sensitizing agent in the workplace.

- Nocturnal Asthma — is a characteristic problem in poorly controlled asthma and is reported by more than two thirds of sub-optimally treated patients.

A peak flow meter can record variations in the severity of asthma over time. Spirometry, a measurement of lung function, can provide an assessment of the severity, reversibility, and variability of airflow limitation, and help confirm the diagnosis of asthma.

Computed tomography (CT, or "CAT scan") is not necessary for the diagnosis of pneumothorax, but it can be useful in particular situations. In some lung diseases, especially emphysema, it is possible for abnormal lung areas such as bullae (large air-filled sacs) to have the same appearance as a pneumothorax on chest X-ray, and it may not be safe to apply any treatment before the distinction is made and before the exact location and size of the pneumothorax is determined. In trauma, where it may not be possible to perform an upright film, chest radiography may miss up to a third of pneumothoraces, while CT remains very sensitive.

A further use of CT is in the identification of underlying lung lesions. In presumed primary pneumothorax, it may help to identify blebs or cystic lesions (in anticipation of treatment, see below), and in secondary pneumothorax it can help to identify most of the causes listed above.

The diagnosis is based upon a history of symptoms after exposure to the allergen and clinical tests. A physician may take blood tests, seeking signs of inflammation, a chest X-ray and lung function tests. The sufferer shows a restrictive loss of lung function.

Precipitating IgG antibodies against fungal or avian antigens can be detected in the laboratory using the traditional Ouchterlony immunodiffusion method wherein 'precipitin' lines form on agar plate. The ImmunoCAP technology has replaced this time consuming, labor-intensive method with their automated CAP assays and FEIA (Fluorescence enzyme immunoassay) that can detect IgG antibodies against Aspergillus fumigatus (Farmer's lung or for ABPA) or avian antigens (Bird Fancier's Lung).

Although overlapping in many cases, hypersensitivity pneumonitis may be distinguished from occupational asthma in that it is not restricted to only occupational exposure, and that asthma generally is classified as a type I hypersensitivity. Unlike asthma, hypersensitivity pneumonitis targets lung alveoli rather than bronchi.

Ultrasound is commonly used in the evaluation of people who have sustained physical trauma, for example with the FAST protocol. Ultrasound may be more sensitive than chest X-rays in the identification of pneumothorax after blunt trauma to the chest. Ultrasound may also provide a rapid diagnosis in other emergency situations, and allow the quantification of the size of the pneumothorax. Several particular features on ultrasonography of the chest can be used to confirm or exclude the diagnosis.

Subcutaneous emphysema is usually benign. Most of the time, SCE itself does not need treatment (though the conditions from which it results may); however, if the amount of air is large, it can interfere with breathing and be uncomfortable. It occasionally progresses to a state "Massive Subcutaneous Emphysema" which is quite uncomfortable and requires surgical drainage. When the amount of air pushed out of the airways or lung becomes massive, usually due to positive pressure ventilation, the eyelids swell so much that the patient cannot see. Also the pressure of the air may impede the blood flow to the areolae of the breast and skin of the scrotum or labia. This can lead to necrosis of the skin in these areas. The latter are urgent situations requiring rapid, adequate decompression. Severe cases can compress the trachea and do require treatment.

In severe cases of subcutaneous emphysema, catheters can be placed in the subcutaneous tissue to release the air. Small cuts, or "blow holes", may be made in the skin to release the gas. When subcutaneous emphysema occurs due to pneumothorax, a chest tube is frequently used to control the latter; this eliminates the source of the air entering the subcutaneous space. If the volume of subcutaneous air is increasing, it may be that the chest tube is not removing air rapidly enough, so it may be replaced with a larger one. Suction may also be applied to the tube to remove air faster. The progression of the condition can be monitored by marking the boundaries with a special pencil for marking on skin.

Since treatment usually involves dealing with the underlying condition, cases of spontaneous subcutaneous emphysema may require nothing more than bed rest, medication to control pain, and perhaps supplemental oxygen. Breathing oxygen may help the body to absorb the subcutaneous air more quickly.

The tissues in the mediastinum will slowly resorb the air in the cavity so most pneumomediastinums are treated conservatively. Breathing high flow oxygen will increase the absorption of the air.

If the air is under pressure and compressing the heart, a needle may be inserted into the cavity, releasing the air.

Surgery may be needed to repair the hole in the trachea, esophagus or bowel.

If there is lung collapse, it is imperative the affected individual lies on the side of the collapse, although painful, this allows full inflation of the unaffected lung.

Lung biopsies can be diagnostic in cases of chronic hypersensitivity pneumonitis, or may help to suggest the diagnosis and trigger or intensify the search for an allergen. The main feature of chronic hypersensitivity pneumonitis on lung biopsies is expansion of the interstitium by lymphocytes accompanied by an occasional multinucleated giant cell or loose granuloma.

When fibrosis develops in chronic hypersensitivity pneumonitis, the differential diagnosis in lung biopsies includes the idiopathic interstitial pneumonias. This group of diseases includes usual interstitial pneumonia, non-specific interstitial pneumonia and cryptogenic organizing pneumonia, among others.

The prognosis of some idiopathic interstitial pneumonias, e.g. idiopathic usual interstitial pneumonia (i.e. idiopathic pulmonary fibrosis), are very poor and the treatments of little help. This contrasts the prognosis (and treatment) for hypersensitivity pneumonitis, which is generally fairly good if the allergen is identified and exposures to it significantly reduced or eliminated. Thus, a lung biopsy, in some cases, may make a decisive difference.

There are three key elements to the diagnosis of silicosis. First, the patient history should reveal exposure to sufficient silica dust to cause this illness. Second, chest imaging (usually chest x-ray) that reveals findings consistent with silicosis. Third, there are no underlying illnesses that are more likely to be causing the abnormalities. Physical examination is usually unremarkable unless there is complicated disease. Also, the examination findings are not specific for silicosis. Pulmonary function testing may reveal airflow limitation, restrictive defects, reduced diffusion capacity, mixed defects, or may be normal (especially without complicated disease). Most cases of silicosis do not require tissue biopsy for diagnosis, but this may be necessary in some cases, primarily to exclude other conditions.

For uncomplicated silicosis, chest x-ray will confirm the presence of small ( 1 cm) occurs from coalescence of small opacities, particularly in the upper lung zones. With retraction of the lung tissue, there is compensatory emphysema. Enlargement of the hilum is common with chronic and accelerated silicosis. In about 5–10% of cases, the nodes will calcify circumferentially, producing so-called "eggshell" calcification. This finding is not pathognomonic (diagnostic) of silicosis. In some cases, the pulmonary nodules may also become calcified.

A computed tomography or CT scan can also provide a mode detailed analysis of the lungs, and can reveal cavitation due to concomitant mycobacterial infection.

The best way to prevent silicosis is to identify work-place activities that produce respirable crystalline silica dust and then to eliminate or control the dust ("primary prevention"). Water spray is often used where dust emanates. Dust can also be controlled through dry air filtering.

Following observations on industry workers in Lucknow (India), experiments on rats found that jaggery (a traditional sugar) had a preventive action against silicosis.

Patients with single aspergillomas generally do well with surgery to remove the aspergilloma, and are best given pre-and post-operative antifungal drugs. Often, no treatment is necessary. However, if a patient coughs up blood (haemoptysis), treatment may be required (usually angiography and embolisation, surgery or taking tranexamic acid). Angiography (injection of dye into the blood vessels) may be used to find the site of bleeding which may be stopped by shooting tiny pellets into the bleeding vessel.

For chronic cavitary pulmonary aspergillosis and chronic fibrosing pulmonary aspergillosis, lifelong use of antifungal drugs is usual. Itraconazole and voriconazole are first and second-line anti fungal agents respectively. Posaconazole can be used as third-line agent, for patients who are intolerant of or developed resistance to the first and second-line agents. Regular chest X-rays, serological and mycological parameters as well as quality of life questionnaires are used to monitor treatment progress. It is important to monitor the blood levels of antifungals to ensure optimal dosing as individuals vary in their absorption levels of these drugs.

According to the International Labour Office (ILO), PMF requires the presence of large opacity exceeding 1 cm (by x-ray). By pathology standards, the lesion in histologic section must exceed 2 cm to meet the definition of PMF. In PMF, lesions most commonly occupy the upper lung zone, and are usually bilateral. The development of PMF is usually associated with a restrictive ventilatory defect on pulmonary function testing. PMF can be mistaken for bronchogenic carcinoma and vice versa. PMF lesions tend to grow very slowly, so any rapid changes in size, or development of cavitation, should prompt a search for either alternative cause or secondary disease.

A1AT deficiency remains undiagnosed in many patients. Patients are usually labeled as having COPD without an underlying cause. It is estimated that about 1% of all COPD patients actually have an A1AT deficiency. Thus, testing should be performed for all patients with COPD, asthma with irreversible airflow obstruction, unexplained liver disease, or necrotizing panniculitis. The initial test performed is serum A1AT level. A low level of A1AT confirms the diagnosis and further assessment with A1AT protein phenotyping and A1AT genotyping should be carried out subsequently. The Alpha-1 Foundation offers free, confidential testing.

As protein electrophoresis does not completely distinguish between A1AT and other minor proteins at the alpha-1 position (agarose gel), antitrypsin can be more directly and specifically measured using a nephelometric or immunoturbidimetric method. Thus, protein electrophoresis is useful for screening and identifying individuals likely to have a deficiency. A1AT is further analyzed by isoelectric focusing (IEF) in the pH range 4.5-5.5, where the protein migrates in a gel according to its isoelectric point or charge in a pH gradient.

Normal A1AT is termed M, as it migrates toward the center of such an IEF gel. Other variants are less functional and are termed A-L and N-Z, dependent on whether they run proximal or distal to the M band. The presence of deviant bands on IEF can signify the presence of alpha-1 antitrypsin deficiency. Since the number of identified mutations has exceeded the number of letters in the alphabet, subscripts have been added to most recent discoveries in this area, as in the Pittsburgh mutation described above. As every person has two copies of the A1AT gene, a heterozygote with two different copies of the gene may have two different bands showing on electrofocusing, although a heterozygote with one null mutant that abolishes expression of the gene will only show one band. In blood test results, the IEF results are notated as, e.g., PiMM, where Pi stands for protease inhibitor and "MM" is the banding pattern of that person.

Other detection methods include use of enzyme-linked-immuno-sorbent-assays in vitro and radial immunodiffusion.

Alpha 1-antitrypsin levels in the blood depend on the genotype. Some mutant forms fail to fold properly and are, thus, targeted for destruction in the proteasome, whereas others have a tendency to polymerize, thereafter being retained in the endoplasmic reticulum. The serum levels of some of the common genotypes are:

- PiMM: 100% (normal)

- PiMS: 80% of normal serum level of A1AT

- PiSS: 60% of normal serum level of A1AT

- PiMZ: 60% of normal serum level of A1AT

- PiSZ: 40% of normal serum level of A1AT

- PiZZ: 10-15% (severe alpha-1 antitrypsin deficiency)

Progressive Massive Fibrosis (PMF), characterized by the development of large conglomerate masses of dense fibrosis (usually in the upper lung zones), can complicate silicosis and coal worker's pneumoconiosis. Conglomerate masses may also occur in other pneumoconioses, such as talcosis, berylliosis (CBD), kaolin pneumoconiosis, and pneumoconiosis from carbon compounds, such as carbon black, graphite, and oil shale. Conglomerate masses can also develop in sarcoidosis, but usually near the hilae and with surrounding paracitricial emphysema.

The disease arises firstly through the deposition of silica or coal dust (or other dust) within the lung, and then through the body's immunological reactions to the dust.