Investigations
1st investigations to order
chest x-ray
Test
The most important initial diagnostic test for OP.[48][49]
Chest x-ray is also of use in evaluating alternative diagnoses.[48][49]
Result
bilateral patchy infiltrates; waxing and waning opacities may develop over a couple of weeks; focal OP may present as a circular nodule in 1 lung or 3 to 5 nodules in both lungs
high-resolution chest CT scan (HRCT)
Test
HRCT is fundamental to establishing a diagnosis of OP and can be used to monitor the patient for treatment or response to treatment.[48][49]
The 'triangle sign' (the triangular ground glass opacity with the base on the pleura and the apex towards the mediastinum) is often distinctive for OP.[2]
Result
bilateral patchy ground glass opacities with air bronchograms usually located peripherally; focal OP may present as circular nodule in 1 lung or 3 to 5 nodules in both lungs; other radiographical patterns such as a diffuse infiltrative pattern, atoll sign, crazy paving, fibrotic changes and bands may be seen in OP
FBC
Test
Non-specific finding.
Result
WBC may be normal but often increased to 10,000-15,000/microlitre in cryptogenic OP
erythrocyte sedimentation rate
Test
Non-specific finding.
Result
elevated
Investigations to consider
CRP
Test
May help to exclude infection.
Result
raised in infection
sputum culture
Test
May help to exclude infection.
Result
may identify pathogen associated with infection
atypical viral screen
Test
May help to exclude infection.
Result
may identify virus associated with infection
pulmonary function tests
Test
In addition to the vital capacity and lungs volumes, obtaining the diffusing capacity is important to determine severity and monitor disease course.
Result
decreased vital capacity and diffusing capacity with no airflow obstruction
surgical lung biopsy
Test
Should be strongly considered especially in patients with an atypical presentation such as rapidly progressive disease, diffuse infiltrative disease, no known aetiology or associated disorder, an unusual chest CT pattern, or with moderately severe symptoms. Pathological criteria also state that the following features should not be present: extensive interstitial fibrosis, traction bronchiectasis, and histological honeycombing.[1][2]
A video-assisted thoracoscopy procedure is the preferred method for obtaining tissue.[28]
CT-guided transthoracic needle biopsy and transbronchial lung cryobiopsy are minimally invasive procedures that can be used as alternatives to surgical lung biopsy.[52][53][54] These may be important options in elderly or frail patients, as well as those with focal lesions. However, both procedures produce relatively small biopsy specimens that must be interpreted in the context of associated clinical and radiological findings.[53]
Result
organised polypoid granulation inflammatory tissue in the distal bronchial airways, respiratory bronchioles, alveolar ducts, and alveoli
creatine kinase
Test
This test should be obtained if there is no obvious cause, because OP may precede the diagnosis of connective tissue diseases by several months or years. Creatine kinase is useful for screening for polymyositis OP.
Result
usually negative; elevated if polymyositis is underlying cause
general autoimmune and myositis profile
Test
Should be performed to screen for connective tissue disease if there is no obvious cause for OP as it may precede the diagnosis of connective tissue diseases by several months or years. The profile should include testing for: antinuclear antibodies, rheumatoid factor, anti-Scl-70 antibodies, anti-Sjögren-syndrome-related antigen A antibodies, anti-Sjögren-syndrome-related antigen B antibodies, cyclic citrullinated peptide antibodies, anti-ribonucleoprotein antibodies, antisynthetase antibodies, anticardiolipin antibodies, lupus anticoagulant antibodies, anti-glomerular basement membrane antibodies, and antineutrophil cytoplasmic antibodies/myeloperoxidase antibodies/proteinase 3 antibodies.
Result
elevated antibodies if connective tissue disease is underlying cause
positron emission tomography (PET) scan
Test
May be useful in some patients thought to have focal nodular OP.
Result
typically low positive uptake on PET scan
bronchoscopy
Test
Bronchoscopic investigations, including analysis of bronchoalveolar lavage fluid, may be useful in some patients thought to have OP.
Result
may help to rule out other differential diagnoses such as eosinophilic pneumonia and to confirm that there is no active infection
Use of this content is subject to our disclaimer