01Purpose and principlesWhat the assessment is for and the core concepts behind it.
Interstitial lung diseases are diverse disorders affecting alveoli, interstitium, small airways and pulmonary vessels in different proportions. A useful first division is known association versus idiopathic disease: connective-tissue disease, exposure, medicine, radiation and occupational dust may provide the cause, while an idiopathic interstitial pneumonia is diagnosed only after credible alternatives have been addressed. The clinical aim is not merely to label an HRCT image, but to find a diagnosis that explains the person, predicts behaviour and changes management.
Work in parallel rather than serially. Define tempo and severity, assemble a lifetime exposure and medicine timeline, examine for extrapulmonary clues, measure physiology and obtain protocolled HRCT. The respiratory physician, thoracic radiologist, specialist nurse and, where needed, pathologist or rheumatologist combine these strands at multidisciplinary discussion. Bronchoscopy or biopsy is justified only if the result is likely to alter a decision and procedural risk is acceptable.
The phrase progressive pulmonary fibrosis describes behaviour across several fibrotic ILDs rather than one cause. Worsening symptoms, physiological decline and radiological progression must be interpreted together after excluding infection, cardiac disease, poor test quality and other explanations. Antifibrotic eligibility is a specialist commissioning decision; inflammatory disease may instead require exposure removal or immunomodulation.
Key points
- ILD is an umbrella description, not a final diagnosis: classify the clinical context, HRCT pattern and likely cause before selecting treatment.
- Take an exposure history that reaches beyond occupation to birds, mould, hot tubs, humidifiers, hobbies, dusts, vaping, radiotherapy and every prescribed or non-prescribed medicine.
- Search actively for connective-tissue disease through Raynaud phenomenon, inflammatory joints, rashes, proximal weakness, sicca symptoms, dysphagia and mechanic's hands.
- A normal chest radiograph does not exclude early ILD; persistent compatible symptoms or basal crackles justify spirometry, gas transfer and specialist imaging consideration.
- HRCT pattern language guides probability but does not replace context: usual interstitial pneumonia can occur in IPF, connective-tissue disease, chronic hypersensitivity pneumonitis and asbestosis.
- Serial forced vital capacity, gas transfer, symptoms and exertional oxygenation reveal trajectory more reliably than a single measurement.
- Clubbing and fine late-inspiratory basal crackles support fibrotic lung disease, but their absence does not safely rule it out.
- Diagnosis should be reviewed in an ILD multidisciplinary meeting when clinical, radiological or pathological evidence is uncertain or treatment carries material risk.
- Acute deterioration is a syndrome requiring a fresh differential; infection, pulmonary embolism, cardiac failure and treatment toxicity are often more actionable than acute exacerbation.
- Management includes diagnosis-specific therapy, smoking cessation, vaccination, rehabilitation, oxygen assessment, symptom control, advance care planning and timely transplant discussion where appropriate.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
Months or years of exertional breathlessness and dry cough, fine basal inspiratory crackles, clubbing, restrictive physiology and reduced gas transfer suggest fibrotic ILD. Functional limitation may precede resting hypoxaemia.
Subacute cough, breathlessness, feverishness, weight loss or symptoms varying with home or work exposure raise hypersensitivity pneumonitis, organising pneumonia, drug reaction, sarcoidosis or connective-tissue disease.
Raynaud phenomenon, synovitis, skin tightening, photosensitive rash, proximal weakness, uveitis, erythema nodosum, neuropathy or renal abnormalities can redirect an apparently idiopathic lung presentation.
A rapid fall over days with new bilateral opacities, marked desaturation or increased work of breathing is an emergency. Consider infection, embolism, oedema, pneumothorax, haemorrhage, drug toxicity and acute exacerbation.
Disproportionate breathlessness, syncope, chest pain, raised jugular venous pressure, oedema or a gas-transfer reduction out of proportion to volumes warrants urgent evaluation for pulmonary vascular disease.
Haemoptysis, focal persistent opacity, unilateral effusion, pleural nodularity, unexplained weight loss or asymmetric lymphadenopathy should trigger the relevant urgent cancer pathway rather than being absorbed into an ILD label.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Structured history and examinationFirst step - Why
- Identify cause, tempo, comorbidity and immediate severity.
- Interpretation and limitations
- Record dates of symptoms, jobs and tasks, workplace controls, animals, damp, hobbies, medicines and radiotherapy. Ask targeted autoimmune questions and document crackles, clubbing, oxygenation, joints, skin and muscle strength.
- 02
Chest radiograph - Why
- Detect diffuse abnormality and important alternatives.
- Interpretation and limitations
- Reticulation, volume loss or bilateral opacities support diffuse lung disease, but sensitivity and specificity are limited. Effusion, lobar collapse, focal mass or pneumothorax changes urgency and pathway.
- 03
Full pulmonary function testing - Why
- Establish physiological impairment and a reproducible baseline.
- Interpretation and limitations
- Restriction and reduced TLCO are typical but obstruction, mixed defects or isolated low gas transfer occur. Interpret trends with effort, haemoglobin, emphysema and pulmonary vascular disease.
- 04
High-resolution computed tomography - Why
- Characterise distribution, dominant pattern and complications.
- Interpretation and limitations
- Evaluate reticulation, honeycombing, traction bronchiectasis, ground glass, consolidation, nodules, mosaic attenuation, air trapping, pleura and nodes. Expiratory or prone images are selected by the radiology protocol.
- 05
Autoimmune and cause-directed blood tests - Why
- Find a systemic association or competing diagnosis.
- Interpretation and limitations
- Choose serology from clinical features and local ILD pathways; an isolated low-titre antibody does not establish connective-tissue disease, while negative screening cannot exclude every inflammatory myopathy or evolving disorder.
- 06
Exercise oxygen assessment - Why
- Quantify exertional limitation and assess support needs.
- Interpretation and limitations
- A standardised walk test records distance, symptoms and desaturation. Results help rehabilitation and oxygen decisions but do not identify the ILD subtype.
- 07
Bronchoalveolar lavage or tissue sampling - Why
- Resolve selected uncertainty when the answer will change management.
- Interpretation and limitations
- Lavage may support infection, haemorrhage or an inflammatory differential but is rarely diagnostic alone. Cryobiopsy or surgical biopsy requires expert MDT selection because acute exacerbation and procedural harm are real risks.
04Clinical next stepsHow the result changes management or prompts escalation.
01First assessmentBuild the diagnostic matrixFirst stepPersistent breathlessness, cough, crackles or imaging suggests diffuse parenchymal lung disease.+
- 1Assess physiological stability and oxygenation first; arrange same-day care for acute hypoxaemia, haemodynamic compromise, haemoptysis or rapidly progressive symptoms.
- 2Construct symptom, medicine and lifetime exposure timelines, examine for connective-tissue and sarcoid features, then obtain chest imaging, full lung function and targeted blood tests.
- 3Refer to a specialist ILD service for protocolled HRCT interpretation and multidisciplinary integration; do not call a pattern 'idiopathic' before credible causes are examined.
- 4Agree whether further sampling would change treatment, record diagnostic confidence and uncertainty, and provide the patient with a named contact and safety-net.
02Acute changeTreat deterioration as a new problemSymptoms, oxygenation or imaging worsen over hours to weeks.+
- 1Stabilise using an ABCDE approach, prescribe oxygen to the relevant target, obtain blood gas when indicated and involve senior respiratory or critical-care clinicians early.
- 2Investigate infection, pulmonary embolism, heart failure, pneumothorax, acute coronary disease, aspiration, diffuse alveolar haemorrhage and medicine toxicity using presentation-specific tests.
- 3Discuss new bilateral ground-glass change with the ILD team; acute exacerbation remains a diagnosis of exclusion and empirical antimicrobial or immunosuppressive choices vary locally.
- 4Revisit treatment ceilings and the person's preferences while active reversible causes are managed; uncertainty should not delay supportive care.
03Longitudinal careTrack disease behaviour and burdenAn ILD diagnosis or working diagnosis has been established.+
- 1Set a baseline using symptoms, functional status, spirometry, TLCO and exertional oxygenation, then choose review frequency according to diagnosis, severity and recent trajectory.
- 2At review, compare symptoms and physiology, check adverse effects and adherence, reconsider exposure, and look for infection, reflux, sleep-disordered breathing, pulmonary hypertension and mood problems.
- 3Return progressive cases to MDT to revisit diagnosis and consider disease-specific immunomodulation, NICE-approved antifibrotic pathways, research studies or transplant referral.
- 4Offer rehabilitation, vaccination, smoking cessation, oxygen assessment, symptom support and advance care planning alongside pharmacological decisions.
05Procedure and medicine safetyRelevant preparation, treatment and contraindications.
Supplemental oxygen
In acute illness titrate to 94–98% for most adults or 88–92% when hypercapnic respiratory failure risk is present, pending blood gases and any individual target.Oxygen does not treat fibrosis or breathlessness without hypoxaemia. Ambulatory and long-term prescriptions require formal local assessment; changing requirement is a severity signal needing review.
Nintedanib for eligible progressive fibrosing ILD
Specialist initiation is usually 150 mg orally twice daily about twelve hours apart with food; 100 mg twice daily or interruption may be required for intolerance, following the current SmPC.Confirm the specific indication and specialist eligibility. Diarrhoea, nausea, liver injury, bleeding risk, arterial events, gastrointestinal perforation risk and pregnancy precautions require counselling and monitoring; interactions and hepatic impairment can alter use.
06Risks, monitoring and follow-upComplications, safety checks and further assessment.
- Record symptoms, exercise capacity, cough burden, weight and resting oxygen saturation at each planned review, comparing with the individual's baseline.
- Repeat spirometry and gas transfer at an interval set by diagnosis and activity, often three to six months during uncertain or progressive disease.
- Use a reproducible exertional test when function or oxygen needs change, documenting device, flow, distance and nadir saturation.
- Review medicine toxicity with regimen-specific blood tests and enquiry, including liver function for antifibrotics and infection or cytopenia surveillance for immunosuppression.
- Reassess diagnosis and complications if decline is discordant: consider HRCT, echocardiographic assessment, embolic disease, infection, emphysema or malignancy rather than assuming fibrosis alone.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Pattern is not aetiology
Usual interstitial pneumonia is a radiological or pathological pattern. IPF is one clinical diagnosis associated with it, but exposure and autoimmune causes must be considered.
Ask what the patient actually does
A job title can conceal cutting engineered stone, cleaning pigeon lofts or spraying isocyanates. Tasks, materials, ventilation and respiratory protection are more informative than occupation alone.
Normal volumes can mislead
Combined pulmonary fibrosis and emphysema may preserve spirometric volumes while gas transfer and exertional oxygenation are severely impaired.
Ground glass is nonspecific
It can represent inflammation, infection, oedema, haemorrhage, partial alveolar filling or fine fibrosis. Distribution, accompanying signs and clinical tempo determine meaning.
Diagnostic confidence can change
Exposure information, evolving systemic features or serial imaging may revise an MDT diagnosis. A documented working diagnosis should invite appropriate re-evaluation rather than create false certainty.
08Common pitfallsFrequent interpretation and management errors.
- 01
Starting corticosteroids for every bilateral ground-glass opacity before adequately excluding infection, oedema and drug toxicity.
- 02
Treating a radiology label as a complete diagnosis without exposure, medicine and autoimmune review.
- 03
Using a one-off forced vital capacity to reassure despite falling TLCO, desaturation or functional decline.
- 04
Ordering broad serology without clinical interpretation, then overcalling disease from an isolated antibody result.
- 05
Delaying palliative symptom support and advance care planning until all disease-modifying options are exhausted.
- 06
Proceeding to lung biopsy when the likely result would not alter management or procedural risk is disproportionate.