Diagnosing interstitial lung disease
This section will help you to understand:
- How interstitial lung diseases (ILDs) are diagnosed, and
- Your role in supporting your patient in primary care through this process.
The diagnosis of ILDs usually takes place in secondary care and is often made by a multidisciplinary team. However, primary care is often where patients will first present with symptoms so it’s important that HCPs can spot the signs and symptoms of ILDs and know when to refer a patient.
ILDs are often overlooked in primary care. Up to 55% of ILD patients are initially misdiagnosed, leading to significant delays in treatment.
See here for the national and international best practice guidelines for ILD.
Delayed and misdiagnosis of ILDs
Reasons for delayed or misdiagnosis of ILDs
- Gradual onset and slow progression of symptoms
- Non-specific symptoms of breathlessness, persistent cough, and fatigue mistaken for:
- Asthma
- COPD
- General aging
- Physical deconditioning
This overlap makes it challenging for healthcare professionals to recognise ILD early on, particularly in older adults, who may already have multiple comorbidities.
History taking in ILD
If you suspect ILD may be the cause of your patient's symptoms, use the guide below to structure your patient assessment. You can also use this questionnaire.
| Questions to ask your patient | Why this question matters |
|---|---|
| What are your symptoms? |
Shortness of breath: typically remorseless in ILD and worsening over time, especially on exertion. Aches and pains: along with fatigue, this might suggest connective tissue disease, which can be associated wit ILDs Ensure that red flag symptoms such as chest pain, leg swelling, palpitations, haemoptysis and weight loss and recorded and investigated appropriately. |
| How are these symptoms affecting your life? |
Breathlessness from ILD may be restricting your patient's work, social life and other activities; they may be frightened by its progression. Continuous cough may be exhausting, and cause chest discomfort and urinary incontinence. It may be affecting sleep and confidence. |
| What medications are you currently taking and do they help? |
ILDs will often be unresponsive to treatments for more common respiratory conditions like asthma or COPD, such as inhaled or oral corticosteroids, or bronchodilators, despite good adherence and technique. This is because the large airways are generally unchanged in ILD; the alveoli (air sacs) is where the patient is affected. If your patient is not improving with their inhaled treatments for another condition, question the diagnosis. |
|
Have you got any medical conditions, past or current? Has anyone in your family has ILD? What medications have you taken in the past? |
Auto immune conditions, connective tissue disorders, sarcoidosis, gastroesophageal reflux disease, COVID infection, lupus, herpes, hepatitis C and Epstein Barr virus all increase the risk of ILD. ILDs can also coexist with asthma and COPD. Some ILDs are inherited. Certain medications, particularly chemotherapy drugs (e.g. cyclophosamide), DMARDs (Methotrexate) antiarrhythmic drugs (e.g. amiodarone), and antibiotics (e.g.nitrofurantoin), are known to cause drug-induced ILD. Radiation therapy is also associated with ILDs. |
| Are you a past or current smoker? What do you/have you smoked? |
Tobacco smoking significantly increases the risk of developing certain types of ILD. Record your patient pack years. Smoking or inhalation of Illicit drugs such as heroin, cannabis, methamphetamines or cocaine are associated with ILDs, as is inhalation of solvents such as glue, paint thinners and nitrites. |
| Tell me about your working life | Make sure that you include the entirely of your patient's career so that you capture any high risk occupations or exposures. Remember that partners of people in high risk occupations may also be exposed to substances if they handle contaminated clothing. |
| Tell me about your hobbies and your pets | High risk hobbies include having a small holding, horse keeping, home renovations (exposure to mould, asbestos etc) having a hot tub at home, going to nail salons, gardening, keeping birds as pets, playing woodwind instruments. |
| Tell me about your home life | Understand how your patient is coping at home, and if they are well supported. |
Physical examination and investigations
The following examination and investigations should be performed but must not delay referral to a respiratory specialist for diagnosis, for example if there is a delay in accessing spirometry.
Chest auscultation
You should only listen to your patient's chest if you are trained to do so. In a patient with ILD, you may hear bilateral inspiratory crackles, which sounds 'velcro like'. These sounds are caused by the opening of small airways and alveoli that have become collapsed due to the fibrosis or inflammation.
Finger clubbing
Finger clubbing is due to chronic low oxygen levels caused by the progressive scarring and fibrosis in the lungs. Oxygen deprived tissues, especially in the extremities like the fingers react by increasing blood flow, which leads to changes in the soft tissue around the nails, causing a club like appearance.
To test for finger clubbing, ask the patient to place the nails of their index fingers back-to-back and look at the space between them. In normal fingers, a small diamond-shaped gap, called Schamroth’s window is visible.
Spirometry
In ILD, you may see a restrictive spirometry pattern. This is because the volume of the lungs is reduced, and less air is breathed in.
Therefore, vital capacity and forced vital capacity will be reduced. The FEV1/FVC ratio will be either normal, unless the patient also has some obstruction in addition to restriction, in which case the ratio will be reduced.
| Patterns of spirometry | |
|---|---|
| Normal |
FEV1 and FVC above 80% predicted AND FEV1/FVC ratio above 0.7 or above Lower limit of normal (LLN) |
| Obstructive | FEV1/FVC ratio below 0.7 or LLN FEV1 generally reduced below 80% predicted The exemption is where Fev1 is over 80%, the ratio is below 0.7 or LLN, however there is scooping in the flow volume curve FVC normal (above 80% predicted) |
| Restrictive | FVC reduced below 80% predicted (however, Restrictive Lung Disease cannot be diagnosed on spirometry alone) FEV1 generally reduced below 80% FEV1/FVC ratio normal – above 0.7 or LLN |
| Mixed pattern | FEV1/FVC ratio below 0.7 or LLN FVC reduced below 80% predicted |
For more information, read this guide to performing and interpreting spirometry.
Oxygen saturation
O2 saturation will be reduced because the fibrosis or inflammation makes it harder for oxygen to pass from the alveoli into the blood. Ensure you measure O2 saturations whilst the patient is moving as well as at rest. Desaturation on movement is a key sign in ILD and occurs because the damaged alveoli can't meet the increased oxygen demand during activity. Saturations below 92% and a decrease during exercise of 4% or more is significant and should prompt referral for oxygen assessment.
Blood tests
You can request some or all of the following baseline bloods prior to referral to a respiratory specialist:
| Blood test | Rationale |
|---|---|
| Full blood count | To detect conditions like infections, anaemia, and eosinophilia |
| Autoimmune Screening Tests | To detect any underlying autoimmune conditions that could be causing ILD, |
| Serum Angiotensin-Converting Enzyme | ACE levels are used to help diagnose sarcoidosis. |
| C-Reactive Protein and Erythrocyte Sedimentation Rate | Elevated levels may indicate an inflammatory cause of ILD. |
| Liver Function Tests | Can be abnormal in systemic conditions like sarcoidosis or connective tissue diseases affecting multiple organs. |
| Urea and Electrolytes | To assess kidney function, especially important if ILD is suspected to be caused by systemic vasculitis or autoimmune disease. |
| B-type natriuretic peptide | To help diagnose and manage heart failure |
| Vitamin D and Calcium Levels | Hypercalcaemia and abnormal vitamin D metabolism are sometimes seen in sarcoidosis |
Chest x ray and/or high resolution CT scan
Fibrosis is not always evident on chest x-ray in early disease, but may have a hazy or patchy appearance.
HRCT provides detailed images of the lung parenchyma and can reveal patterns of fibrosis, inflammation, or ground-glass opacities, which are key for diagnosing the specific types of ILD and assess the extent of lung damage.
Further investigations in secondary care
In secondary care, the diagnosis and management of ILD may involve a combination of
- Further imaging
- Functional testing
- Invasive procedures
These investigations provide a comprehensive understanding of lung pathology, disease severity, and possible underlying causes, guiding the most appropriate treatment plan for each patient. The patient's results will be discussed by the multidisciplinary team and they will be given their diagnosis by a member of this team.
Supporting your patient
Awaiting a diagnosis is a stressful time. You can support your patient by signposting them to the A+LUK information pages, or to our Helpline where our respiratory specialist nurses can offer expert information on the diagnosis and treatment of ILDs.
The Helpline service is available to healthcare professionals, too. We can help you with advice about managing your patients’ care and we’re also here to lend you a caring ear when you need it.