Diagnosing patients with 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.
Why are ILDs often missed?
The gradual onset and slow progression of ILD symptoms can make early diagnosis challenging. Common symptoms such as breathlessness, persistent cough and fatigue are often non specific and may be mistaken for more common conditions such as asthma or COPD, or attributed to ageing or physical deconditioning. This overlap can make it difficult to recognise ILD, particularly in older adults who may already have multiple comorbidities.
See here for the national and international best practice guidelines for ILD.
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? |
Dry, persistent cough: usually non-productive and not relieved by prescription or over the counter/home remedies. Fatigue: often one of the most significant symptoms in ILD and can have a major impact on quality of life, social interactions, and work. Joint aches, swelling or pains: along with fatigue, this might suggest connective tissue disease, which can be associated with ILDs. Ensure that red flag symptoms such as chest pain, leg swelling, palpitations, haemoptysis and weight loss are recorded and investigated appropriately. |
|
How are these symptoms affecting your life? Have they stopped you doing any of your usual activities? |
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 treatments have you tried for your breathing symptoms, and have they helped? |
ILDs are often initially mistaken for more common respiratory conditions, such as asthma or COPD. As a result, patients may be prescribed treatments such as inhaled corticosteroids, bronchodilators or oral corticosteroids without significant improvement in their symptoms. If a patient is not responding to treatment as expected, despite good adherence and inhaler technique, it is important to review the diagnosis and consider alternative causes of their symptoms, including ILD. |
|
Have you got any medical conditions, past or current? Has anyone in your family has ILD? What medications have you taken in the past? Have you ever had radiation therapy? |
Auto immune conditions, connective tissue disorders, sarcoidosis, gastroesophageal reflux disease, COVID infection, lupus, 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 are associated with drug-induced ILD. These include some chemotherapy agents, disease modifying anti-rheumatic drugs (DMARDs), antiarrhythmic medications such as amiodarone, and antibiotics such as nitrofurantoin. When assessing a patient with suspected ILD, it is important to take a detailed medication history, including current and previous treatments, as drug-induced ILD may improve if the causative medication is identified and discontinued. 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, and the working lives of the people you live with. |
Make sure that you include the entirely of your patient's career so that you capture any high risk occupations or exposures. Remember that families or housemates 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.
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 fine bilateral inspiratory crackles, often described as sounding like the separation of Velcro. These crackles are usually heard at the lung bases and are caused by the sudden opening of collapsed small airways and airspaces during inspiration as a result of fibrosis or inflammation.
The presence of persistent, unexplained inspiratory crackles should raise suspicion of ILD and prompt further investigation.
Finger clubbing
Finger clubbing is a physical sign that can occur in some people with ILD, particularly those with pulmonary fibrosis. It causes the fingertips to become enlarged and the nails to curve more than usual. The exact cause is not fully understood, but it is thought to result from changes in blood flow and the release of growth factors that stimulate tissue growth in the fingers. While finger clubbing is associated with chronic lung disease, it is not caused solely by low oxygen levels. The presence of finger clubbing should raise suspicion of an underlying lung condition and prompt further assessment.
To assess for finger clubbing, ask the patient to place the nails of their index fingers back to back. In normal fingers, a small diamond shaped gap between the nail beds, known as Schamroth’s window, should be visible. In patients with finger clubbing, this gap is reduced or absent.
Spirometry
In ILD, spirometry may show a restrictive pattern because scarring and inflammation make the lungs stiffer and reduce their ability to expand fully. As a result, lung volumes are reduced and patients are unable to inhale as much air as normal.
This leads to a reduction in vital capacity (VC) and forced vital capacity (FVC). Forced expiratory volume in one second (FEV₁) is also usually reduced, but proportionately to FVC. As a result, the FEV₁/FVC ratio is typically normal or increased. If the patient has coexisting airflow obstruction, such as asthma or COPD, the FEV₁/FVC ratio may be reduced.
A restrictive pattern cannot be confirmed by spirometry alone. Patients usually require full pulmonary function tests, including lung volume and gas transfer measurements, to confirm and assess the severity of lung disease.
Oxygen saturation
Oxygen saturation may be reduced in ILD because fibrosis and inflammation can impair gas exchange, making it harder for oxygen to pass from the alveoli into the bloodstream.
Oxygen saturations should be measured both at rest and during exertion. Exertional desaturation is a common feature of ILD and may occur before resting hypoxaemia develops. This happens because the damaged lung tissue is less able to transfer oxygen into the blood when oxygen demand increases during activity.
Resting oxygen saturations of 92% or below, or significant desaturation during exercise, should prompt specialist respiratory 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. A normal chest x-ray does not exclude ILD.
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, such as high resolution computed tomography (HRCT)
- Functional testing, including pulmonary function tests and exercise testing
- Invasive procedures, such as bronchoscopy or lung biopsy, where appropriate
These investigations help build a detailed picture of the lung disease, including its type, severity and possible underlying cause. The results are usually reviewed by a multidisciplinary team (MDT), which may include respiratory physicians, radiologists, pathologists, specialist nurses and other healthcare professionals with expertise in ILD. The MDT uses this information to reach a diagnosis and develop an appropriate management plan, which is then discussed with the patient.
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.