Are lung function tests used to diagnose pulmonary fibrosis? 

Lung function tests, also known as pulmonary function tests, are essential tools used by respiratory specialists in the United Kingdom to evaluate the health and efficiency of the respiratory system. When a patient presents with symptoms such as a persistent cough or increasing breathlessness, these tests provide objective data that helps clinicians understand how the lungs are performing. While they are a vital component of the diagnostic process, they are typically used alongside imaging and clinical history to form a complete picture of a patient’s health. In the UK, the NHS provides these tests in hospital settings to ensure that any abnormalities in lung capacity or oxygen transfer are identified early and managed appropriately according to national standards. 

What We’ll Discuss in This Article 

• The role of lung function tests in identifying respiratory abnormalities. 

• How spirometry helps identify restrictive patterns in the lungs. 

• The significance of gas transfer tests in evaluating oxygen uptake. 

• Why breathing tests are used to monitor disease stability over time. 

• The collaborative role of these tests in a multidisciplinary diagnosis. 

• What patients can expect during a typical lung function assessment. 

What are lung function tests? 

Lung function tests are a series of non-invasive breathing assessments used by UK healthcare professionals to measure various aspects of respiratory performance. These tests do not involve any needles or internal cameras, but instead require the patient to blow into a machine through a mouthpiece. Lung function tests are used to check how well your lungs are working and to help diagnose lung conditions such as pulmonary fibrosis. The results provide specific measurements regarding the volume of air the lungs can hold, the speed at which air can be expelled, and the efficiency with which oxygen passes from the lungs into the bloodstream. By comparing these results to a set of predicted values based on a person’s age, height, and gender, specialists can determine if the lungs are functioning within a normal range. 

Spirometry and the restrictive pattern 

Spirometry is the most common lung function test and is often the first breathing assessment a patient will undergo. It involves taking a deep breath and then blowing out as hard and as fast as possible into a device called a spirometer. In many lung conditions, such as asthma or COPD, the primary issue is an obstruction in the airways. However, in pulmonary fibrosis, the issue is that the lungs have become stiff and scarred, which reduces their total capacity. NICE guidance for diagnosing pulmonary fibrosis indicates that spirometry typically shows a restrictive pattern of lung disease. This restrictive pattern means that while the person can blow air out quickly, the total amount of air they can hold is significantly lower than expected. This stiffness is a direct result of the scar tissue replacing healthy, elastic lung tissue. 

Measuring oxygen transfer with the DLCO test 

The gas transfer test, often referred to as the DLCO (diffusing capacity of the lungs for carbon monoxide), is a more specialised assessment that is particularly important for patients with suspected lung scarring. This test measures how easily a tiny, harmless amount of tracer gas passes from the air sacs into the blood. Because pulmonary fibrosis causes the walls of the air sacs to thicken and scar, the journey of oxygen into the bloodstream becomes much more difficult. A reduction in the gas transfer measurement is often one of the earliest signs of interstitial lung disease detected during clinical testing. If this value is low, it indicates that the barrier between the air and the blood is becoming a physical obstacle to efficient respiration, which explains why patients feel breathless even when taking deep breaths. 

Lung volume measurements and plethysmography 

To get a complete understanding of how much the lungs have been affected by scarring, specialists may perform a test called body plethysmography. This involves sitting inside a clear, airtight booth that looks similar to a telephone box. By measuring the changes in pressure within the booth as the patient breathes, the machine can calculate the total volume of air in the lungs, including the air that remains after a full exhalation. This is known as the Total Lung Capacity (TLC). In pulmonary fibrosis, all lung volumes are typically reduced because the tough scar tissue prevents the lungs from expanding to their full size. This objective measurement of “small lungs” is a key indicator used by the multidisciplinary team to confirm a diagnosis of a restrictive lung condition. 

Monitoring disease stability and treatment 

Once a diagnosis has been established, lung function tests remain a cornerstone of patient care in the UK. They are not only used for the initial diagnosis but are also the primary method for tracking how the disease is behaving over months and years. Patients are usually invited back to the hospital every three to six months to repeat these tests. By comparing the new results with previous ones, the respiratory team can see if the lung function is remaining stable or if it is starting to decline. This data is essential for making clinical decisions, such as when to start antifibrotic medications or when to refer a patient for a lung transplant assessment. Regular monitoring ensures that any changes are caught early and that the treatment plan is adjusted to provide the best possible support for the patient’s respiratory health. 

The role of breathing tests in the diagnostic journey 

It is important to understand that lung function tests are rarely used in isolation to provide a definitive diagnosis of pulmonary fibrosis. Instead, they act as a piece of a larger puzzle. A specialist will look at the breathing test results alongside a detailed medical history, physical examination findings, and high-resolution CT scans. For example, a restrictive pattern on a spirometry test combined with “velcro-like” crackles heard through a stethoscope and specific scarring patterns on a scan would lead to a confident diagnosis. In the UK, this evidence is reviewed by a multidisciplinary team (MDT), which includes doctors, nurses, and radiologists, to ensure that the diagnosis is accurate and that no other conditions are causing the symptoms. 

Conclusion 

Lung function tests are indispensable tools in the UK for the identification and ongoing management of pulmonary fibrosis. By measuring the physical capacity of the lungs and the efficiency of oxygen transfer, these tests provide a clear window into how lung scarring is affecting a person’s health. While the tests themselves are non-invasive and safe, the information they provide is vital for ensuring that patients receive timely and accurate care within the NHS. If you experience severe, sudden, or worsening symptoms, call 999 immediately. 

Authority Snapshot (E-E-A-T Block) 

This article provides an overview of the role of lung function tests in the diagnosis of pulmonary fibrosis, ensuring all information is consistent with the standards of the NHS and NICE. The goal is to provide a clear and reliable explanation for the UK public regarding the clinical procedures used in respiratory medicine. This content was produced by a medical content team and reviewed by Dr. Rebecca Fernandez, a UK-trained physician, to ensure clinical accuracy and balance.