Oncologists use various imaging tests and tissue sample biopsies to definitively diagnose lung cancer. After diagnosis, health care teams may order pulmonary function tests (PFTs, or lung function tests) to analyze breathing patterns and help direct treatment or make surgical decisions. Although these breath tests can’t currently be used to diagnose lung cancer, ongoing clinical trials are researching how other breath tests could detect certain molecules in the breath (called volatile organic compounds or VOCs) that could indicate lung cancer at an early stage.

Here is what you need to know about the different types of lung cancer breath tests used today, as well as new methods of detection being developed and tested.

Current Breath Tests for Lung Cancer

When a person is first diagnosed with lung cancer, the pulmonologist (a doctor who specializes in the lungs) may want to conduct a pulmonary function test, also known as a breath test. The test result help can guide the pulmonologist to find the right treatment. The two standard breath tests are spirometry and plethysmography.

Body Plethysmography

Initially, people diagnosed with lung cancer may undergo a test known as body plethysmography. During body plethysmography, you’ll sit in an enclosed clear chamber (if you feel claustrophobic, let your technician know, and they can accommodate). Inside the chamber, you’ll be asked to breathe into a mouthpiece while wearing nose clips. For around 15 minutes, the technician will lead you through different breaths, from long, deep breaths to short, quick breaths.

During the test, the air inside the box will begin to reflect the pressure and volume of each breath. The device is not only measuring the direct feedback from breathing into the mouthpiece — it is also taking into account the shifts in the air around you.

The technician will compare your results in lung capacity and airflow resistance to those of average healthy lungs. Lung surgery for cancer by necessity removes some healthy lung tissue, and not enough may be left to allow normal breathing. Plethysmography results can help your health care team determine the safest treatment moving forward — for instance, if your lungs likely couldn’t handle the stress of surgery, then your pulmonologist may recommend chemotherapy or radiation therapy instead.

Spirometry

Throughout your lung cancer treatment, your pulmonologist may ask you to take routine spirometry tests. A spirometry test assesses how much you inhale and exhale and how quickly. The test results can help your doctors evaluate how well your treatment is working.

For this test, you will be seated in front of a measurement machine called a spirometer and given a nose clip to wear while you breathe into the machine’s mouthpiece. Your technician will ask you to take a deep breath, and when you next exhale, force all the air out of your lungs into the mouthpiece.

This test will allow your pulmonologist to collect data on your forced vital capacity and forced expiratory volume — factors that essentially measure the force and practical strength of your lungs.

Preparing for a Breath Test

There are a few things to keep in mind while preparing for a PFT. On the day of the test, make sure you haven’t taken any medicine to regulate your breathing unless advised to by your doctor. If you smoke, do not smoke before the test. You may also want to avoid eating a large meal before the test.

What Are the Risks?

Breath tests are noninvasive, so there is very little risk involved. However, as you go through rapid breathing cycles, it’s common to experience lightheadedness and shortness of breath. If the tests are proving to be difficult, you may also cough. If this happens, ask your technician for some time to rest.

It’s also important to be mindful of some risk factors that might interfere with these breathing tests. For example, if you’ve recently undergone surgery or have heart problems, talk to your pulmonologist for their signoff before beginning the test.

The Future of Breath Tests for Lung Cancer

A reliable method of early diagnosis for lung cancer has been slow to materialize. Only 16 percent of all cases of lung cancer are diagnosed early on in the disease. This low rate of early-stage lung cancer detection is partly because symptoms of lung cancer often do not appear until the cancer has metastasized (spread to other areas of the body) and reached an advanced stage. There are guidelines for early screening, but it is restricted to only high-risk individuals because the screening carries risks of its own, including false-positive results.

The good news is that the current outlook for breath collection devices as screening and diagnostic tools is becoming more and more promising. For example, the makers of one breath biopsy device are currently recruiting healthy volunteers to conduct clinical trials. If their breathing test gains FDA approval, it may be possible to receive such screening in the future.

Research on Breath Tests’ Diagnostic Accuracy

A trailblazing 1985 study first identified the VOCs that lung cancer manifests in exhaled breath. However, the sample size was relatively small, with only 12 people with late-stage lung cancer and 17 people in the healthy control group.

In a 2015 study, researchers examined many more breath samples across various trials. Through a process known as gas chromatography, the researchers were able to isolate and classify lung cancer-specific VOCs. The researchers found nearly 1,000 specific particles that could potentially verify and support a lung cancer diagnosis.

Dogs can also detect lung cancer from a person’s breath. One study found that a trained dog had a very high rate of accuracy in distinguishing between the breath of people with and without lung cancer. This finding was very important in the field of breath testing for lung cancer.

Comparing CT Scans to Breath Analysis

As the researchers of the 2015 study concluded, a breath biopsy should not be used alone to diagnose lung cancer. It may act as a supplemental diagnostic tool to support the findings of a computerized tomography (CT) scan. The researchers found that combining a CT scan with a breath biopsy significantly reduced the false-positive diagnosis rate.

The objective of a low-dosage computerized tomography (LDCT) scan — the scan used for early lung cancer screening in some people — is to detect growths in the lungs, called pulmonary nodules. Although an LDCT allows oncologists to detect these nodules, a scan alone cannot categorize them as either benign (noncancerous) or malignant (cancerous).

But another study, in which researchers conducted breath analysis on people with pulmonary nodules, showed that the breath testing could distinguish between benign and malignant nodules. The breath tests were also able to determine the stage of cancer as well as the type of non-small cell lung cancer.

In a more recent 2019 validation study, researchers concluded that breath-based biomarkers might provide a more definitive diagnosis than a traditional LDCT scan. However, more research is needed.

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Have you undergone breathing tests for lung cancer? What do you think about the future of breathing tests, and would you ever take part in a clinical trial? Share your thoughts in the comments below or by posting on MyLungCancerTeam.