Oxygen therapy is a medical treatment that helps people whose bodies cannot get enough oxygen on their own. Whether you need oxygen all the time or just during certain activities, understanding when and how this therapy works can make a real difference in managing your health and maintaining your quality of life.

Who Should Undergo Diagnostics and When

If you find yourself struggling to breathe, feeling unusually tired, or experiencing confusion alongside breathing difficulties, it may be time to talk to your healthcare provider about oxygen testing. These symptoms can signal that your body isn’t getting the oxygen it needs to function properly. However, not everyone who needs supplemental oxygen will notice obvious warning signs, which is why testing becomes especially important.

People living with certain lung conditions are the most common candidates for oxygen therapy evaluation. If you have been diagnosed with chronic obstructive pulmonary disease (COPD)—a long-term lung condition that makes breathing difficult—your doctor will regularly monitor your oxygen levels. The same applies if you’re dealing with pulmonary fibrosis, a condition where the tissue deep inside your lungs becomes scarred and stiff, making it harder for oxygen to pass into your bloodstream.^[1]

Other conditions that often require oxygen level monitoring include pneumonia, asthma, cystic fibrosis, heart failure, sleep apnea, and lung cancer. Even people recovering from COVID-19 sometimes need oxygen therapy temporarily while their lungs heal. Beyond illness, people who live at high altitudes or plan to climb mountains may also need their oxygen levels checked, as the air contains less oxygen the higher you go.^[1]

You don’t always need to wait for severe symptoms before seeking oxygen diagnostics. Many healthcare providers routinely check oxygen levels during regular appointments, especially if you have a lung or heart condition. Some people experience shortness of breath during physical activity, rapid heartbeat when moving around, or swelling in their ankles—all possible signs that oxygen isn’t reaching your tissues as it should. Others may notice a bluish color on their fingertips or lips, which happens when oxygen levels drop too low.^[5]

What makes oxygen diagnostics particularly important is that some individuals don’t experience any symptoms even when their oxygen levels are dangerously low. Your body might be quietly struggling without giving you clear warning signals. This is why regular testing matters, especially for anyone with chronic lung or heart disease.^[14]

Diagnostic Methods Used to Identify the Need for Oxygen Therapy

When your healthcare provider wants to find out if you need supplemental oxygen, they will use specific tests to measure how much oxygen is actually in your blood. These tests are straightforward but provide critical information about whether your cells are receiving what they need to function.

Pulse Oximetry

The most common and easiest test is called pulse oximetry. This involves a small device that clips painlessly onto your finger, toe, or earlobe. The device, called a pulse oximeter, shines light beams through your skin to measure oxygen levels in the tiny blood vessels called capillaries. The test takes just seconds and doesn’t require any needles or blood samples.^[1]

Many doctors perform this test routinely at every appointment, especially for patients with lung or heart conditions. You can even purchase a pulse oximeter at most drugstores to monitor your levels at home if your doctor recommends it. The device provides a reading called oxygen saturation, which is the percentage of oxygen carried by your red blood cells. This is often abbreviated as O2 sat.^[1]

A healthy oxygen saturation level is typically between 95% and 100%. When levels drop below 88%, healthcare providers often prescribe oxygen therapy. The pulse oximeter gives a quick estimate, but it doesn’t provide as much detailed information as blood testing. It can also be affected by factors like cold hands, nail polish, or certain medical conditions that affect blood flow.^[1]

Arterial Blood Gas Test

For the most accurate measurement of oxygen levels, doctors use an arterial blood gas (ABG) test. This test requires drawing a small blood sample from an artery, usually in your wrist. Unlike regular blood tests that use veins, this test measures oxygen directly from the blood that has just left your lungs and is carrying oxygen to your body.^[1]

The ABG test measures not only oxygen levels but also carbon dioxide levels in your blood, which helps your doctor understand how well your lungs are working overall. Normal arterial blood oxygen levels range between 75 and 100 millimeters of mercury (mmHg). If your level drops to 60 mmHg or lower, you likely need supplemental oxygen. The test can be done in a doctor’s office, clinic, or hospital wherever the proper equipment is available.^[4]

While the ABG test involves a needle stick and may cause brief discomfort, it provides crucial information that a pulse oximeter cannot capture. Your healthcare provider will decide which test—or combination of tests—is most appropriate for your situation.

Pulmonary Function Tests

Beyond measuring oxygen in your blood, doctors sometimes use pulmonary function tests to understand how well your lungs are working. One common test is called spirometry, which measures how much air you can breathe in and out, and how quickly you can exhale. These tests help doctors see whether your lungs can move enough air and whether they’re able to transfer oxygen into your bloodstream effectively.^[1]

During spirometry, you breathe into a mouthpiece connected to a machine. The test is painless and typically takes just a few minutes. The results give your healthcare team a clearer picture of your lung capacity and function, which helps them decide if oxygen therapy would benefit you and how much oxygen you might need.

Monitoring During Activity and Sleep

Sometimes your oxygen levels are fine when you’re sitting quietly but drop significantly during physical activity or while you sleep. To capture this, your doctor may ask you to wear a pulse oximeter during a walking test or overnight. This helps identify situations when you might need supplemental oxygen even if your resting levels seem normal.^[5]

For instance, people with pulmonary fibrosis often experience lower oxygen levels when moving around, even if their levels are adequate at rest. Similarly, individuals with sleep apnea may have normal daytime oxygen but dangerous drops during the night. Portable monitoring devices allow doctors to see these patterns and prescribe oxygen for specific times or activities.^[1]

Diagnostics for Clinical Trial Qualification

Clinical trials studying new treatments for lung diseases, heart conditions, or other illnesses often have specific requirements for oxygen levels before someone can participate. These criteria help researchers ensure the study includes patients who might benefit from the treatment being tested and that the results can be accurately measured.

When evaluating potential participants, researchers typically use the same diagnostic tools described earlier: pulse oximetry and arterial blood gas testing. However, the specific oxygen level thresholds for enrollment vary depending on the trial’s goals. Some studies may only include patients whose oxygen saturation falls below a certain percentage, while others might require that participants need oxygen therapy during specific activities like walking or sleeping.^[3]

Beyond simple oxygen measurements, clinical trials often require more comprehensive lung function testing. Spirometry results showing how much air you can move in and out of your lungs help researchers understand the severity of your condition and whether you fit the study’s patient profile. Some trials also measure how far you can walk in six minutes, tracking your oxygen levels throughout the test to see how physical activity affects your breathing.^[3]

Researchers may also monitor how your oxygen levels respond to different flow rates or delivery methods. This helps them understand your oxygen needs more precisely and ensures the trial protocol will work for you. In some cases, you might need to keep a log of your oxygen use at home, recording when you use it, at what flow rate, and during which activities.

If you’re interested in participating in a clinical trial related to conditions requiring oxygen therapy, your healthcare provider will perform all necessary diagnostic tests to determine if you meet the study’s criteria. These tests not only help with trial enrollment but also provide valuable information about your condition that can guide your overall treatment plan.