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Tests During An Asthma Attack

Reviewed by: HU Medical Review Board | Last reviewed: June 2023

During an asthma attack, symptoms worsen quickly. Asthma attacks can happen whether or not you have been diagnosed with asthma. Some asthma attacks can be managed at home. More severe asthma attacks may need emergency attention. Your asthma action plan will help you respond during an asthma attack.1

Tests can help doctors diagnose, assess, and treat an asthma attack. Common tests for asthma – such as bloodwork, peak flow, chest X-ray, and spirometry – assess lung function. Doctors may perform some of these tests while starting quick-relief treatments. At-home tests can also help you respond during an asthma attack.2

Why are tests done during an asthma attack?

Doctors will perform tests during an asthma attack in a doctor’s office or emergency room. They may do this to:1,3

  • Confirm a diagnosis of an asthma attack
  • Understand the severity of the asthma attack
  • Check if you are in or near respiratory failure
  • See how well quick-relief treatments are working
  • Rule out other conditions or complications

This information will help your doctor decide on the best treatment during an asthma attack. It can also help them adjust treatments after an asthma attack.3,4

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You may also perform tests when an asthma attack starts at home. The results may help you respond to signs of an asthma attack. Your asthma action plan will tell you what to do based on test results.2

What symptoms do doctors use to assess an asthma attack?

While starting treatment, doctors will assess your symptoms. This can help determine the severity of the asthma attack. Some signs of a severe asthma attack include:3,5

  • Rapid breathing
  • Rapid heartbeat
  • Sweating
  • Difficulty speaking in full sentences or phrases
  • Difficulty lying down
  • Severe drop in blood pressure while breathing in

Doctors will monitor you for signs of impending respiratory failure. Respiratory failure is when the lungs do not get enough oxygen into the blood. Respiratory failure can be life-threatening and needs emergency treatment in a hospital. Signs of respiratory failure include:3,6

  • Drowsiness
  • Confusion
  • Absence of wheezing sounds
  • Slower heart rate
  • Bluish color on fingers, toes, and lips

Doctors will monitor you for signs of other conditions. For example, fever or hives may indicate pneumonia or another diagnosis. These signs can help doctors make the correct diagnosis during an asthma attack.3

What types of tests are used to assess an asthma attack?

Sometimes, severe asthma attacks do not show typical symptoms. Test results are more reliable to diagnose and assess asthma attacks. Doctors will perform these tests while starting treatment. Some common tests during an asthma attack include:3

Peak flow

Peak flow measures how fast you can breathe out. You may use a peak flow meter at home to monitor lung function. Doctors may take peak flow readings while treating your asthma attack. Peak flow is a reliable way to assess the severity of an asthma attack.1-3

The test is done by blowing into a mouthpiece as hard as possible in a single breath. The result of a peak flow test is called your “peak expiratory flow” (PEF). Normal PEF values are different for everyone. Your asthma action plan will help you determine what your PEF results mean.1,3


Spirometry measures how much air you can breathe out. During the test, you take deep breaths and breathe out into a spirometer. The result of a spirometry test is “forced expiratory volume” (FEV). Your FEV can help doctors evaluate your lung function.1,2

Typically, spirometry is used to assess baseline asthma or mild asthma attacks that don’t require emergency room treatment. Spirometry is a simple and common way to diagnose or assess asthma.1,2

Pulse oximetry

Pulse oximetry measures the amount of oxygen in your blood (called "oxygen saturation"). A pulse oximeter is a small clip placed on your finger, toe, forehead, or earlobe. It is used to assess asthma attacks when lung function tests are not possible. For example, a doctor may use pulse oximetry for adults with signs of respiratory failure or young children.1-3

Oxygen saturation may still be normal during an asthma attack. But a low oxygen saturation may be a sign of respiratory failure.1,3

Arterial blood gas (ABG)

Blood tests can measure the amount of oxygen and carbon dioxide in your blood. Increased levels of carbon dioxide may indicate respiratory failure. Doctors will use a blood sample from your wrist for the test.3

ABG measurements are usually only needed if you are sick enough to need treatment in the emergency room.3

Chest X-rays

Chest X-rays are commonly used to make sure you do not have another condition, such as a collapsed lung or pneumonia. They cannot diagnose an allergy attack but can rule out these other conditions.3