One of the tricky things about asthma is that you can't always avoid your triggers. Pollution, pollen, mold, and other allergens are often in the air you breathe. And even if you don't feel the effects right away, these triggers may be doing their damage by irritating your airways. In other words, you may be headed for an asthma flare-up when you're not even expecting it.

Even if you're breathing OK, an asthma flare-up could be just around the corner. How can you tell? By using a tool called a peak flow meter. A peak flow meter is a portable device that you blow into like a balloon. It measures how well your lungs are working. If you have asthma, knowing how well your lungs are working will help you and your doctor control your asthma better.

If you can't blow out as much air as usual, it might mean that you'll have an asthma flare-up soon. How soon? It could be in the next hour or even 2 or 3 days away. But knowing this ahead of time can help you take steps to prevent a really bad flare-up.

Readings from the peak flow meter also can help your doctor check how well your asthma medicine is working. And they can help you figure out what's triggering your asthma symptoms if you take readings before and after you were exposed to a suspected trigger, such as animal dander.

How Do You Use It?

Using a peak flow meter is simple. Set it to zero. Then stand up, take a deep breath, hold it, and then blow as quickly and strongly into the device as you can. Record the number that the meter reads. Repeat this three times and use the highest recorded number as your reading.

That number alone isn't the whole story. You'll want to compare today's reading with your "personal best." That's the best reading you've ever had. Your doctor will help you establish your "personal best" early in your treatment.

Your doctor will help you set up three zones of peak flow meter readings.

1. Any reading in the green zone means your airways are open.
2. Any reading in the yellow zone means you may be at risk for a flare-up or you might already be having some symptoms. Talk to your doctor about what to do for readings in the yellow zone.
3. Any reading in the red zone means you need medication immediately and should see a doctor as soon as possible.

How Often Do You Use It?

Not everyone needs to use a peak flow meter regularly. Your doctor will let you know if it needs to be part of your regular asthma management schedule. But if you take asthma medicine every day, you may need to use your peak flow meter once or twice a day.

Your doctor might ask you to record the results and bring them with you to your appointments. This gives the doctor important information needed to determine the right treatment for you.

It can feel like a hassle to have to take peak flow readings, especially when you aren't having any breathing problems. But it's much worse to have an unexpected flare-up that could ruin your day or your plans for the evening.

For all their hard work, what do peak flow meters ask of you? Just to be kept clean. Wash yours regularly with mild soap and hot water.

Reviewed by: Elana Pearl Ben-Joseph, MD
Date reviewed: August 2011
Originally reviewed by: Nicole Green, MD