Peak flow meter: how to use it, find your personal best, and read the zones
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- Mechanical peak flow meter. Best for: Simple daily readings at home. See options on Amazon
- Digital peak flow meter. Best for: People who want readings stored. See options on Amazon
- Second peak flow meter, same brand. Best for: A child's school or a workplace. See options on Amazon
What a peak flow meter does
NHLBI says measuring your peak flow can help you know how well your asthma is controlled, alert you to an oncoming attack, and during an attack tell you how bad it is and whether your medicine is working. It also helps you and your provider learn what makes your asthma worse, decide whether your treatment plan is working, decide when to add or stop medicine, and decide when to seek emergency care.
The FDA classifies a peak-flow meter for spirometry as a device used to measure a patient's maximum ventilatory flow rate, a Class II device under 21 CFR 868.1860.
How to take a reading
NHLBI's steps:
- Always stand up, and remove any food or gum from your mouth.
- Make sure the marker is at the bottom of the scale.
- Breathe in slowly and deeply, and hold that breath.
- Place the mouthpiece on your tongue and close your lips around it for a tight seal; do not put your tongue in the hole.
- Blow out as hard and fast as possible.
- Write down the number next to the marker. If you cough or make a mistake, do not write it down; do it over.
- Repeat two more times and record the highest of the three numbers in a notebook, calendar or asthma diary.
NHLBI also suggests asking your doctor, pharmacist or another health care professional to show you how to use your meter.
Finding your personal best
NHLBI defines your personal best as the highest peak flow number you get over a 2-week period when your asthma is under good control, meaning you feel good and have no symptoms. To find it, take readings:
- At least twice a day for 2 to 3 weeks.
- When you wake up and in late afternoon or early evening.
- 15 to 20 minutes after you take your quick-relief medicine.
- Any other time your provider suggests.
Write down every reading. MedlinePlus notes your personal best can change over time, so ask your provider when to check for a new one.
The three peak flow zones
| Zone | Percent of personal best | What NHLBI says it signals |
|---|---|---|
| Green (Go) | 80 to 100 percent | Good control and no asthma symptoms |
| Yellow (Caution) | 50 to 79 percent | Asthma is getting worse; add quick-relief medicine per your plan |
| Red (Medical Alert) | Less than 50 percent | Add or increase quick-relief medicine per your plan and call your doctor now |
Ask your provider to write on your asthma action plan the numbers for each zone and the medicines and steps for each. NHLBI suggests marking the zones on your meter with colored tape or a marker. If you take daily long-term control medicines, keep taking them in every zone, NHLBI says.
Daily use
Once you know your personal best, NHLBI says to take your peak flow every morning when you wake up, before your asthma medicine, and check the number against the zones on your action plan. Also use the meter when you are having symptoms or an attack: take your medicine first, then your peak flow, to see whether the medicine is working or you need more treatment.
NHLBI's asthma pages add that a low number can warn you of an attack even before you notice symptoms, and to bring your record to your next care visit.
Choosing a meter
- Stick with one brand. MedlinePlus says that if you use more than one meter, such as one at home and one at school or work, all of them should be the same brand.
- Children. MedlinePlus notes many children under age 5 cannot use a peak flow meter very well, though some can, and starting before age 5 can get a child used to it.
- Mechanical or digital. Whichever type you choose, use the same steps and record the highest of three blows.
- Keep a log. A notebook, calendar or app makes it easier to spot changes and share them with your provider.
For other breathing gear, see our pulse oximeter guide.
What to look for when you buy
Mechanical peak flow meter
Best for: Simple daily readings at home
Uses the marker-and-scale steps NHLBI describes for a reading.
Watch out: Reset the marker to the bottom of the scale before each blow.
See options on AmazonDigital peak flow meter
Best for: People who want readings stored
Stored readings can make it easier to keep the record NHLBI suggests bringing to visits.
Watch out: Use the same brand at home and school or work, per MedlinePlus.
See options on AmazonSecond peak flow meter, same brand
Best for: A child's school or a workplace
MedlinePlus says multiple meters should all be the same brand.
Watch out: Mark the zones from the action plan on each meter.
See options on AmazonQuestions people ask
- When should I use my peak flow meter?
- NHLBI says every morning before your asthma medicine, and when you have symptoms or an attack.
- How do I find my personal best?
- Take readings at least twice a day for 2 to 3 weeks while your asthma is under good control.
- What do the peak flow zones mean?
- Green is 80 to 100 percent of your personal best, yellow 50 to 79, and red less than 50.
- What should I do in the red zone?
- NHLBI says add or increase quick-relief medicine per your action plan and call your doctor now.
- Can young children use a peak flow meter?
- MedlinePlus says many children under 5 cannot use one very well, but some can.
Sources
- Monitoring Your Asthma (fact sheet) (nhlbi.nih.gov), National Heart, Lung, and Blood Institute
- Asthma: Living With (nhlbi.nih.gov), National Heart, Lung, and Blood Institute
- How to use your peak flow meter (medlineplus.gov), MedlinePlus Medical Encyclopedia
- 21 CFR 868.1860 Peak-flow meter for spirometry (ecfr.gov), eCFR