Peak flow zones are a key component of asthma management plans and are used to interpret peak expiratory flow rate (PEF):how well air moves out of your lungs. These measurements are obtained with a peak flow meter.

These zones help individuals with asthma and their healthcare providers monitor asthma control and make informed decisions regarding medication adjustments and when to seek medical attention. Peak flow zones are typically divided into three categories: green, yellow, and red

Green Zone (80 to 100 percent of your personal best number) signals all clear. No asthma symptoms are present. Take your daily controller medicines (if prescribed), as usual.

Yellow Zone (50 to 80 percent of your personal best number) signals caution. You should take a quick-relief medicine and check to see if your peak flow returns to the green zone. You may be having an asthma episode that requires an increase in your medicines or the addition of new medicines. Or your overall asthma may not be under control. Follow your Asthma Action Plan and seek additional medical care as indicated.

Red Zone (below 50 percent of your personal best number) signals a medical emergency. You must take your quick-relief medicine right away. Call your doctor immediately if your peak flow number does not return to the yellow or green zone and stay in that zone. If you cannot reach your doctor and your peak flow stays in the red zone, go directly to the emergency room. Your Asthma Action Plan should provide clear instructions.

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