In the asthma red zone, what does a PEF reading of less than 50% of personal best indicate?

• A. PEF 60-79% of personal best
• B. PEF >=80% of personal best
• C. PEF <50% of personal best requiring urgent evaluation
• D. PEF 40-60% of personal best

Answer: (C)

In the red zone, the key idea is that the lungs are significantly obstructed and this requires immediate action. Peak expiratory flow (PEF) measures how fast air can be blown out; a personal best is the highest PEF the person achieves when asthma is well controlled. The red zone is defined by readings well below that personal best—specifically less than 50% of it. When PEF falls into this range, it signals severe airway narrowing consistent with a potentially dangerous asthma flare, so urgent evaluation and treatment are needed right away.

Context helps: in practice, you would use a peak flow meter to monitor daily, and if you see a PEF under 50% of your personal best, you should follow your action plan for red-zone symptoms, which typically involves using a prescribed rescue inhaler immediately and seeking urgent medical care if there is little or no improvement or if warning signs (extreme shortness of breath, inability to speak full sentences, confusion) are present. Readings in the yellow zone (about 50–79%) indicate a need to adjust management with medical guidance, while green (80% and above) indicates good control.