Can I ask about peak flow?

[AlwaysInMotion]

DS has had a cough for several months and has been given a peak flow meter with a diary to keep for a couple of weeks. I have to take the measurements in the morning and the evening.

Currently he is averaging 160-70 in the morning and 190-200 in the evening. He's 122 cm tall.

Does anyone know what these readings mean? I have a follow up appointment but it's not for another two weeks (long delays in our surgery) and I'm just looking for answers now I suppose.

To diagnose asthma we look for diurnal variation of 20% or more, i.e. morning reading 20% less than nighttime reading is good indicator of asthma. (Asthma nurse)

I used a peak flow on my ds when he had an endless cough as directed by my GP. Can't remember the results but it didn't seem to indicate asthma at the time. But he was diagnosed with a dust mite allergy, hayfever and eventually with allergic asthma. The hospital paediatrician said they don't use peak flow tubes much with young kids at the hospital and ran other lung tests to gauge lung function. But I think GPs are more inclined to use them. He's on antihistamine, Montelukast tablets and has a blue inhaler. Cough went after he was prescribed Montelukast.