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Changes in FeNO levels (ppb) with time after collection in relation to the initial values. Mylar bags were stored at 4°C (A) and room temperature (B) after collection of exhaled air. The subjects were divided into four groups by the quartiles of FeNO levels immediately after collection: Q1, ≥ 51.0 ppb; Q2, 30.4–50.5 ppb; Q3, 22.4–29.0 ppb; Q4, ≤ 20.0 ppb.
