Comparison of exhaled nitric oxide (FeNO) values measured in patients with asthma with those expected based on the formula proposed by Dressel et al20 taking into account height, sex, atopy and smoking status*
| FeNO value based on Dressel et al20 | Geometric mean FeNO value for our population with asthma | Optimum cut-off point for identifying a sputum eosinophil count ≥3% | |
| Men, smokers, atopy | 20 | 50 | 31 |
| Men, non-smokers, atopy | 33 | 62 | 51 |
| Men, smokers, no atopy | 14 | 53 | 22 |
| Men, non-smokers, no atopy | 21 | 48 | 33 |
| Women, smokers, atopy | 16 | 35 | 39 |
| Women, non-smokers, atopy | 25 | 47 | 66 |
| Women, smokers, no atopy | 10 | 14 | 26 |
| Women, non-smokers, no atopy | 16 | 39 | 40 |
↵* FeNO (ppb)=17.49×(1.496 if atopy)×(0.627 if smoker)×(1.235 if infection)×(1.174 if male)×1.113 (height cm-170)/10)). Our observed values were much higher than expected, which highlights the importance of asthma as the major factor contributing to raised FeNO.