Correlation between Blood Eosinophilia and Fractional Exhaled Nitric Oxide in the diagnosis of Asthma within Primary Care

Background and Aims: There is overwhelming evidence that detection of eosinophilic airway inflammation is superior to clinical history in making asthma diagnosis. However, the use of Fractional Exhaled Nitric Oxide (FeNO) in primary care has met with scepticism by UK guidelines. Our study set out to investigate whether there was a correlation between FeNO and blood eosinophilia in patients suspected of Asthma on clinical history. Methods: Eighty two suspected Asthma patients underwent Full Blood count, Spirometry and FeNO testing at first assessment of their symptoms at a single GP centre between February and December 2019. Results: The age range of the patients were 12 to 52. A total of 66 patients (81%) were diagnosed with Eosinophilic and Non-Eosinophilic Asthma during the study period. 19 patients (24%) demonstrated positive reversibility at Spirometry. 17 of these patients had raised FeNO levels (>40 bbp) and only 14 of these patients had raised blood eosinophil count (>0.4 X109 /L). FeNO levels were raised in 64 patients in total and this correlated to 61 patients (96%) with higher than normal blood eosinophilia count (mean= 0.49 ± 0.05 X109/L). The remaining 3 patients did not have significant reversibility at spirometry. All 66 patients were initiated on inhaled steroid therapy. All but one had complete resolution of symptoms at 6 weeks. Conclusions: Our study demonstrates that it is possible to diagnose Asthma in primary care by using clinical assessment and blood eosinophilia as the biomarker and that FeNO should only be used in selective diagnostic difficulties. A larger prospective trial is required to verify these results