@article {MurrayA179, author = {CS Murray and P Foden and LA Lowe and H Durrington and A Custovic and A Simpson}, title = {P176 Diagnosing asthma in children using spirometry: evidence from a birth cohort study}, volume = {71}, number = {Suppl 3}, pages = {A179--A179}, year = {2016}, doi = {10.1136/thoraxjnl-2016-209333.319}, publisher = {BMJ Publishing Group Ltd}, abstract = {Background NICE draft guidance for the diagnosis of childhood asthma proposes algorithms based on four tests of lung function (FEV1/FVC ratio, bronchodilator reversibility [BDR], FeNO, PEFR variability); a minimum of two tests must be positive to make a diagnosis. For FEV1/FVC ratio, the proposed cut-off for a positive test is \<70\%, or the lower limit of normal (LLN), which is neither defined nor widely available. In this algorithm, spirometry is the first-line investigation, and children with FEV1/FVC \> 70\% are not offered BDR. However, the diagnostic test accuracy for FEV1/FVC and BDR is unknown. Within the setting of a population-based birth cohort we investigated the value of FEV1/FVC and BDR in diagnosing asthma.Methods We assessed study participants at clinical follow-up at age 16 years using validated questionnaires and lung function measurement. Spirometry was measured according to ATS/ERS guidelines. Using the Asthma UK reference equations, we calculated LLN for FEV1/FVC. BDR was considered positive if FEV1 increased by \>12\% following administration of 400 mg of salbutamol. Current asthma was defined as all three of: (1) doctor-diagnosed asthma ever, (2) wheezing in the previous 12 months and (3) current use of asthma treatment. We assigned children negative to all three features as a non-asthmatic control group.Results Spirometry was available for 630 children (325 boys, age range 13.1{\textendash}16.9 years), of whom 74 (11.7\%) had current asthma and 403 were assigned as non-asthmatic controls. FEV1/FVC was significantly lower among asthmatics (84.1\% vs. 89.2\%, p \< 0.001, Figure 1). Ten children (1.6\%) had FEV1/FVC \<70\% (two in asthma group). Discriminative ability of FEV1/FVC \< 70\% was poor (Receiver operating characteristic curve, AUC = 0.70; sensitivity = 2.7\% [2/74], specificity = 98.8\% [398/403]). For the calculated FEV1/FVC LLN (74.8\% for boys, 78.2\% for girls), 28 children (4.4\%) had FEV1/FVC\<LLN (11 in asthma group). Discriminative ability of FEV1/FVC\<LLN was poor (sensitivity 14.9\% [11/74]; specificity 97.0\% [391/403]). BDR was positive in 54 children (8.7\%), of whom 12 had asthma. Discriminative ability of BDR was poor (AUC = 0.64, sensitivity = 16.2\% [12/74], specificity = 93.5\% [373/399]). Combining these two tests did not result in a better diagnostic accuracy (sensitivity = 2.7\%, specificity = 99.0\%).Abstract P176 Figure 1 Conclusions FEV1/FVC \< 70\% or \<LLN, and BDR \> 12\% have a poor diagnostic accuracy as tests for childhood asthma.}, issn = {0040-6376}, URL = {https://thorax.bmj.com/content/71/Suppl_3/A179.2}, eprint = {https://thorax.bmj.com/content/71/Suppl_3/A179.2.full.pdf}, journal = {Thorax} }