Introduction: The forced expiratory volume 0.75 seconds (FEV0.75s) measurements is a surrogate tool of the standard FEV1s. There is actually an urgent need to determine bronchodilator response cut-off points for children.

Aim: To determine the cut-off values for positive bronchodilator response in asthmatic Tunisian children using the FEV0.75 s.

Method: We have conducted a retrospective study, involving asthmatic children aged between 5 and 16 years old in the Physiology and functional exploration department of Habib Bourguiba hospital of Sfax. Spirometry was performed before and after BD. Significant BDR was established according three definitions; the GINA 2022 (D12) (increase of FEV1 by 12 % of predicted value),the D18 by  Edjane Figueiredo Burity, 2016( increase of FEV0.75s by 18 % of the initial value), the D14 by Luis Miguel Borrego 1, 2013 ( increase of FEV0.75s by 14 % of the initial value). 

Results: Eighty-four boys and forty-three girls, with a mean age (years) 9,95 ±2,7, were included. The bronchodilator response was significant in 20.5 % ,26 % and 21.3 % according the D18, D14 and D12. Among 27 children with a significant BDR based on D12, 66,7 % have an increase of their FEV0.75 more than 18 % and 81.5 % more than 14 % (p <0.05). By contrast ,10.5 % and 7.4 % of children have a significant D14 and D18 without a significant D12. Using the ROC curve a cut-off points of 12.75 % for the FEV0.75 seems suitable with a high sensitivity (92.6 %) and a specificity (86.2 %) in the Tunisian population.

Conclusion:The cut-off values identified in this study will be useful for evaluating bronchodilator response by the FEV0.75 s in asthmatic Tunisian children.