This work was aimed to graphic analysis of informative reliability of FEV1 in the bronchodilation test assessed as the ratio to baseline or predictive values and to determine the optimal FEV1 cut-off in bronchial asthma (BA) patients. The study analyzed 529 bronchodilation test results in 365 BA patients. A control group included 48 persons. The FEV1 changes were calculated twice in each test: as ratios to the baseline and predictive values. A high diagnostic reliability of FEV1 in the

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... lation test as a percentage of baseline and predictive values was found in BA patients with baseline ventilation disorders using the ROC method. The informative reliability of the FEV1%pred. was worse. Graphic analysis of cut-off for FEV1 improvement made to distinguish positive or negative bronchodilation test results showed 10 % increase independently on the method. We propose the differentiated assessment of the bronchodilation test results using 10 % to 12 % cut-off depending on severity of ventilation disorders.