Repeatability of bronchial responsiveness to mannitol dry powder in children with asthma.

Our objective was to determine the repeatability of bronchial responsiveness to mannitol dry powder (MDP) as an objective marker of asthma in children. MDP challenge was performed in children with stable asthma at the same time of the day on two separate occasions within a week. The test was terminated after a 15% fall of forced expiratory volume in 1 sec (FEV1) and the provocative dose to produce a 15% fall in FEV1 (PD15) were calculated. Seventeen children (aged 9-16 years) on inhaled corticosteroids (200-1,500 mcg) were studied. Mean baseline FEV1 before the challenges were 95% (81-119) and 96% (74-121), respectively, with a standard deviation of differences of 5.2%. PD(15) values ranged from 7-387 mg, with a geometric mean of 38 mg for the first and 49 mg for the second test. Of the 17, all but two pairs of tests achieved a PD15 within one dose of capsules. Four children had a negative challenge on two occasions. A high relative reliability was reflected by a concordance coefficient of 0.86. In conclusion, MDP is a convenient challenge which is easy to administer and is well-tolerated by children. It is a highly reproducible test of airway responsiveness in children with moderate to severe persistent asthma on inhaled corticosteroids within 7 days under laboratory conditions.