Department of Medicine, Division of Respirology, Critical Care and Sleep Medicine, Royal University Hospital, University of Saskatchewan, Saskatoon, SK, Canada.
Chest. 2010 Aug;138(2 Suppl):18S-24S. doi: 10.1378/chest.10-0088.
Direct bronchoprovocation challenges (eg, methacholine), which act directly on a specific airway smooth muscle receptor, are the most commonly performed challenge tests. Cut points have been arbitrarily selected to give high sensitivity and negative predictive values. In subjects with clinically current symptoms (within a few days) who inhale methacholine without deep inhalations, a normal methacholine test (provocative concentration causing a 20% fall in FEV(1) [PC(20)] > 16 mg/mL) rules out (current) asthma with reasonable certainty. A positive test in the moderate or greater range (PC(20) < 1 mg/mL) has high specificity and positive predictive value, comparable to the indirect challenges. Values between these levels are consistent with, but not diagnostic of, asthma. The positive predictive value (for clinical asthma) will increase the closer the PC(20) is to 1 mg/mL, the higher the pretest probability is for asthma and the more the methacholine-induced symptoms resemble the naturally occurring symptoms. Direct challenges are more sensitive and less specific than indirect challenges (exercise, adenosine monophosphate, mannitol, etc).
直接支气管激发挑战（例如，乙酰甲胆碱）直接作用于特定气道平滑肌受体，是最常进行的挑战测试。切点是任意选择的，以获得高灵敏度和阴性预测值。在有临床当前症状（在几天内）的受试者中，如果他们不进行深呼吸而吸入乙酰甲胆碱，则正常的乙酰甲胆碱测试（引起 FEV1 下降 20%的激发浓度 [PC20] > 16 mg/mL）可以合理确定排除（当前）哮喘。在中度或更高范围内的阳性测试（PC20 < 1 mg/mL）具有高特异性和阳性预测值，与间接挑战相当。在这些水平之间的值与哮喘一致，但不能诊断为哮喘。阳性预测值（对于临床哮喘）将随着 PC20 接近 1 mg/mL 而增加，哮喘的术前概率越高，并且乙酰甲胆碱引起的症状越类似于自然发生的症状。直接挑战比间接挑战（运动、单磷酸腺苷、甘露醇等）更敏感但特异性更低。
