Nineteen patients were challenged with TDI and three patients received HDI (patients 16, 21, and 22). Patient characteristics and results of challenge tests are summarized in Tables 1, 2
, respectively. Four of 22 patients had normal PC20 values at baseline. The first SIC with isocyanates elicited an asthmatic reaction in 13 patients (immediate [n = 6], late [n = 1], and dual [n = 6]). Two of these 13 patients had normal PC20 values at baseline, but PC20 fell within the asthmatic range after SIC with isocyanates. In five patients (patients 1, 2, 16, 17, and 21) who did not show an asthmatic reaction after the first SIC, PC20 exhibited a greater than twofold reduction after the isocyanate challenge: 21-fold, sevenfold, 2.5-fold, 2.6-fold, and threefold, respectively. In three patients (patients 1, 2, and 21), a second SIC with isocyanate elicited an immediate asthmatic reaction. In two patients (patients 16 and 17) in whom PC20 decreased 2.5-fold and 2.6-fold, respectively, the second isocyanate SIC result was negative. In the 14 patients in whom PC20 was monitored after the first isocyanate SIC, it varied from negative to positive in three patients and, in the remaining patients, it showed a reduction that ranged from 0.6-fold to 15.2-fold (mean, fourfold).