Estimate n with the formula: n = TP: true possitive FN: false negative Calculate TP + FN: TP+FN = Z2: constant of normal distribution, with α = 0, 05, Z 2 = 1, 96 SN: minimal sensitivity, 75% (0, 75), W: odd of the probability of true positive results and probability of true negative results, select w = 0, 1 Therefore: TP + FN = (1, 96 x 0, 75 x 0, 25) / (0, 1 x 0, 1) = 36, 75 Based on the numbers of snakebite patients admitted to the Poison center, the minimal of cobrabite is 33%.