How is tetanus skin test fluid prepared?

Tetanus antitoxin, it is easy to cause allergies in the human body, so before injection is required to carry out allergy test. In the preparation of tetanus skin test solution, you need to take out 0.1 ml of solution, and then add 1% sodium chloride solution, diluted to 1 ml, each ml contains 150 units, then tetanus skin test solution is prepared. Skin tests on the forearms take 30 minutes to determine results, and if the anterior wall shows redness or itching, allergies are suspected.