A RN is caring for a client who is receiving a blood transfusion and develops urticaria one-half hour after the transfusion has begun. What is the first action the RN should take?

Stop the infusion.

Explanation:

The blood transfusion can cause sometimes problem to the patient in case when the mismatched blood is given in the patient's body. Sometimes the patient body is unable to uptake the foreign blood.

As the information in the question, the RN must stop the infusion. Urticaria represents the allergy in the blood plasma protein or the immune cell reaction in the body. The infusion is prevented as this might cause the destruction of immune cells in the body.

Thus, the answer is stop the infusion.