What Causes Swelling And Itching At Injection Site?

Good day. I m a renal patient and I have my blood chem done periodically. I m just wondering why my left arm where my blood is drawn got swollen and is very itchy I could not help scratching it. My med tech could not draw blood from my left so he did it on the right arm. Now both arms are itching right on the area pricked. What could be the reason? Is my disease getting worse?