Why should you avoid using the arm on the same side of a mastectomy?

Choosing to avoid using the arm on the same side of a mastectomy primarily relates to the prevention of complications such as lymphedema. After a mastectomy, the lymph nodes in the armpit may be removed or damaged, which can disrupt the normal lymphatic drainage. When blood is drawn from the arm on the same side as the surgery, it can increase the risk of fluid accumulation, leading to swelling (lymphedema). This condition can be uncomfortable and may require ongoing management.

Additionally, using the arm on the same side as the mastectomy could exacerbate any existing complications or lead to further medical issues in patients with compromised lymphatic systems. Therefore, it is standard practice to use the contralateral arm to minimize these risks and ensure patient safety.