How do you obtain blood from a arm with IV?

To obtain blood from an arm with an IV, first ensure that the IV line is functioning properly and that the blood draw won't interfere with the IV fluids being administered. Use a separate venipuncture site if possible, or if drawing from the IV line, clamp it and flush with saline to ensure it's patent. After clamping, draw the required blood volume into the appropriate collection tubes, then flush the line again with saline and remove the clamp. Always follow your institution's protocols for blood collection and ensure proper labeling and handling of the samples.