The exact procedure may vary slightly depending on the reason for the scan (the suspected problem). The RBCs are tagged with radioisotope in 1 of 2 ways. First, a sample of blood may be withdrawn from the person in the standard venipuncture method (similar to getting a sample for a blood test). In the laboratory, the RBCs are separated from the rest of the blood components and mixed with the radioisotope. A short time later these tagged RBCs are reinjected into a vein. The second method involves injection of a medication that sensitizes the RBCs in the body, which is a complex chemical reaction that permits the RBCs to accept the radioisotope (attach the isotope to the cell membrane). The isotope is injected into a vein 15 or 20 minutes later. Scanning may be performed immediately, after a delay, or a series of scans may be performed. The whole body or only particular locations may be scanned depending on the indications for the test. The person lies on a table while the scanner detects the location and amount of radiation emitted by the tagged RBCs.
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