The Acetylcholinesterase (RBC) OPC test is a blood test to measure the activity of the acetylcholinesterase enzyme in red blood cells (RBCs). It is primarily used to detect and monitor organophosphate (OP) poisoning, especially in individuals with occupational exposure to pesticides. The test can also be used for other purposes, such as evaluating the risk of postoperative paralysis if a patient receives a muscle relaxant like succinylcholine.