This specialized laboratory test is performed after an elevated prolactin level is detected in the serum. It detects the presence and amount of macroprolactin, a large complex consisting of normal prolactin (monomer) bound to autoantibodies (IgG). This large complex is biologically inactive, but it is detected by most routine assays, leading to a falsely elevated prolactin reading. The test is used to confirm or rule out pseudo-hyperprolactinemia (macroprolactinemia).