A critical immunohematological screening test designated for the detection of unexpected or irregular circulating antibodies freely present within the blood serum. Functioning via the indirect antiglobulin (Coombs) methodology, the assay exposes the patient's serum to characterized reagent red blood cells to identify antibodies capable of causing hemolysis. It acts as an absolute prerequisite preventive measure preceding any blood transfusion process to guarantee donor-recipient compatibility, and is concurrently a standardized protocol in obstetrical care to proactively monitor alloimmunization during pregnancy.