Used in biomedical research to quantify P21 protein levels in cell lysates or tissue samples. Helps assess cell cycle regulation, particularly in studies related to DNA damage, cellular senescence, and tumor suppression. Widely applied in cancer research to evaluate the activity of p53 pathways and response to chemotherapeutic agents. Enables high-throughput screening in drug development and toxicology studies where cell cycle arrest is a key endpoint. Provides a reliable, sensitive, and specific measurement of P21 concentration, supporting both basic research and clinical investigation.