Used in clinical and research laboratories to measure the levels of active vitamin B12 (holotranscobalamin) in human serum or plasma. This assay helps assess early vitamin B12 deficiency, which is critical for diagnosing conditions like pernicious anemia, neurological disorders, and megaloblastic anemia. The kit enables sensitive and specific quantification of HoloTC, allowing for early detection before total B12 levels drop significantly. It supports studies on B12 metabolism, nutritional status, and related diseases, making it valuable in both diagnostic and research settings.