What is the 53 nkat vial of thrombin equivalent to in NIH units?

Based on an assay with S-2238™, for bovine thrombin, 1 NIH-U = 1.15 IU = 3.4 nkat. The DiaPharma bovine thrombin, 53 nkat (S-2238™) is equivalent to approximately 21 NIH-U or 25 IU.