Enzyme Assays and Activity Units
Data sheets: Data sheets documenting the specific activity of HTI products are included in all shipments. The type of assay performed and an explanation of the units of activity are included in footnotes.
Assays and units: In general, the activities of HTI products are measured in standard PT and APTT based clotting assays where one unit of activity is defined as the amount of activity present in 1 ml of normal pooled human plasma. Exceptions to this rule include the following:
NIH Units: Thrombin Activity is reported in NIH units. This activity is determined by comparison to U.S. Standard Thrombin, Lot J.
Chromogenic Substrate Hydrolysis: The activity of some enzymes (ex. APC, plasmin) are determined by the rate of hydrolysis of chromogenic substrates. 1 unit of activity is defined as the hydrolysis of 1 µmole of substrate per minute, under defined reaction conditions. It should be noted that this activity is highly dependent on the particular substrate used, the concentration of substrate, pH, ionic strength and temperature. The conditions are specified on the product data sheet included in all shipments.