The International and "NIH" units for thrombin--how do they compare?

Area of Science:

• Biochemistry
• Biotechnology
• Pharmacology

Background:

• The International Standard (IS) for alpha-thrombin, established in 1991, relates to the 1975 1st IS for Thrombin, containing 100 IU.
• The National Institute of Health (NIH) standard (Lot J) is widely used for calibrating commercial thrombin reagents.

Purpose of the Study:

• To compare the unitage defined by the current International Standard (IS) for alpha-thrombin and the commonly used National Institute of Health (NIH) standard.
• To establish a precise conversion factor between NIH thrombin units and International Units (IU).

Main Methods:

• Comparative analysis of thrombin activity between the IS and NIH standards.
• Assays conducted in the presence and absence of Polyethylene Glycol (PEG) to assess its influence on unitage.
• Confirmation of unitage ratio using amidolytic assay data.

Main Results:

• One NIH unit of thrombin activity was found to be equivalent to 1.1 to 1.3 IU.
• The influence of PEG in the assay affected the observed unitage ratio.
• A recommended unitage ratio of 1.15 IU per NIH unit was determined after analyzing data with and without PEG.

Conclusions:

• The study provides a critical conversion factor for calibrating thrombin reagents using the NIH standard against the International Standard.
• A unitage ratio of 1.15 IU/NIH unit is recommended for accurate thrombin quantification.
• Understanding the impact of assay components like PEG is crucial for consistent thrombin unitage determination.