Key result
One NIH unit of thrombin equals ~1.15 IU based on comparative assays.
Effect estimate: 1 NIH unit = 1.1 to 1.3 IU
This study establishes a conversion factor of 1.15 to equate NIH units of thrombin to International Units, facilitating standardized calibration of commercial thrombin reagents.
May support standardized thrombin reagent calibration in labs; leaves open clinical validation of the conversion.
The current International Standard (IS) for alpha-thrombin was established in 1991. It was related in unitage with the 1st IS for Thrombin established in 1975 and contains 100 IU of thrombin activity. The National Institute of Health (NIH) standard (Lot J) is in common use for the calibration of commercial thrombin reagents and this study reports on a comparison of the thrombin units defined by these 2 standards. This study has indicated that one "NIH" unit is equivalent to 1.1 to 1.3 IU of thrombin, depending on the influence of PEG in the assay. A unitage ratio figure of 1.15 was recommended following analysis of data obtained in the presence and absence of PEG in the comparative assays. This was confirmed by amidolytic assay data.
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Gaffney et al. (1995) studied this question. NIH standard (Lot J) for thrombin vs. International Standard (IS) for alpha-thrombin was evaluated on Comparison of thrombin units defined by the two standards (1 NIH unit = 1.1 to 1.3 IU). One NIH unit of thrombin is equivalent to 1.1 to 1.3 International Units (IU), with a recommended unitage ratio of 1.15 based on comparative assays.
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