The International System of Units (SI), commonly known as the metric system, is the international standard for measurement. According to the National Institute of Science and Technology (NIST), the SI rests on a foundation of seven defining constants: the cesium hyperfine splitting frequency, the speed of light in vacuum, the Planck constant, the elementary charge (i.e., the charge on a proton), the Boltzmann constant, the Avogadro constant, and the luminous efficacy of a specified monochromatic source.
SI and the Regulatory Environment
The Japanese PMDA requires the use of SI units. For further information, please refer to the PMDA FAQs on Electronic Data Submission.
The US FDA expects SI units to be used in the Laboratory Findings (LB) domain, but may request a custom domain that represents laboratory findings using US conventional units, as explained in the Study Data Standards Technical Conformance Guide.
CDISC does not provide a specific solution when a sponsor is asked to provide both. If a sponsor anticipates an FDA request for conventional units, they can produce a custom domain (e.g., an LC, Laboratory Findings in Conventional Units, domain) in addition to the LB domain using SI units.