45 CFR §800.504

1. (a)OPM's written decision under the external review process established under § 800.503(a) of this part will constitute final agency action that is subject to review under the Administrative Procedure Act in the appropriate U.S. district court. A decision made by an independent review organization under the process established under § 800.503(a) is not within OPM's discretion and therefore is not final agency action.
2. (b)Judicial review under paragraph (a) of this section is limited to the record that was before OPM when OPM made its decision.