On January 20, 2015, the Supreme Court provided guidance on the standard of review for claim construction on appeal in Teva Pharmaceuticals USA, Inc. v. Sandoz, Inc., No. 12-854. The Court held “[w]hen reviewing a district court’s resolution of subsidiary factual matters made in the course of its construction of a patent claim, the Federal Circuit must apply a ‘clear error,’ not a de novo, standard of review.”

The Court stated:

[W]hen the district court reviews only evidence intrinsic to the patent (the patent claims and specifications, along with the patent’s prosecution history), the judge’s determination will amount solely to a determination of law, and the Court of Appeals will review that construction de novo.

…

In some cases, however, the district court will need to look beyond the patent’s intrinsic evidence and to consult extrinsic evidence in order to understand, for example, the background science or the meaning of a term in the relevant art during the relevant time period … In cases where those subsidiary facts are in dispute, courts will need to make subsidiary factual findings about that extrinsic evidence. These are the “evidentiary underpinnings” of claim construction that we discussed in Mark-man, and this subsidiary fact finding must be reviewed for clear error on appeal.