Home Diagnostics, Inc. v. Lifescan, Inc.

Claim Broader than Preferred Embodiment


August 31, 2004


Last Month at the Federal Circuit - September 2004

Judges: Rader (author), Dyk, and Prost

In Home Diagnostics, Inc. v. LifeScan, Inc., No. 03-1370 (Fed. Cir. Aug. 31, 2004), the Federal Circuit reversed the district court’s claim-construction order, vacated the order entering judgment in favor of Home Diagnostics, Inc. (“Home Diagnostics”), and remanded the case for a determination of validity and infringement.

Home Diagnostics initiated the suit below by seeking a DJ that its Prestige blood-glucose meters do not infringe LifeScan, Inc.’s (“LifeScan”) U.S. Patent No. 6,268,162 (“the ‘162 patent”). LifeScan filed a counterclaim for infringement. Following a Markman hearing, LifeScan stipulated that it could not prove infringement given the district court’s claim construction. The district court dismissed LifeScan’s counterclaim and entered a final judgment of noninfringement in favor of Home Diagnostics.

The sole claim at issue, claim 4 of the ‘162 patent, recites a method of measuring blood glucose with a reflectance-reading device. In particular, a sample of whole blood applied to a test strip reacts with a reagent, whereupon reflectance readings are taken “at specified time intervals upon detecting a predetermined drop in reflectance.” The glucose concentration in the sample is calculated from one of the reflectance readings “upon detection of a suitably stable endpoint.”

The central dispute in this case focused on the meaning of “upon detection of a suitably stable endpoint.” The district court construed this language as limiting the claim to detection at the expiration of a predetermined time period—a construction that effectively precluded a finding of infringement against Home Diagnostics because its device did not detect reflectance readings at a predetermined time.

Rejecting the district judge’s narrow construction, the Federal Circuit found that the claim language does not explicitly require a predetermined time for the reaction, but instead measures the endpoint with reference to the stability of the reflectance. The Court pointed to the teaching of the specification as simply one means of determining when a “suitably stable endpoint” has been reached. The ‘162 patent describes a preferred embodiment using predetermined time periods, but describes no other embodiments in detail. Nevertheless, the Court found no disavowal of alternative methodology, because an applicant’s choice to describe only a single embodiment does not mean that the patent clearly and unambiguously disavows other embodiments. Rather, the preferred embodiment is just one way of using the invention.

In addition, the Court noted that prior art identified by the ‘162 patent recites various methods of monitoring a reaction and cited these teachings as further evidence that one of ordinary skill would understand the claims as not limited to predetermined timing methods. Finally, the Court noted that during the prosecution of the family of patents including the ‘162 patent, LifeScan sought progressively broader claim language culminating in the limitation at issue in this case. The Court found that this course of prosecution showed that LifeScan purposefully sought claim scope in the ‘162 patent broader than the predetermined timing method disclosed. Thus, finding no disavowal, the Federal Circuit found that LifeScan was entitled to the full scope of its claim language and remanded for determinations on the liability issues.