Geometric Mean & VRI

The Geometric Mean & VRI module establishes the Normal Patient Mean (NPM) for a PT reagent-instrument combination and verifies that the reagent's reference interval is appropriate for the local patient population. The Normal Patient Mean is the geometric mean of Prothrombin Time (PT) results collected from healthy subjects using the specific reagent lot being calibrated. It serves as the denominator in the INR calculation and must be determined for each new reagent lot before the lot is placed into service.

The Verified Reference Interval (VRI) component confirms that the configured PT and INR reference limits are appropriate — specifically, that no more than 10% of the normal population falls outside those limits. Together, these two components satisfy the calibration and verification requirements for PT/INR testing that are mandated by accreditation standards.

When to Use This Module

This module is required in the following situations:

• New reagent lot — Every time a new thromboplastin reagent lot is placed into service, a new Normal Patient Mean must be established. The NPM is lot-specific; using an NPM from a different lot introduces systematic INR error.
• New coagulation analyzer — When a new instrument is introduced or an existing instrument is repaired, the NPM must be re-established on that specific analyzer using the current reagent lot.
• Reference interval verification — Laboratories are required to verify that their PT and INR reference intervals are appropriate for their local patient population. This module performs that verification using the same normal subject dataset collected for the NPM.
• Accreditation requirements — CAP, The Joint Commission, and CLIA require documentation of NPM establishment and reference interval verification for PT/INR testing. This module generates the compliant report that satisfies those requirements.