Legion Diagnostics

Factor Sensitivity

The Factor Sensitivity module characterizes how well a coagulation reagent detects reduced activity of a specific clotting factor. Because coagulation reagents vary in their ability to respond to factor deficiencies, laboratories must verify that a reagent is appropriately sensitive — capable of producing abnormal clotting times when factor activity falls below clinically meaningful thresholds. A reagent that is insensitive may fail to flag a deficient patient as abnormal; one that is hypersensitive may generate false alarms in patients with borderline factor levels.

The study is performed by testing serial dilutions of reference plasma mixed with factor-deficient plasma across the PT or aPTT pathway, then fitting a regression curve to determine the factor activity percentage at which the clotting time crosses the Upper Limit of the Normal Range (ULNR). Two sensitivity estimates are reported: First Abnormal Dilution (the highest dilution at which the mean clotting time is already above the ULNR) and Calculated Sensitivity (the regression-derived crossover point).

When to Use This Module

Factor sensitivity studies are required in the following situations:

  • New reagent lot implementation — Sensitivity can vary between reagent lots for the same analyzer. A new factor sensitivity study should be performed each time a new reagent lot is placed into service, as the ULNR is specific to the reagent lot being used.
  • New coagulation analyzer implementation — When placing a new analyzer into service, factor sensitivity must be characterized to confirm that the instrument-reagent combination detects clinically significant factor deficiencies within acceptable limits.
  • Reagent reformulation — If a reagent manufacturer reformulates their product, the sensitivity profile may change even if the lot number is updated. A new study is recommended.
  • Periodic verification — Some laboratory accreditation standards and institutional policies require periodic re-evaluation of reagent sensitivity to confirm ongoing performance over time.
  • Accreditation requirements — CAP (College of American Pathologists) and The Joint Commission require laboratories to document performance characteristics for coagulation reagents, including sensitivity to clinically relevant factor deficiencies.