A MultiLaboratory Evaluation of a Chromogenic Factor X Assay for Monitoring Oral Anticoagulation The

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A Multi-Laboratory Evaluation of a Chromogenic
Factor X Assay for Monitoring Oral
Anticoagulation Therapy

• DL McGlasson1 PN Shaklee2 159th Clinical
  Research Squadron, Wilford Hall Medical Center,
  Lackland AFB, TX 2 Research Laboratory,
  BioCascade Incorporated, Arlington, WI
• This information is for education only and is not
  a product endorsement.

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INTRODUCTION

• Monitoring subjects with the presence of a lupus
  anticoagulant (LA) on oral anticoagulant therapy
  (OAT) with a prolonged clottable PT/INR assay may
  be difficult.
• The chromogenic factor X assay has been shown to
  be a useful tool in the management of patients
  with lupus anticoagulants (inhibitors) who are
  receiving oral anticoagulant therapy (OAT).
• Useful to monitor subjects converting from
  Agatobran and Lepirudin (direct thrombin
  inhibitors) to coumadin.

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INTRODUCTION CONTINUED

• A multi-site and multi-instrument validation of
  the chromogenic DiaPharma Factor X Assay kit
  (DFX) was undertaken in order to evaluate the
  utility of the assay for measuring FX in subjects
  receiving OAT.
• The chromogenic FX assay has been suggested as an
  alternative approach to monitor patients on OAT
  who have the presence of an LA.

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MATERIALS AND METHODS

• The DFX micro titer method was compared to a
  clottable FX (CFX) method in Laboratory 1. All
  clottable assays were performed on the
  Diagnostica Stago Inc., STA automated coagulation
  analyzer using Neoplastine CI with a low ISI and
  other Stago reagents.
• All testing was performed on citrated
  platelet-poor plasma with platelet counts lt109/L
• A normal range was established with 30 normal
  subjects with no known clinical abnormalities.

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MATERIALS AND METHODS 2

• Clinical sensitivity was tested using 30
  specimens subjects on OAT. The specimens were
  assayed for FX levels by DFX and CFX and PT/INR
  tests were performed.
• Thirty-one specimens positive for the presence of
  either hemolysis (n9), icteric color (n2),
  lipemia (n5), heparin (n10) or LAs (n5) were
  analyzed by DFX and CFX to check for the
  influence of interfering substances.
• Nineteen subjects with the presence of an LA on
  OAT and an unstable INR with specimens taken at 8
  time points were evaluated by both methods.

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MATERIALS AND METHODS 3

• Laboratory 2 used an STA compact and reagents
  from Diagnostica Stago, Inc., to evaluate both
  the CFX and DFX methods.
• A normal range was established using 25 normal
  subjects on both methods.
• Fifty-five subjects on OAT were evaluated by both
  the CFX and DFX methods.
• Precision and accuracy testing using different
  levels of FX were analyzed by all methods at both
  institutions.

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Lab One RESULTS Normal range
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Lab One RESULTS OAT subjects
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Lab One RESULTS OATsubjects with presence of an
LA
10
Lab One RESULTS Interfering substances
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Lab Two RESULTS Normal range
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Lab Two RESULTS OAT
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RESULTS Precision and Accuracy Testing Lab One
and Two
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RESULTS Precision and Accuracy Testing Lab One
and Two

• Precision Data Laboratory 1 performed precision
  testing using times 10 replicates on 6 specimens,
  run on the DFX in the range of 10-120 activity.
  CV ranged from 1.9-10.4. Using 5 known standards
  for the DFX, assay accuracy ranged from
  99.2-100.8 recovery.
• Laboratory 2 performed precision testing on 3
  levels of FX (n12) for DFX (CV2.5-5.1), CFX
  (CV4.6-9.2)

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CONCLUSIONS

• The present studies of the DFX kit demonstrated
  the assays robustness, precision, accuracy and
  utility for monitoring patients on OAT with and
  without interfering substances, the presence of
  an LA or unstable INR.
• This assay should offer health care providers an
  option for monitoring patients receiving OAT,
  especially those where INR values may not be
  reliable when an LA is present, and when bridging
  Agatroban subjects to warfarin.

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