Effects of Pre-Analytical Variables on the Anti-FXa Chromogenic Assay when Monitoring Unfractionated Heparin and Low Molecular Weight Heparin Anticoagulation.

Published

Conference Paper

Abstract Introduction: The purpose of this study was to determine if the anti-FXa (FXa)assay is less affected by pre-analytical variables in monitoring patients on unfractionated heparin (UFH) and low molecular weight heparin (LMWH) than the activated partial thromboplastin time (APTT). Methods: Twenty-six subjects receiving enoxaparin (LMWH) in varying concentrations were randomly selected and consented for this study. Twenty individuals receiving UFH were also randomly selected and consented. Each study subject had 6 tubes of citrated blood obtained by venipuncture in a one-time blood draw. Two vacutainer tubes were 3.8% sodium citrate, two were 3.2% sodium citrate, and two had an anticoagulant called CTAD. All of the tubes were from Becton-Dickinson, Inc. One tube from each set had a blood to anticoagulant ratio of 9:1. The other tube had an intentional “short-draw” of approximately 6:1 blood to anticoagulant ratio. All six specimens on each subject had an APTT and a FXa assay corresponding to the type of heparin they were receiving performed by a kit from Diagnostica-Stago, Inc., called STA-Rotachrom Heparin Assay. All tests were performed on an STA-R automated coagulation analyzer. Each FXa heparin assay was performed using either a standard UFH or LMWH calibration curve and a HYBRID curve using a specific combination of calibrators. An ANOVA statistical test and descriptive statistics were used to compare each set of results. Results: The UFH APTT had a mean range of 100.1–127.2 seconds. The 3.8% short draw tube had the highest mean. The ANOVA however was p=0.9845. The UFH FXa mean range with all 6 tubes was 0.32–0.37 IU/mL. The ANOVA for the UFH curve had a p value of 0.9878. With the HYBRID curve the mean range was 0.34–0.39 IU/mL with a p value of 0.9961. When comparing the six UFH results with the six HYBRID curves data the ANOVA p value was 0.9994. The CTAD tubes gave the highest levels of UFH. The LMWH APTT had a mean range of 37.1–41.2 seconds. The highest mean was the CTAD normal draw tube. The LMWH assay curves had a mean range of 0.37–0.46 IU/mL with the CTAD normal draw tube again having the high recovery of heparin. The ANOVA result had a p value of 0.9060. The HYBRID curve had a mean range of 0.42–0.49 IU/mL and again the CTAD normal draw tube displayed the highest amount of heparin. The ANOVA p value was 0.9379. When comparing the 6 LMWH results with the 6 HYBRID results the ANOVA p value was 0.9512. Discussion: The APTT results were skewed. In one subject the APTT was 48 seconds and another around 114 seconds with the same amount of UFH detected. This makes the so-called therapeutic range suspect. The UFH and LMWH data compared to the HYBRID curves was excellent clinically and statistically. This data demonstrates that the laboratory could use a single calibration curve for monitoring both UFH and LMWH subjects. The intentional short draw tube did not seem to affect the FXa assay. The FXa assay appears to be a better method monitoring heparin subjects than the APTT. The APTT was largely unaffected in subjects on LMWH and is not normally used to monitor individuals on this anticoagulant.

Full Text

Duke Authors

Cited Authors

  • McGlasson, DL; Kaczor, DA; Krasuski, RA; Campbell, CL; Kostur, MR; Adinaro, JT

Published Date

  • November 16, 2004

Published In

Volume / Issue

  • 104 / 11

Start / End Page

  • 4064 - 4064

Published By

Electronic International Standard Serial Number (EISSN)

  • 1528-0020

International Standard Serial Number (ISSN)

  • 0006-4971

Digital Object Identifier (DOI)

  • 10.1182/blood.v104.11.4064.4064