More on Polycythemia and Anticoagulant Volume

More on Polycythemia and Anticoagulant Volume
Feb 9, 2017 12:22pm

More on anticoagulant adjustment from Heather DeVries: There is more to our story on adjusting sodium citrate for high hematocrits. We have a pediatric patient who is getting multiple draws, for multiple assays, throughout the day. Sometimes there is PT and/or PTT , but sometimes not. The techs are confused as to when the draw must be in a corrected tube. We all understand how the citrate is affecting the results due to its relationship with calcium, but what about when an anti-Xa level is drawn, or an ATIII (antithrombin, AT ) functional? If those are the only assays ordered, must the tube be corrected? The patient's hematocrit has been hovering around 60%. Thanks, Heather.

Thank you, Heather, and I hope your staff and pathologist are communicating with the child's care team to ensure they are not causing a hospital acquired anemia. I'll go out on a limb in the absence of empirical outcomes data and agree with your staff that any clot-based assay is likely to be influenced by the anticoagulant to plasma ratio, but not an immunoassay or a chromogenic substrate assay. If your antithrombin assay is a chromogenic assay, you would be safe to use a standard draw. Perhaps one of our participants knows of a study supporting this conclusion.

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More on anticoagulant adjustment from Heather DeVries: There is more to our story on adjusting sodium citrate for high hematocrits. We have a pediatric patient who is getting multiple draws, for multiple assays, throughout the day. Sometimes there is PT and/or PTT , but sometimes not. The techs are confused as to when the draw must be in a corrected tube. We all understand how the citrate is affecting the results due to its relationship with calcium, but what about when an anti-Xa level is drawn, or an ATIII (antithrombin, AT ) functional? If those are the only assays ordered, must the tube be corrected? The patient's hematocrit has been hovering around 60%. Thanks, Heather.

Thank you, Heather, and I hope your staff and pathologist are communicating with the child's care team to ensure they are not causing a hospital acquired anemia. I'll go out on a limb in the absence of empirical outcomes data and agree with your staff that any clot-based assay is likely to be influenced by the anticoagulant to plasma ratio, but not an immunoassay or a chromogenic substrate assay. If your antithrombin assay is a chromogenic assay, you would be safe to use a standard draw. Perhaps one of our participants knows of a study supporting this conclusion.

By Clinical Research Scientist David McGlasson
Feb 11, 2017 8:33am
Heather, see the following reference: McGlasson DL, Kaczor DA, Krasuski RA, et all. Effects of pre-analytical variables on the anti-activated factor X chromogenic assay when monitoring unfractionated heparin and low molecular weight heparin anticoagulation. Blood Coagul Fibrinolysis 2005;16: 173–6. It refers to the work that I did when working on the hybrid curve for anti-Xa testing for the heparinoids. We purposely drew regular blue tops with a 9:1 and a 6:1 blood to anticoagulant ratio. The clottable assays were affected but there was no clinical or significant difference with the chromogenic assays with any of the heparins tested. We also published a paper dealing with this issue in Lab Medicine 2005. Using a single calibration curve with the anti-Xa chromogenic assay for monitoring heparin anticoagulation that used a similar patient population and found the same results.

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