Factors Influencing Anti-Xa Assays: A Multicenter Prospective Study in Critically Ill and Noncritically Ill Patients Receiving Unfractionated Heparin

Abstract

Background The presence of dextran sulfate (DS) in reagents and the type of blood collection tube (citrate/citrated-theophylline-adenosine-dipyridamole [CTAD]) can lead to discrepancies between unfractionated heparin (UFH) anti-Xa levels. Objectives To evaluate the extent of the effect (1) of different reagents containing or not containing DS and (2) of the blood collection tubes, on UFH anti-Xa levels, in various clinical situations (NCT04700670). Methods We prospectively included patients from eight centers: group (G)1, cardiopulmonary bypass (CPB) after heparin neutralization (n = 39); G2, cardiothoracic intensive care unit (ICU) after CPB (n = 35); G3, medical ICU (n = 53); G4, other medical inpatients (n = 38). Blood was collected into citrated and CTAD tubes. Chromogenic anti-Xa assays were centrally performed, using seven reagent/analyzer combinations including two without DS. The association between anti-Xa levels and covariates was tested using a linear mixed-effects model. Results We analyzed 4,546 anti-Xa values from 165 patients. Median anti-Xa levels were systematically higher with reagents containing DS, whatever the patient group, with the greatest effect observed in G1 (0.32 vs. 0.05 IU/mL). Anti-Xa levels were slightly higher in CTAD than in citrate samples, irrespective of the assay. The model showed: (1) a significant dextran–patient group interaction (p < 0.0001), the effect of DS on anti-Xa levels varying from 30.9% in G4 to 296% in G1, and (2) a significant effect of CTAD, varying between patient groups (p = 0.0302). Conclusion The variability of anti-Xa levels with a great overestimation of the values, using a reagent containing DS, can lead to different treatment decisions, especially after heparin neutralization by protamine. Clinical consequences of these differences remain to be demonstrated.

Reassessment of dextran sulfate in anti-Xa assay for unfractionated heparin laboratory monitoring

“…This effect had already been identified for protamine sulfate by Mouton et al. [ 5 ] and more recently in the DEXHEP trial [ 43 ], but the effect of the added concentration of DS had never been studied so far.…”

“…One limitation of this study is its in vitro design. However, previous studies performed using in vivo samples of patients receiving UFH also identified increased FXa inhibition after the addition of low DS concentration [ 5 , 43 ]. Second, we used commercial NPP produced by plasmapheresis, which could behave differently from PPP obtained by direct blood collection and centrifugation.…”

“…The effect of DS could therefore be less in patient samples than in in vitro spiked ones, since the longer the chains, the more their binding to heparin interactome. However, the DEXHEP trial [ 43 ] demonstrated that in samples obtained from patients who underwent cardiac surgery, the presence of DS could lead to a different clinical decision based on the measurement of residual heparin levels after protamine administration, confirming the effect also when UFH is administered in vivo . Finally, this in vitro study was not designed to evaluate clinical outcomes and therefore cannot provide an answer as to whether the performance of the anti-Xa assay in presence of added DS has any clinical impact.…”

Unfractionated heparin: optimizing laboratory monitoring and reducing unwanted interference in everyday hemostasis test practice

“…In particular, some methods in volve dextran sulphate or require an addition of exogenous antithrombin, whereas others do not. In the presence of high concentrations of dextran sulphate, FXa inhibition is much stronger than that predicted from added UFH amounts, 23, 24 which is presumably related to greater availabil ity of UFH for interaction with antithrombin in the assay. As for antithrombin, its inclusion in an antithrombin assay may artificially increase the perceived anti Xa effect, and may not accu rately reflect actual in vivo anticoagulation, es pecially if a patient has reduced antithrombin levels.…”

Thrombosis and Haemostasis 2023 Editors' Choice Papers

“…18 Regular monitoring of anticoagulant activity is crucial for ensuring successful management and safe administration of anticoagulation therapy. A French multicenter study 19 alerted to the significant overestimation of anti-Xa levels in anti-Xa assays using dextran-containing reagents post heparin neutralization by protamine, warranting caution. Adherence plays a pivotal role in the successful management of anticoagulants, significantly influencing effectiveness and treatment outcomes.…”