β-Antithrombin, subtype of antithrombin deficiency and the risk of venous thromboembolism in hereditary antithrombin deficiency: A family cohort study

Comparison of antithrombin activity assays in detection of patients with heparin binding site antithrombin deficiency: systematic review and meta-analysis

Antithrombin (AT) deficiency increases the risk for venous thromboembolism, therefore, a highly sensitive assay to identify this condition is crucial. The aim of this paper was to perform a meta-analysis comparing AT activities measured by different AT activity assays in patients with heparin binding site AT deficiency. In addition, the diagnostic sensitivity of selected assays was compared depending on the available data. An extensive literature search was performed considering results with publication date up to July 10, 2021. Seven relevant English-language observational studies, comparing AT activity measured by different AT activity assays in Caucasian Europeans with either the AT Budapest III or AT Padua I mutation were included in meta-analyses. There was no significant difference in AT activity between Labexpert and Innovance in patients with AT Budapest III (P = 0.567) and AT Padua I (P = 0.265), while AT activity determined by HemosIL was significantly higher compared to Innovance for both mutations (AT Budapest III: P < 0.001; AT Padua I: P < 0.001). These results are in line with the results of comparison of diagnostic sensitivity. In patients with AT Budapest III, the AT activity was also higher when measured with Berichrom compared to Innovance (P = 0.002), however, the results of comparison of diagnostic sensitivity across studies were variable. No significant difference (P = 0.117) in AT activity as well as diagnostic sensitivity was observed between Sta-Stachrom and Innovance. The results of our study suggest that Innovance, Labexpert and Sta-Stachrom are the most sensitive activity assays for detection of AT Budapest III and AT Padua I, whereas HemosIL showed considerably lower sensitivity for these two variants. As revealed in our study, the diagnostic sensitivity of AT activity assays to type II heparin binding site AT deficiency is different, and in some assays mutation dependent.

Monitoring of heparins in antithrombin-deficient patients

INTRODUCTION

Heparins exert their anticoagulant effect through activation of antithrombin. Whether antithrombin deficiency leads to clinically relevantly reduced anti-Xa activity of heparins is unknown. We investigated the relation between antithrombin deficiency and anti-Xa activity measurements of plasma samples spiked with unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH).

MATERIALS AND METHODS

Plasma samples from 34 antithrombin-deficient subjects and 17 family controls were spiked with UFH and LMWH (nadroparin) aimed to correspond with an anti-Xa activity of 0.8 IU/mL. Antithrombin, β-antithrombin and anti-Xa activities were measured.

RESULTS

Mean anti-Xa activity with LWMH was 0.55 IU/mL (0.30-0.74) (recovery 69%, 38-93%) in antithrombin-deficient subjects and 0.82 (0.71-0.89) IU/mL in controls (recovery 103%, 89-111%). Expected anti-Xa measurements after LMWH spiking were found in 17/17 non-deficient subjects and in 8/34 antithrombin-deficient subjects. Anti-Xa measurements in the expected range (0.6-1.0 IU/mL) after UFH spiking were found in 17/17 non-deficient subjects and in 1/22 antithrombin-deficient subjects. Antithrombin activity correlated with anti-Xa activity of UFH (R = 0.77) and LMWH (R = 0.66). Mixing studies of pooled normal plasma and antithrombin-deficient plasma showed that anti-Xa recovery was linearly reduced with antithrombin activity decreasing below 100%.

CONCLUSIONS

Reduced antithrombin activity causes significantly reduced anti-Xa levels. Standard LWMH- or UFH-doses are likely to lead to under treatment in antithrombin-deficient individuals.