@inproceedings{8766381,
  abstract     = {{Introduction: The chromogenic anti-Xa activity assay is used for monitoring low molecular weight heparin (LMWH) and unfractionated heparin (UFH). In daily practice, this test is performed shortly after arrival in the lab, and ideally within four hours of blood collection. For research or method validation purposes, stored samples are of value and citrated platelet-poor plasma may be frozen at -80°C for later analysis. Taking into account the limited scientific literature and the potential benefits of a collection of stored samples, we evaluated this pre-analytical factor. According to literature, it is acceptable to freeze samples with LMWH at -80°C for anti-Xa assays, at least for a limited storage time (up to 24 hours). We investigated whether the anti-Xa effect decreases over a longer time in frozen stored samples (several months) containing LMWH or UFH.
Methods: Anti-Xa levels (UFH n=31, LMWH n=30) were compared before and after freezing samples at -80°C for 12–15 months. The STA-Liquid Anti-Xa assay (Diagnostica Stago) was performed on STA Coagulation Analyzers (STA R Evolution® and STA Compact Max®, Diagnostica Stago).
Results: Mean anti-Xa activity for UFH and LMWH before storage was 0.38 IU/mL (range: 0.04–0.73) and 0.42 IU/mL (range: 0.03–1.24), respectively. In samples with UFH, the mean anti-Xa activity after storage (one freeze/thaw cycle) was 0.07 IU/mL (range: -0.17–0.19) lower compared to the original measurement (Figure 1). In samples with LMWH, the mean of the anti-Xa activity after storage was 0.01 IU/mL (range: -0.15–0.11) lower compared to the original measurement (Figure 2). For UFH, 6/31 samples were classified differently in regard of the therapeutic range, of which 4 fell outside and 2 within the therapeutic range after freezing. Pearson’s correlation between the first and second anti-Xa activity measurements was 0.93 for samples with UFH and 0.98 for samples with LMWH.
Conclusions: We observed a minor mean difference in anti-Xa activity after freezing and thawing heparinized samples. We have shown that a freeze-thaw cycle has little effect on sample stability for LMWH, even for a longer storage period. For UFH, we observed in a limited number of samples an influence on clinical interpretation of anti-Xa levels after sample storage for more than one year.}},
  author       = {{Vermeiren, Pauline and Vandevelde, Arne and Devreese, Katrien}},
  booktitle    = {{XXXVth International Symposium on Technical Innovations in Laboratory Hematology, Abstracts}},
  language     = {{eng}},
  location     = {{Bologna, Italy}},
  title        = {{Stability of anti-factor Xa activity after sample storage}},
  year         = {{2022}},
}