PB0491 Patients from Different Settings Receiving Unfractionated Heparin (DEXHEP Study): Impact of PF4 on Anti-Xa Levels
Résumé
Background: In the DEXHEP study including 165 patients receiving
unfractionated heparin (UFH), we reported that anti-Xa levels were higher
when using a reagent containing dextran sulphate (DS) versus no DS. DS
dissociates UFH/neutralizing protein (such as PF4) complexes. However, the
impact of PF4 on the variability of anti-Xa levels measured with or without
DS and using CTAD or citrate collection tubes is not known.
Aims: To measure PF4 concentrations in citrate and CTAD samples from
patients in different clinical settings receiving UFH and to assess the
association between anti-Xa and PF4 levels.
Methods: Blood was collected into citrated and CTAD tubes in four groups
of patients. Anti-Xa assays were performed with seven assay/analyser
combinations. PF4 levels were measured with ZymutestTM PF4 (Hyphen-
Biomed) kit.
Results: Citrated and CTAD samples from 144 patients were analysed. PF4
levels were higher in citrated samples (+351% [+301;+406], p < 0.0001)
(Figure1), despite short preanalytical time-periods (88% of blood centrifuged
within 2 h). Pneumatic transportation increased PF4 levels, with a greater
effect in CTAD tubes (+87%, p < 0.0001) than in citrated tubes (+32%,
p = 0.003). However, its effect on anti-Xa levels is less stringent and depends
on the patients group. In CTAD samples, anti-Xa levels were higher (+15%,
p = 0.005) than in citrated samples. The difference of anti-Xa levels between
citrate and CTAD tended to be higher when the differences of PF4
concentrations increased (beyond around 200 ng/mL) (Figure2). The
difference was observed with all commercially available reagents used
regardless the presence or not of DS
Conclusion(s): CTAD minimizes but might not be sufficient to fully prevent
ex-vivo PF4 release. The PF4 release is increased by pneumatic transpor-
tation. The presence of PF4 may affect anti-Xa levels but does not totally
explain the differences of anti-Xa levels observed with or without DS. The
reason for higher anti-Xa levels obtained with DS reagents still needs further explorations