RESUMO
Current guidelines recommend performing laboratory tests aimed at monitoring unfractionated heparin (UFH) treatments within a delay not exceeding 1 to 2â¯h(s) after sampling when blood is collected into citrated tubes. As such a short delay could be an issue, we evaluated the potential impact of longer delays. For that purpose, two citrated tubes were obtained from patients on UFH: one was centrifuged and tested for anti-Xa activity and aPTT within 1â¯h after collection (T1â¯h) and one was stored for 4â¯h at room temperature (T4â¯h) before being processed. A total of 123 paired tubes were investigated. Anti-Xa activity was significantly lower at T4â¯h than at T1â¯h, with a mean bias, calculated according to Bland-Altman, of 0.05â¯IU/mL. Considering 0.30 to 0.70â¯IU/mL as the therapeutic range, there were 12 cases of discrepant test results (9.8%). Most of them being around the lower limit of the therapeutic range had no impact on patients' management. APTT was significantly shortened (pâ¯<â¯0.0001) at T4â¯h vs. T1â¯h, with a mean bias of -7.9â¯s. Considering anti-Xa correlated aPTT therapeutic range, 29 cases of discrepant test results (23.6%) were found, 10% would have induce dosage changes. The concordance between anti-Xa activities measured at T4â¯h and T1â¯h was excellent (kappaâ¯=â¯0.813) and good for aPTT (kappaâ¯=â¯0.661). In conclusion, extending the delay between blood collection and measurement of tests prescribed for monitoring UFH therapy up to 4â¯h was found to lead to a systematic reduction in both anti-Xa activity and aPTT in unspun citrated tubes. As changes at T4â¯h were limited and had few clinically relevance than the ones observed with aPTT testing, a 4â¯h-delay was found to be acceptable for anti-Xa activity. The maximum delay for aPTT should remain around 1-2â¯h as changes were more relevant.