PB1153 - Shortening of APTT when Heparin Neutralising Calcium Solution Replaces Calcium Alone is Highly Specific for the Presence of Heparin.

Background: Identifying the cause of a prolonged APTT is often required for safe patient management. Unfractionated heparin can prolong APTT, but samples may not be identified as containing heparin so a simple method to confirm presence of heparin may be useful to avoid more expensive and time consuming additional testing. Heparin resistant re-calcifying solution (HRRS) can reportedly be substituted for regular calcium chloride in APTT to eliminate UFH up to 1 IU/ml.

Aims: To assess HRRS as replacement for 25 mM calcium chloride in APTT

Methods: Plasma was prepared from samples collected into 0.109M trisodium citrate (Vacutainer Plus, Becton Dickinson) by single or double (samples containing heparin) centrifugation at 2000g for 10 mins followed by storage at -70oC. APTTs were performed using Actin FS and Synthasil on the Sysmex CS5100 analyser in varying patient groups (table1 and 2) using both HRRS and 25mM calcium chloride.

Results: HHRS successfully neutralised UFH in all 20 samples containing anti Xa up to 0.9 IU/ml. The percentage shortening, ranging from 11% to 83%, was similar for both reagents and was greater at higher heparin levels. APTTs in the presence of 3 types of LMWH shortened by up to 10% on average (Table 1) with several individual samples showing an APTT shortening of 10-30%. APTTs of other patient groups including patients on direct Xa inhibitors increased on average by up to 10% (Table 2) and no individual sample showing a shortening of more than 5%.

Conclusion(s): HHRS successfully neutralised UFH up to at least 0.91 IU/ml. APTTs of non UFH samples increased by up to 10% on average, with no individual sample showing a shortening of >5%, confirming that shortening of >10% is highly specific for heparin. A shortening of APTT of 10-30 % indicated heparin of some sort was present, with shortening of >30% only observed for UFH.