haemofiltration and APTT, can i ask......

We are about to start training on Prisma flex by Gambro.
These machines do not have a needle free system for sampling blood for APTT, we have to use a needle and syringe. This is a practice that we are desperate to avoid/stop using.
We could sample from the A-Line, however there is a marked difference between the results given from a sample taken from an A-Line and that of a circiut sample.
We are interested in heparinisation of the circuit and not the patient.
How do you do this in your depts?
I am a bit stuck with this problem, and i am very interested in how the rest of the world do this.
Many thanks,
Dissle x