March 2023

Measuring Emicizumab

For those laboratory scientists who are likely to come across patients being treated with the new factor VIII replacement agent emicizumab, there are a few important considerations in testing.  Chromogenic factor VIII assay kits based on bovine FIXa and FX have been widely promoted as being useful in such patients. Jean Amiral at Hyphen BioMed pioneered their use. However, these do not measure emicizumab. They measure only “real” or natural factor VIII activity. The bifunctional antibody emicizumab requires human FIXa and FX epitopes to connect and express FVIII-like activity.  

Chromogenic factor VIII kits containing human FIXa and FX (as well as functional clotting assays), measure both natural FVIII and emicizumab. Thus, to measure emicizumab specifically it is necessary to have both methods available. This is particularly important to consider in patients being tested for inhibitors to FVIII. We are grateful to Geoff Kershaw at RPA Hospital, Sydney for expert advice on the Hyphen BioMed kits.

Some advantage for mechanical clot timers with DOAC-Stop™?

Some users of DOAC-Stop™ in the UK recently expressed concern about residual black carbon particles in plasmas after centrifugation and what effect they may have on clotting test results. This is more of a problem with microfuges where the sediment is deposited along the wall of the tube rather than pelleted on the bottom as with swing out tubes.  

We investigated this potential problem recently at Haematex. We prepared plasmas containing variable amounts of DOAC-Stop™ without centrifuging and tested them directly in our ST4 machine. To our surprise the presence of DOAC-Stop™ had no effect whatever on clotting times in various tests and in a range of test plasmas. Even at the highest concentration, with DOAC-Stop™ at 1 minitablet per 1ml plasma uncentrifuged the totally black suspensions gave the same clotting time results as the initial plasmas. Of course, this was because we were using a Stago ST4 magnetic ball-based clotting instrument. The activated charcoal particles did not affect the motion of the stirrer balls and turbidity did not influence results from a range of plasmas and in various tests including APTT, PT and dRVVTs. It is likely that residual activated charcoal may affect photo-optical clotting instruments and users should take care. We would be grateful for any lab to report on such interference.

However, DOAC-Stop™  can be used directly in samples and without centrifugation when clot detection is by physical or viscoelastic testing. DOAC-Stop™  has already been used successfully to remove apixaban from whole blood samples in ROTEM viscoelastic studies. Preliminary tests on the ClotPro with Tony Ghent (Haemoview) have also shown that DOAC-Stop™ works to remove DOACs in samples without requiring centrifugation. The current DOAC-Stop™ minitablets cause some slight haemolysis and platelet activation in whole blood which should be avoided.  

Tea with Tom

Episode 8, Tom talks about a new laboratory diagnostic test for DOACs called GO-DOAC™ Test. https://youtu.be/StGmu0GGqE0

Haematex is the only Australian distributor which carries out local R&D into coagulation diagnostics. When you purchase from us, a portion of profits go towards projects such as our own locally made DOAC-Stop™, and research on dRVVT and lupus anticoagulants.

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