Coagulation

DOAC neutraliser prevents misleading coag results


Evidence is building for the utility of DOAC Stop to neutralise the effects of the direct-acting oral anticoagulants (DOACs) on laboratory tests such as prothrombin time (PT) and factor VIII assays.

A UK study of plasma samples from 40 DOAC anticoagulated patients and 20 patients who were not anticoagulated showed that the Australian-made product DOAC Stop largely removed the anti-Xa drugs and their interfering effects on coagulation tests.

Patient samples were analysed before and after treatment with a DOAC Stop tablet.

The study found PT, activated partial thromboplastin time (APTT), factor VIII levels and dilute Russell’s viper venom time (DRVVT) normalised in most samples after the addition of DOAC Stop.

The findings, consistent with another study, suggest DOAC Stop can help reduce the possibility of labs reporting false positive coagulation tests and doctors misinterpreting the reported information.

As an example: “Before treatment with DOAC Stop, 13 out of 20 samples from patients on rivaroxaban had a percentage correction of the DRVVT above 10% that would be [falsely] interpreted as lupus anticoagulant positive, but only two of those 13 remained positive after treatment,” the study said.

There was no difference between the coagulation tests of untreated and treated samples from control patients.

Dr Emmanuel Favaloro, principal scientist in haemostasis at Westmead Hospital’s Institute of Clinical Pathology and Medical Research, a part of NSW Health Pathology, told the limbic his experience with DOAC Stop was also positive.

“The way it usually works is you do the coagulation test and if you get an unexpected abnormal result suggestive of DOAC interference then you repeat the test after treatment with DOAC Stop. And if you get a normal result then that suggests the original abnormal results were indeed due to DOAC interference.”

However, there was some potential resistance to labs using it routinely for a number of reasons.

“We don’t know necessarily when a patient is on a DOAC and therefore don’t always know when to use it.”

“There also may be a hesitation in that it requires purchasing DOAC Stop, plus an extra treatment step and additional testing, all of which costs the lab money, for which they won’t get reimbursed.”

And there are perceived quality assurance issues when NATA accredited laboratories using TGA-listed reagents ‘start fiddling’ with tests outside the manufacturer’s instructions.

“Because of those issues, it currently remains more of a research tool. In our own experience it works well but we’re still grappling with these issues before we can officially use it in the lab environment for diagnostics.”

He said ideally, after years of experience with DOACs, manufacturers would start providing reagents that incorporate a DOAC neutraliser as already happens for heparin.

“And they are probably working towards that,” he said.

Commenting on the UK study’s observation that complete reversal of anti-Xa activity did not occur in every sample, Dr Favaloro said even incomplete reversal may be sufficient to neutralise the effect of DOACs on coagulation tests.

“We haven’t got enough information yet, but there have been a couple of reports to suggest that when the level of the DOAC is above the level that one usually sees in patients on therapy, sometime there is incomplete reversal.”

He said DOAC plasma levels under 100 ng/mL don’t always affect coagulation tests enough to generate abnormal test results, so even an incomplete reversal from much higher levels might still be useful.

“DOAC Stop may not completely reverse the anti-Xa in all cases but it may reverse the false positives. I think it’s a big step in the right direction.”

He added the product neutralised all of the commonly used DOACs and was relatively inexpensive compared to in vivo agents such as idarucizumab.

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