Photo by Juan D. Alfonso
ANAHEIM, CA—A new assay can detect and classify direct oral anticoagulants (DOACs) quickly and effectively, according to researchers.
In tests, the assay detected DOACs with greater than 90% sensitivity and specificity.
The assay classified the direct thrombin inhibitor (DTI) dabigatran correctly 100% of the time and classified factor Xa inhibitors (anti-Xa), which included rivaroxaban and apixaban, correctly 92% of the time.
The researchers believe this assay has the potential to be an effective tool for treating patients on DOACs who experience trauma or stroke, as well as those who require emergency/urgent surgery. And the ability to identify the type of anticoagulant a patient is taking can guide the reversal strategy.
Fowzia Zaman, PhD, of Haemonetics Corporation in Rosemont, Illinois, described the assay at the 2015 AABB Annual Meeting (abstract S60-030K). Haemonetics is the company developing the assay, and this research was supported by the company.
About the assay
“The current coagulation assays are not very sensitive to DOACs, especially in the therapeutic range,” Dr Zaman said. “Right now, there is no assay available that can classify the DOACs. This new assay can both detect and classify, and it will classify the DOACs either as a DTI or an anti-Xa.”
The assay is performed using Haemonetics’ TEG 6s system, a fully automated system for evaluating anticoagulation in a patient. It is based on viscoelasticity measurements using resonance frequency and disposable microfluidic cartridges. Each cartridge has 4 channels, and 2 of the channels are used for detection and classification.
Detection is performed using a factor Xa-based reagent, and classification utilizes an Ecarin-based reagent. All of the reagents are contained within the channel, so there is no reagent preparation required.
Each cartridge is loaded into the unit, and citrated whole blood is added, either with a transfer pipette or a syringe, to start the assay.
Reaction time (R-time) is used for detection and classification. R is defined as the time from the start of the sample run to the point of clot formation. It corresponds to an amplitude of 2 mm on the TEG tracing. It represents the initial enzymatic phase of clotting, and it is recorded in minutes.
Study population
The researchers tested the assay in 26 healthy subjects, 25 patients on DTI (all dabigatran), and 40 on anti-Xa therapy (24 on rivaroxaban, 16 on apixaban).
For healthy subjects, the mean age was 41±13, and 46% of subjects are male. Forty-six percent are Caucasian, 39% are African American, and 15% are Asian/“other”. The partial thromboplastin time (PTT) for these subjects was within the normal range, at 27.2±1.8 seconds.
In the DOAC population, the mean age was 68±12 for the anti-Xa group and 69±10 for the DTI group. Fifty percent and 72%, respectively, are male. And 50% and 64%, respectively, are Caucasian.
Most of the patients receiving DOACs were taking them for atrial fibrillation—88% in the anti-Xa group and 84% in the DTI group. Other underlying conditions were coronary artery disease—28% and 32%, respectively—and hypertension—60% and 64%, respectively.
Some patients were taking aspirin in addition to DOACs—30% in the anti-Xa group and 24% in the DTI group. And some were taking P2Y12 inhibitors—20% in the anti-Xa group and 24% in the DTI group.
The PTT was 30.4±4.6 seconds for the anti-Xa group and 36.6±7 seconds for the DTI group. Creatinine levels were 1.07±0.6 mg/dL and 1.05±0.2 mg/dL, respectively.
Assay results
The researchers analyzed citrated whole blood from the healthy volunteers to establish the baseline reference range. The cutoff for detection was 1.95 minutes, and the cutoff for classification was 1.9 minutes.
“What this means is that a person who does not have DOAC in their system should have an R-time of less than or equal to 1.95 minutes,” Dr Zaman explained.
The researchers also developed an algorithm for the detection and classification of DOACs. According to this algorithm, healthy subjects would have a short R-time in the detection channel and the classification channel.
Patients on anti-Xa would have a long R-time in the detection channel but a short R-time in the classification channel. And patients on a DTI would have a long R-time in both the detection channel and the classification channel.
The researchers found that, in the detection channel, on average, R-time was increased 66% for dabigatran, 125% for rivaroxaban, and 100% for apixaban, compared to the reference range. But the degree of elongation was dependent on the individual patient and the time from last DOAC dosage.
Using a cutoff of 2 minutes, the detection channel demonstrated 94% sensitivity and 96% specificity for all the DOACs combined.
“What this means is that, when a patient had a DOAC in their system, the assay was able to pick it up 94% of the time,” Dr Zaman explained.
In addition, the assay detected dabigatran correctly 100% of the time and anti-Xa therapy correctly 92% of the time.
“This TEG 6s DOAC assay is highly sensitive and specific for detecting and classifying DOACs,” Dr Zaman said in closing. “[T]he cutoffs for both the channels are close to 2 minutes, which means clinically relevant results are available within 5 minutes.”
“There is no reagent prep necessary, and it utilizes whole blood, so [there is] no spinning down to plasma. Therefore, it has the potential to be a point-of-care assay.”
