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Guidance for Laboratory Testing for Patients on DOAC

This Guidance is provided in conjunction with Trust Document. Download WHAT-HAE-002 Oral Anticoagulants –Guidelines & Procedures

The use of DOAC’s does not require any routine coagulation monitoring however in some clinical situations tests can help clinical decision making and assist patient management. There are assays available for both qualitative and quantitative measurement of DOAC‘s in the form of fast turnaround screening tests and assessment of drug plasma levels (longer turnaround times).

When requesting any coagulation tests for patients receiving DOAC treatment it is important to provide the clinical status, including renal & hepatic function together with time of administration of last dose. Impaired renal and hepatic function influences DOAC exposure levels due to the complexity of metabolism and elimination.

A fast turnaround may be provided by performing either a PT or APTT assay as these are readily available and suitable for some DOAC’s.

The current methodology in the laboratory utilises reagents which are recognised as sensitive for these tests and therefore normal test results (within reference range) infer acceptable levels.

Tests currently utilised are:

• PT Assay for Rivaroxaban
• APTT Assay for Dabigatran

The anticoagulation effects of Apixaban cannot be measured using either of these assays and therefore if either a PT and/or APTT assay is requested for patients on Apixaban a normal test result does not infer acceptable levels. No routine coagulation test can reliably measure the anticoagulant effect.

Please note: Point-of-Care testing (Coaguchek) is also not recommended for the measuring the anticoagulation effects of DOAC’s.

Anti-Factor Xa assay is also available for quantitation of Rivaroxaban, Apixaban & Edoxaban and a Diluted Thrombin Time is available for Dabigatran.

Clinical evidence and patient risk factors should always be considered when making clinical decisions on increased bleeding risks. Thrombophilia testing should not be performed on patients receiving DOAC treatment due to the potential influence on coagulation function.

Emergency situations / life-threatening bleeding

Please ring Ext 39617 (WRH) or 42082 (Alex)  (08:00 – 20:00) in advance of sending samples to notify the laboratory of any urgent requests. Outside of routine hours please contact Switchboard to bleep the Haematology Laboratory BMS.

First line tests

 It is unlikely that the bleeding event is enhanced by Rivaroxaban or Dabigatran if the result for the first line test above is normal.

Qunatitation

The plasma drug levels can also be quantitated, depending on the urgency of the situation. If time is critical it may not be possible to provide results for these tests due to the increased turnaround time. These requests are sent to a referral laboratory with a turnaround time of up to 4hrs.

All laboratory results should however be interpreted with caution as the clinical significance of elevated results remains unclear.

Patients without bleeding – screening tests elevated

Quantitative tests to determine plasma levels of DOAC may be performed if initial screening tests (PT or APTT if relevant) are raised and indicate a risk of bleeding.

Quantitation

Patients with suspected VTE

Laboratory testing is of clinical value if a thrombotic event occurs but quantitative tests are more appropriate (see table above). Potential drug interactions should be checked if the drug level is lower than that expected.

Prior to surgical procedures

Laboratory testing is not necessary for these patients if DOAC abstention guidelines are followed correctly.

The measurement of plasma drug levels may be helpful for high risk patients undergoing neurological, cardiac or vascular surgery.

Screening tests may be used if the effects of reversal agents are required and quantitative plasma levels measured if extent of reversal is required. (See relevant tables above).

Suspected overdose

Quantitative assays can be used to assess exposure levels and to determine the time before next dose (see table above).

Please contact the Coagulation Laboratory on 39617 (WRH) or 42082 (Alex) (08:00 – 20:00) or bleep the Haematology BMS on relevant site if you require any further advice.

References

Practical Guidance on the Use of Laboratory Testing in the Management of Bleeding in Patients Receiving Direct Oral Anticoagulants
Hugo ten Cate, Yvonne MC Henskens, Marcus D Lance
Vasc Health Risk Manag 2017; 13:457-467