Renal impairment, bleeding and new/recurrent thrombosis are the most common indications for requesting DOAC levels in hospitalised patients while extremes of BMI and drug interactions are additional reasons in outpatients.

According to a retrospective cohort study conducted at Launceston General Hospital, requests for DOAC levels were increasing.

This is despite “…the convenience of fixed dosing without the need for routine monitoring of drug levels” being one of the selling points for DOACs over warfarin.

The study, published in the Internal Medicine Journal [link here], analysed 129 requests for DOAC measurements from 98 patients at the Launceston General Hospital between January 2017 and December 2022.

Atrial fibrillation was the most common indication for anticoagulation (62%).

Launceston General Hospital did not offer an in-house assay so samples were forwarded to another lab resulting in a turn around time for test results of 1-2 days.

The study found annual requests for DOAC levels increased significantly between 2017 and 2019, remained relatively stable through to 2021 but declined in 2022

“Reasons for this [decline] are unclear but may be because of changes in clinicians’ perspectives over time as new data emerges (e.g. increasing comfort in the use of DOACs in special populations such as renal impairment and obesity),” the study said.

The most common indications for DOAC levels in inpatients were renal impairment (45%), followed by bleeding (33%) and new/recurrent thrombosis (17%).

“For outpatients, the most common indications for DOAC levels were extremes of BMI (32%), followed by renal impairment (16%), new/recurrent thrombosis (13%) and drug interactions (13%).”

However most guidelines do not recommend DOAC levels in the setting of severe renal impairment (with the exception of apixaban) and ISTH guidelines previously reported in the limbic [link here] suggest rivaroxaban or apixaban are appropriate anticoagulant options regardless of high BMI or weight.

Nevertheless, the study found DOAC levels were associated with changes to clinical management in about half the cases overall – anticoagulant cessation (99%), switching to a different anticoagulant (36%), administration of a haemostatic/reversal agent (28%), delay in surgery (7.5%) or dose adjustments (6%).

“In our study, among patients with bleeding (n = 29) who had DOAC levels requested, 66% (n = 19/29) had levels above 50 mmoL/L and haemostatic/reversal agents were given in 45% (n = 13/29),” the investigators said.

Haematologists Dr Ming Lim and Associate Professor Muhajir Mohamed noted a significant number of requests for DOAC levels were incorrect or incomplete, for example omitting time from last dose and DOAC dose/frequency.

“This highlights the need for the education of clinicians regarding the adequacy of request information to ensure the performance of the correct test, the accurate interpretation of results and the timely availability of results without unnecessary delay.”

They also said the demand for DOAC levels was expected to increase as specific reversal agents such as andexanet alfa or idarucizumab become increasingly available in many centres.

“Future prospective studies investigating the clinical utility of DOAC levels in specific clinical settings, such as prior to surgery or administration of reversal/ haemostatic agents in acute major bleeding, are urgently needed,” they concluded.