What labs are required prior to starting a Direct Oral Anticoagulant (DOAC)?

From the Guidelines

Before starting a Direct Oral Anticoagulant (DOAC), laboratory tests such as a complete blood count (CBC), comprehensive metabolic panel (CMP) with liver function tests, serum creatinine with calculated creatinine clearance, and coagulation studies like PT/INR should be performed. These baseline assessments are crucial for proper DOAC selection and dosing, as emphasized by the 2013 recommendation from the subcommittee on control of anticoagulation of the scientific and standardisation committee of the international society on thrombosis and haemostasis 1. The CBC helps identify any pre-existing anemia or thrombocytopenia that might increase bleeding risk. Liver function tests are important because DOACs undergo hepatic metabolism, and dosing adjustments may be needed in liver impairment. Renal function assessment is critical since DOACs are partially eliminated by the kidneys, with specific dose adjustments required based on creatinine clearance values, particularly for patients with moderate to severe renal impairment.

Key Laboratory Tests

• Complete Blood Count (CBC) to identify pre-existing anemia or thrombocytopenia
• Comprehensive Metabolic Panel (CMP) with liver function tests to assess hepatic metabolism and potential need for dosing adjustments
• Serum creatinine with calculated creatinine clearance to determine renal function and guide dose adjustments
• Coagulation studies such as PT/INR to provide a baseline for future comparisons in case of bleeding complications

The most recent guideline from 2023 suggests the measurement of plasma levels of oral direct antifactor Xa agents such as apixaban, edoxaban, or rivaroxaban in patients treated or suspected of being treated with one of these agents 1. However, this recommendation is more relevant to the management of bleeding and coagulopathy following trauma rather than the initial assessment prior to starting a DOAC.

Considerations for Specific Patient Groups

• For female patients of childbearing age, a pregnancy test should be considered as DOACs are contraindicated during pregnancy.
• Patients with moderate renal insufficiency and moderate liver function impairment require special caution, with potential dose reduction of the NOAC according to the specific drug label 1.

In clinical practice, the selection and assessment of patients treated with DOACs must be guided by a thorough evaluation of patient characteristics, including age, body weight, history of renal or liver disease, history of bleeding, other co-morbidities, and use of concomitant drugs 1. This approach ensures the safe and effective use of DOACs, minimizing the risk of adverse outcomes such as bleeding complications.

From the Research

Labs Required Prior to Starting DOAC

The following labs are required prior to starting a Direct Oral Anticoagulant (DOAC):

• Renal function tests, including estimated glomerular filtration rate (eGFR) to assess kidney function 2, 3
• Activated partial thromboplastin time (APTT) and/or thrombin time (TT) for dabigatran 4
• Prothrombin time (PT) for rivaroxaban, although this is not endorsed by all guidelines 4
• Anti-FXa assay for rivaroxaban and apixaban 4
• Ecarin clot time (ECT) or dilute TT/direct thrombin inhibitor assay (Hemoclot thrombin inhibitor) for dabigatran 4

Special Considerations

• Patients with chronic kidney disease (CKD) require careful monitoring of renal function before initiation and after start of DOAC 2, 3
• Patients with severe renal impairment or end-stage renal disease (ESRD) may not be suitable for DOAC therapy 2, 3
• Elderly patients and those with impaired renal function may require therapeutic drug monitoring with DOACs to predict bleeding events 5
• Measuring DOAC levels before surgery or invasive procedures may be important for patient safety, especially in patients with renal impairment or those taking concomitant medications 6