Pre-Anticoagulation Assessment Checklist
Before initiating anticoagulant therapy, you must obtain laboratory tests (complete blood count, PT/aPTT, serum creatinine with calculated creatinine clearance, liver function tests including transaminases and bilirubin), assess bleeding risk factors, review all concomitant medications for drug interactions, and evaluate patient-specific characteristics including age, weight, renal function, and hepatic function 1.
Essential Laboratory Tests
Obtain the following baseline labs before prescribing any anticoagulant:
- Complete blood count - to establish baseline hemoglobin and platelet count
- PT and aPTT - baseline coagulation parameters
- Serum creatinine with calculated CrCl - use Cockcroft-Gault or MDRD formula; this is mandatory, not optional 1
- Liver function tests - transaminases and bilirubin to assess hepatic function 1
Patient Characteristic Assessment
Evaluate these specific factors that directly impact anticoagulant selection and dosing:
- Age - elderly patients require lower warfarin doses and may need DOAC dose adjustments 1, 2
- Body weight - extremes of weight affect drug distribution and clearance 1
- Renal function - DOACs are contraindicated or require dose reduction with severe renal impairment; calculate CrCl, don't just look at creatinine 1
- Hepatic function - moderate-to-severe liver disease requires special caution or contraindication 1
- History of bleeding - prior gastrointestinal bleeding, intracranial hemorrhage, or other major bleeding events 1
Drug Interaction Review
Carefully review all concomitant medications before prescribing, as drug interactions are a major cause of anticoagulant-related complications 1:
For DOACs (Dabigatran, Rivaroxaban, Apixaban):
Contraindicated combinations:
- Dabigatran with: ciclosporin, itraconazole, ketoconazole, tacrolimus 1
- Rivaroxaban with: azole antimycotics, HIV protease inhibitors (strong dual CYP3A4 and P-gp inhibitors) 1
Require dose adjustment or extreme caution:
- P-gp inhibitors with dabigatran: amiodarone, verapamil, quinidine, clarithromycin 1
- CYP3A4/P-gp inhibitors with rivaroxaban: clarithromycin, erythromycin 1
- CYP3A4 inducers (reduce efficacy): phenytoin, carbamazepine, phenobarbital, rifampicin 1
Antiplatelet Agents:
Concomitant aspirin or other antiplatelet drugs increase bleeding risk substantially - document the necessity and reassess whether combined therapy is truly required 1
Bleeding Risk Assessment
Perform a validated bleeding risk assessment such as HAS-BLED at baseline 3. This is not just a box to check - it should guide your decision-making and identify modifiable risk factors.
Key bleeding risk factors to document:
- Uncontrolled hypertension (modifiable)
- Prior major bleeding
- Thrombocytopenia or coagulopathy
- Concurrent antiplatelet use
- Alcohol abuse (modifiable)
- Labile INR history (if previously on warfarin)
Special Considerations for Warfarin
If initiating warfarin specifically:
- Parenteral anticoagulation overlap - continue heparin/LMWH for minimum 5 days AND until INR ≥2.0 for at least 24 hours 4
- Dietary vitamin K assessment - counsel on consistent vitamin K intake, not avoidance 2
- Baseline INR - must be obtained before first dose 1
Common Pitfalls to Avoid
Failing to calculate CrCl - looking at serum creatinine alone misses renal impairment, especially in elderly patients with low muscle mass 1
Missing drug interactions - not reviewing the medication list for P-gp inhibitors or CYP3A4 inducers/inhibitors leads to under- or over-anticoagulation 1
Inadequate patient education - patients must understand the bleeding risk, when to seek help, and the importance of adherence before leaving your office 1, 4
Starting warfarin without parenteral overlap - this creates a transient hypercoagulable state due to rapid protein C depletion 4