Should baseline prothrombin time (PT)/international normalized ratio (INR) and activated partial thromboplastin time (aPTT) be obtained in all patients with acute pulmonary embolism?

Baseline PT/INR and aPTT Testing in Acute Pulmonary Embolism

Baseline PT/INR and aPTT are not necessary before initiating anticoagulation in patients with acute pulmonary embolism, as these tests rarely alter initial management and delay life-saving treatment. 1

The Evidence Against Routine Baseline Testing

Key Research Findings

• A retrospective study of 199 patients with deep vein thrombosis or pulmonary embolism found that baseline PT and aPTT values were obtained in 94% of patients, yet heparin therapy was not altered for any patient based on these results 1
• Elevated baseline PT occurred only in patients already taking warfarin, and elevated baseline aPTT was attributed to laboratory error, pre-existing warfarin use, heparin given before testing, anticardiolipin antibodies, or unknown causes—none of which changed acute management 1
• Eliminating routine baseline PT/aPTT testing would result in significant cost savings without compromising patient care 1

Clinical Implications

• Emergency physicians rarely document pertinent questions about bleeding disorders before initiating anticoagulation, making the tests even less useful as screening tools 1
• Baseline coagulation tests are neither sensitive nor specific screening tests for bleeding disorders 1

When Coagulation Tests ARE Needed

For Monitoring Unfractionated Heparin

aPTT monitoring is essential once heparin therapy is initiated, not before 2, 3:

• First aPTT check: 4-6 hours after initial heparin bolus 2, 3
• After any dose change: 6-10 hours later 2, 3
• Once therapeutic: Daily monitoring 2, 3
• Target range: 1.5-2.5 times control value (approximately 45-75 seconds) 2, 3

For Warfarin Therapy

INR monitoring begins after warfarin is started, with target INR of 2.0-3.0 2:

• Initially measured every 1-2 days after starting warfarin 2
• Discontinue heparin after at least 5 days when INR has been ≥2.0 for at least 24 hours 3

The Critical Importance of Early Anticoagulation

Mortality Benefit

Delaying anticoagulation to obtain baseline coagulation tests may increase mortality:

• Patients who received heparin in the emergency department had significantly lower in-hospital mortality (1.4% vs 6.7%, p=0.009) and 30-day mortality (4.4% vs 15.3%, p<0.001) compared to those given heparin after admission 4
• Achieving therapeutic aPTT within 24 hours was associated with lower 30-day mortality (5.6% vs 14.8%, p=0.037) 4
• Early anticoagulation is associated with reduced mortality for acute PE 4

Practical Reality of Achieving Therapeutic Anticoagulation

• Only 19% of patients receiving standard-dose UFH achieve therapeutic aPTT at 12 hours, increasing to only 28.4% at 48 hours 5
• Over half of patients fail to achieve any therapeutic aPTT level within 24 hours of UFH initiation 5
• No patient in one study had all therapeutic aPTT values during the first 48 hours 5

Recommended Approach

Initial Management Algorithm

1. Start weight-adjusted heparin immediately upon diagnosis: 80 IU/kg bolus followed by 18 IU/kg/hour infusion 2, 3
2. Do not delay anticoagulation for baseline PT/aPTT unless there is clear clinical evidence of active bleeding or known coagulopathy 1, 4
3. Obtain first aPTT 4-6 hours after bolus to guide dose adjustments 2, 3

When Baseline Testing May Be Considered

Baseline coagulation tests should only be obtained if:

• Patient has documented history of bleeding disorder 1
• Patient is already on anticoagulation (to guide initial dosing adjustments) 1
• Active bleeding is clinically evident 1

Common Pitfalls to Avoid

• Do not routinely order baseline PT/aPTT as "pretreatment screening"—this delays life-saving therapy without clinical benefit 1, 4
• Do not wait for baseline results before starting heparin—early anticoagulation reduces mortality 4
• Do not confuse baseline testing with monitoring—aPTT is essential for monitoring UFH therapy but not needed before starting it 2, 3
• Consider low molecular weight heparin (LMWH) in stable patients—it has equal efficacy and safety while being easier to use and not requiring aPTT monitoring 3