Clinical Evaluation for Blood Clots (Venous Thromboembolism)
Immediate Risk Stratification and Clinical Probability Assessment
Begin by assessing clinical probability using validated criteria that include major risk factors and the likelihood of alternative diagnoses, then immediately initiate anticoagulation in intermediate or high probability cases without waiting for imaging confirmation. 1, 2
Clinical Probability Scoring
Assign points based on the following criteria 1:
Major risk factors present (+1 point each):
Alternative diagnoses unlikely (+1 point): 1
Hemodynamic Assessment for Pulmonary Embolism
Massive (high-risk) PE is defined by systolic blood pressure <90 mmHg, shock, or cardiac arrest with collapse, unexplained hypoxia, and engorged neck veins. 2, 3 This distinction is critical as it determines whether thrombolysis is indicated immediately 1, 3.
Immediate Anticoagulation Protocol
When to Start Anticoagulation BEFORE Imaging
- High clinical probability: Start parenteral anticoagulation immediately while awaiting diagnostic tests 1, 3
- Intermediate clinical probability: Start anticoagulation if imaging will be delayed >4 hours 1
- Low clinical probability: Withhold anticoagulation if test results expected within 24 hours 1
Choice of Initial Anticoagulant
For hemodynamically stable patients (non-massive PE or DVT), low molecular weight heparin (LMWH) is preferred over unfractionated heparin due to equal efficacy, superior safety profile, and ease of use. 1, 3
Specific dosing:
- LMWH (enoxaparin): 1 mg/kg subcutaneously twice daily OR 1.5 mg/kg once daily 3
- Fondaparinux: Weight-based dosing (alternative to LMWH) 1
Use unfractionated heparin (UFH) in these specific scenarios: 1, 3
- Massive PE with hemodynamic instability 3
- High bleeding risk requiring rapid reversibility 1
- Severe renal dysfunction (creatinine clearance <30 mL/min) 3
- Extreme obesity 3
- Thrombolysis being considered 1
UFH dosing when indicated: 1, 2
- Initial bolus: 80 IU/kg IV 2
- Maintenance infusion: 18 IU/kg/hour 2
- Target aPTT: 1.5-2.5 times control (45-75 seconds) 1, 2
Critical monitoring for UFH: 1, 2
- First aPTT check: 4-6 hours after initial bolus 1, 2
- After dose adjustments: 6-10 hours later 1
- Once therapeutic: Daily 1, 2
Contraindications to Heparin
Absolute contraindications: 3
Relative contraindications requiring careful risk-benefit assessment: 3
D-Dimer Testing Strategy
D-dimer should ONLY be used in low or intermediate clinical probability patients—never order it in high probability cases. 1
- Low clinical probability: Negative D-dimer (SimpliRED, Vidas, or MDA assays) reliably excludes PE; no imaging needed 1
- Intermediate clinical probability: Negative D-dimer (Vidas or MDA assays only) excludes PE 1
- High clinical probability: Skip D-dimer entirely and proceed directly to imaging 1
Diagnostic Imaging Protocol
For Non-Massive PE
CT pulmonary angiography (CTPA) is the recommended initial imaging modality. 1, 3 A good quality negative CTPA reliably excludes PE and requires no further investigation or treatment 1.
Timing requirements: 1
For Suspected DVT
In patients with clinical signs of DVT, leg ultrasound can confirm VTE without lung imaging. 1 However, a single normal ultrasound does not exclude subclinical DVT 1.
For Massive PE
CTPA or echocardiography will reliably diagnose massive PE. 1 Echocardiography showing right ventricular dysfunction supports the diagnosis 1.
Management of Massive (High-Risk) PE
Thrombolysis is first-line treatment for massive PE and may be instituted on clinical grounds alone if cardiac arrest is imminent. 1, 2, 3
Recommended thrombolytic regimen: 1, 2, 3
Other thrombolytic options: 1, 2
- Streptokinase: 250,000 units over 20 minutes, then 100,000 units/hour for 24 hours (plus hydrocortisone to prevent circulatory instability) 1, 2
- Urokinase: 4,400 IU/kg over 10 minutes, then 4,400 IU/kg/hour for 12 hours 1, 2
Stop heparin before thrombolysis; resume maintenance dose afterward. 1, 2
Transition to Oral Anticoagulation
Start warfarin only AFTER VTE is confirmed on imaging, on the same day as parenteral therapy begins. 1
Warfarin protocol: 1
- Initial dose: 5-10 mg daily for 2 days 1
- Target INR: 2.0-3.0 1
- Continue parenteral anticoagulation for minimum 5 days AND until INR ≥2.0 for at least 24 hours 1
- Monitor INR every 1-2 days initially 1
Duration of Anticoagulation
The duration depends on the clinical scenario: 1, 2
- Temporary risk factors (surgery, trauma): 4-6 weeks to 3 months 1, 2
- First idiopathic VTE: Minimum 3 months 1, 2
- Recurrent VTE or persistent risk factors: At least 6 months, consider indefinite therapy 1, 2
Critical Monitoring and Safety Considerations
Thrombocytopenia Surveillance
Monitor platelet counts at baseline and periodically during heparin therapy to detect heparin-induced thrombocytopenia (HIT). 4 If platelets fall below 100,000/mm³ or recurrent thrombosis develops, immediately discontinue heparin and consider alternative anticoagulation 4.
HIT can occur up to several weeks AFTER discontinuing heparin. 4 Patients presenting with thrombocytopenia or new thrombosis after stopping heparin require evaluation for delayed HIT 4.
Hemorrhage Monitoring
An unexplained fall in hematocrit, drop in blood pressure, or any unexplained symptom should trigger immediate consideration of hemorrhagic complication. 4 If bleeding occurs, discontinue heparin and consider protamine sulfate reversal 4.
Common Pitfalls to Avoid
- Never delay anticoagulation in intermediate or high probability patients while awaiting imaging 1, 3
- Never use D-dimer in high clinical probability patients—it wastes time and resources 1
- Never start warfarin before VTE is confirmed on imaging 1, 3
- Never use thrombolysis as first-line treatment for non-massive PE 1
- Never forget to monitor platelets during heparin therapy—HIT is serious and potentially fatal 4