What are the recommended hypercoagulable labs for inpatients already on Heparin (unfractionated heparin)?

From the Guidelines

For inpatients already on heparin who require hypercoagulable workup, I recommend obtaining protein C activity, protein S activity, antithrombin III activity, factor V Leiden mutation, prothrombin gene mutation (G20210A), lupus anticoagulant, anticardiolipin antibodies, beta-2 glycoprotein antibodies, homocysteine levels, and JAK2 mutation testing. Since the patient is already on heparin, certain tests like protein C, protein S, and antithrombin III will be affected and may show falsely low results 1. Therefore, these tests should ideally be collected before starting anticoagulation or at least 2 weeks after discontinuation. However, genetic tests like factor V Leiden and prothrombin gene mutation are not affected by anticoagulation and can be performed at any time. For lupus anticoagulant testing, heparin can interfere with results, so samples should be drawn when the patient is at trough heparin levels or use special laboratory techniques to neutralize heparin.

Some key points to consider when interpreting these results include:

• Acute thrombosis itself can temporarily decrease protein C, protein S, and antithrombin III levels 1
• Heparin can interfere with lupus anticoagulant testing, so special considerations are needed 1
• Genetic tests are not affected by anticoagulation and can be performed at any time
• It's essential to interpret these results in clinical context and consider repeating abnormal tests after resolution of the acute event and discontinuation of anticoagulation to confirm true deficiencies versus transient changes. The management of heparin-induced thrombocytopenia (HIT) is also crucial, and guidelines suggest monitoring platelet counts every 2 or 3 days from day 4 to day 14 in patients at high risk of HIT 1.

From the FDA Drug Label

When initiating treatment with Heparin Sodium Injection by continuous intravenous infusion, determine the coagulation status (aPTT, INR, platelet count) at baseline and continue to follow aPTT approximately every 4 hours and then at appropriate intervals thereafter Dosage is considered adequate when the activated partial thromboplastin time (aPTT) is 1.5 to 2 times normal or when the whole blood clotting time is elevated approximately 2. 5 to 3 times the control value. Periodically monitor platelet counts, hematocrit, and occult blood in stool during the entire course of heparin therapy, regardless of the route of administration.

The recommended hypercoagulable labs for inpatients already on heparin include:

• Activated Partial Thromboplastin Time (aPTT): to be checked approximately every 4 hours and then at appropriate intervals thereafter
• International Normalized Ratio (INR): to be checked at baseline
• Platelet count: to be checked periodically during the entire course of heparin therapy
• Hematocrit: to be checked periodically during the entire course of heparin therapy
• Occult blood in stool: to be checked periodically during the entire course of heparin therapy 2

From the Research

Hypercoagulable Labs for Inpatients on Heparin

• The following labs are recommended for inpatients on heparin:
  • Activated partial thromboplastin time (APTT) 3, 4, 5
  • Anti-Xa activity assay 5
  • Prothrombin time (PT) 6, 7
  • Antithrombin 3, 5, 7
  • Fibrinogen 5, 7
  • D-Dimer 5, 7
  • Factor VIII 5
  • von Willebrand Factor 5

Considerations for Lab Results

• APTT results may not accurately reflect heparin levels in patients with elevated fibrinogen, FVIII, or lupus anticoagulant 5
• Anti-Xa activity assay may be a more reliable method for monitoring heparin treatment than APTT in acute patients 5
• PT results should be reported as international normalized ratio (INR) for patients on vitamin K antagonists, but this may not be valid for patients on heparin 6
• Storage of whole blood at ambient temperature for up to 8 hours does not significantly affect coagulation parameters, but storage for 24 hours may affect APTT results 7