From the Guidelines
For inpatients with suspected hypercoagulable states, I recommend ordering a comprehensive panel that includes PT/INR, PTT, and D-dimer as baseline coagulation parameters, as well as viscoelastic coagulation tests such as thromboelastography (TEG) or rotational thromboelastometry (ROTEM) to rapidly detect coagulation disorders. The choice of tests should be guided by the clinical context and the specific anticoagulant therapy the patient is receiving 1. For patients on warfarin, PT/INR is the most appropriate test, while for patients on heparin, PTT or anti-Xa activity should be used 1. For patients on direct oral anticoagulants (DOACs), viscoelastic coagulation tests such as TEG or ROTEM may be more useful in detecting coagulopathy 1.
Some key points to consider when interpreting these tests include:
- PT/INR is sensitive to warfarin but not to DOACs, and its results should not be interpreted as INR in patients treated with DOACs 1
- PTT is sensitive to heparin and dabigatran, but its results can be affected by various factors such as standardizing the reagents used, lack of correct synthesis of coagulation factors, consumption of coagulation factors in active bleeding or thrombosis, and liver or hematological disorders increasing baseline aPTT 1
- Viscoelastic coagulation tests such as TEG or ROTEM can provide rapid detection of coagulation disorders and are useful in guiding reversal therapies 1
- The results of these tests should be interpreted in the context of the patient's clinical presentation and the specific anticoagulant therapy they are receiving 1
It's also important to note that the timing of these tests is crucial, and ideally, samples should be collected before initiating anticoagulation therapy, as heparin and warfarin can affect the results of protein C, protein S, and antithrombin III assays 1. If the patient is already anticoagulated, results should be interpreted cautiously and consideration should be given to repeating tests after therapy completion 1.
From the FDA Drug Label
Adjust the dosage of Heparin Sodium Injection according to the patient's coagulation test results. 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. 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 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 include:
- Activated partial thromboplastin time (aPTT): to be monitored approximately every 4 hours when initiating treatment with heparin by continuous intravenous infusion
- International normalized ratio (INR): to be determined at baseline when initiating treatment with heparin by continuous intravenous infusion
- Platelet count: to be monitored periodically during the entire course of heparin therapy
- Hematocrit: to be monitored periodically during the entire course of heparin therapy
- Occult blood in stool: to be monitored periodically during the entire course of heparin therapy 2
From the Research
Hypercoagulable Labs for Inpatients
The following are recommended hypercoagulable labs for inpatients:
- Activated protein C resistance/factor V Leiden 3
- Prothrombin G20210A 3
- Deficiencies of protein C, protein S or antithrombin 3
- Antiphospholipid antibodies 3
- Prothrombin time (PT) 4
- Activated partial thromboplastin time (aPTT) 4
- Thromboelastography (TEG) 4
- D-dimer 4, 5
- Protein C percent activity 4
- Antithrombin III percent activity 4
- Endogenous thrombin potential (ETP) with and without thrombomodulin 5
- Coagulation factors (I, II, V, VII, VIII, IX, X, XI, and XII) 5
- Von Willebrand factor (vWF) antigen 5
- Clot lysis time 5
- Prothrombin fragment F1+2 5
- Activated factor VII 5
- Plasmin-antiplasmin complex 5
Laboratory Testing Considerations
Laboratory testing for hypercoagulability should be considered in patients with clotting and underlying risk factors, such as malignancy, pregnancy, estrogens, or surgery 6. Individuals are best tested when they are not taking anticoagulants 6. The detection of one abnormality may no longer suffice because multiple defects can be found frequently 6.
Hypercoagulable State Detection
Thromboelastography analysis of whole blood can detect a hypercoagulable state, which may not be detected by plasma PT or aPTT 4.