What are the results of coagulation studies?

From the Guidelines

Coagulation studies should be interpreted with caution in patients on anticoagulant therapy, as common coagulation assays such as PT and aPTT may not accurately reflect the anticoagulant effect of direct oral anticoagulants (DOACs) 1. When evaluating coagulation studies, it is essential to consider the type of anticoagulant therapy the patient is receiving, as different anticoagulants affect coagulation assays differently. For example, vitamin K antagonists (VKAs) are monitored using PT/INR, while heparin is monitored using aPTT 1.

• DOACs, such as dabigatran, rivaroxaban, apixaban, and edoxaban, affect coagulation assays in a way that is not accurately reflected by PT/INR or aPTT 1.
• Viscoelastic coagulation tests, such as thromboelastography (TEG) and rotational thromboelastometry (ROTEM), may be useful in detecting coagulopathy associated with DOACs, but their interpretation requires expertise and may not be readily available in all hospitals 1.
• A normal aPTT or PT does not rule out the presence of DOACs, and specialized assays such as ecarin clotting time (ECT) or anti-Xa activity may be necessary to accurately measure the anticoagulant effect of DOACs 1.
• The choice of coagulation assay and interpretation of results should be guided by the clinical context and the specific anticoagulant therapy the patient is receiving, with consideration of the potential for bleeding or thrombotic complications 1. In patients on DOACs, viscoelastic coagulation tests such as TEG or ROTEM may be useful in detecting coagulopathy, but their use should be guided by clinical expertise and the availability of specialized assays 1.

From the Research

Coagulation Studies Overview

• Coagulation studies, including prothrombin time (PT) and activated partial thromboplastin time (APTT), are essential for investigating coagulation abnormalities 2.
• These tests can help identify factor deficiencies or inhibitors, which is crucial for directing clinical decisions, such as additional diagnostic testing or factor replacement therapy 3.

Reporting Results of Coagulation Studies

• PT results can be reported as clotting time, percentage activity, PT-ratio, or international normalized ratio (INR) 2.
• APTT results can be reported as clotting time or as a ratio (patient-to-normal clotting time) 2.
• The INR scale is used to harmonize results from different thromboplastins, but its use is limited to patients on treatment with vitamin K antagonists 2.

Causes of Prolonged PT and APTT

• Prolonged PT and APTT can be caused by various factors, including acquired conditions, congenital conditions, or laboratory artifacts 4.
• The most common causes of isolated prolonged PT include vitamin K deficiency, while the most common cause of isolated prolonged APTT is lupus anticoagulant 4.
• Liver disease is a common cause of prolonged PT and APTT 4.

Diagnostic Markers for Coagulopathy

• Biomarkers such as thrombin-antithrombin complex, plasminogen activator inhibitor-1, and protein C activity can be used to identify patients with severe coagulopathy in the initial phase of sepsis 5.
• These biomarkers can help predict the development of overt disseminated intravascular coagulation (DIC) and 28-day mortality 5.

On-Site Coagulation Assays

• On-site coagulation assays can provide rapid results for PT, APTT, and platelet count, which can be useful in clinical settings such as cardiac surgery 6.
• These assays can help identify patients with quantitative deficiencies in platelets and coagulation factors 6.

Mixing Studies

• Mixing studies can be used to investigate unexpected prolonged APTT or PT results and to differentiate between factor deficiencies and inhibitors 3.
• However, there is a lack of standardization for testing protocols and interpretation of mixing study results, which can affect clinical decisions 3.