Activated Protein C-Resistance

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Also known as: Activated protein C resistance, Activated Protein CResistance, APC resistance, Factor II 20210, Factor V Leiden mutation, Factor V R506Q, Prothrombin 20210 mutation, PT G20210A

Activated Protein C

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The Activated Protein C-Resistance test contains 1 test with 1 biomarker.

Brief Description: The Activated Protein C-Resistance (APC-R) test is a laboratory assay primarily used to assess the risk of venous thrombosis. It determines how well the anticoagulant pathway of the blood, involving protein C, is working. A malfunction in this pathway can lead to an increased risk of blood clot formation.

Collection Method: Blood Draw

Specimen Type: Serum

Test Preparation: No preparation required

When and Why an Activated Protein C-Resistance Test May Be Ordered

This test is typically ordered when a person has experienced an unexplained venous thromboembolism, especially at a young age, or when there's a family history of recurrent clotting events. It can also be useful in the following scenarios:

  1. To determine the cause of recurrent miscarriages.
  2. When a woman experiences a clotting event during pregnancy or while taking oral contraceptives.
  3. For patients with a personal or family history of venous thrombosis without apparent risk factors.

What an Activated Protein C-Resistance Test Checks For

The APC-R test essentially measures the ability of activated protein C to inhibit blood clotting. When protein C is activated in the body, it should prolong the clotting time. If the clotting time doesn't extend as expected in the presence of activated protein C, resistance to APC is suggested.

A common genetic mutation associated with APC resistance is the Factor V Leiden mutation. However, the APC-R test does not directly test for this mutation but indicates its possible presence.

Other Lab Tests Ordered Alongside an Activated Protein C-Resistance Test

When an APCR test is ordered, it's typically part of a broader evaluation for thrombophilia (an increased tendency to form abnormal blood clots). Here are some tests commonly ordered alongside it:

  1. Factor V Leiden Mutation Test:

    • Purpose: To check for the presence of the Factor V Leiden mutation, the most common genetic cause of APCR.
    • Why Is It Ordered: To confirm if the protein C resistance is due to this specific genetic mutation.

  2. Prothrombin G20210A Mutation Test:

    • Purpose: To detect the presence of a mutation in the prothrombin gene, another common genetic risk factor for thrombophilia.
    • Why Is It Ordered: To identify additional genetic factors that may contribute to an increased risk of blood clots.

  3. Complete Blood Count (CBC) with Differential:

    • Purpose: To evaluate overall blood health.
    • Why Is It Ordered: To identify any underlying conditions that might contribute to clotting disorders, such as polycythemia (increased red blood cell count).

  4. Antithrombin Activity:

    • Purpose: To measure the activity of antithrombin, a protein that helps regulate blood clotting.
    • Why Is It Ordered: Deficiencies in antithrombin can lead to an increased risk of thrombosis.

  5. Protein C and Protein S Activity:

    • Purpose: To measure the activity of proteins C and S, which are important in controlling blood clotting.
    • Why Is It Ordered: Deficiencies or abnormalities in these proteins can increase the risk of developing blood clots.

  6. Lupus Anticoagulant and Anticardiolipin Antibodies:

    • Purpose: To check for the presence of these antibodies, which are associated with an increased risk of clotting and are markers for antiphospholipid syndrome.
    • Why Is It Ordered: To assess for other causes of thrombophilia, especially in individuals with a history of recurrent clots or miscarriages.

  7. D-Dimer Test:

    • Purpose: To measure a substance that is released when a blood clot breaks up.
    • Why Is It Ordered: Elevated levels can indicate recent clot formation and breakdown, although this test is not specific for diagnosing thrombophilia.

  8. Coagulation Panel (PT/INR, aPTT):

    • Purpose: To assess the blood’s ability to clot.
    • Why Is It Ordered: To provide a general overview of the clotting system, although these tests are often normal in individuals with thrombophilia.

These tests, when ordered alongside an Activated Protein C-Resistance test, provide a comprehensive evaluation of a person's risk for thrombophilia. They are crucial for identifying the cause of clotting disorders, assessing the risk of future clotting events, and guiding treatment and management decisions. The specific combination of tests will depend on the individual’s clinical history, family history, and any previous episodes of abnormal clotting.

Conditions or Diseases Requiring an Activated Protein C-Resistance Test

The primary conditions associated with APC resistance include:

  1. Deep Vein Thrombosis (DVT): A clot in a deep vein, usually in the legs.
  2. Pulmonary Embolism (PE): A clot that travels to the lungs, which can be life-threatening.
  3. Recurrent Miscarriage: Especially when no other causes can be identified.
  4. Unexplained Thrombosis: Clotting events without typical risk factors such as surgery, trauma, or extended immobilization.

How Health Care Providers Use the Results of an Activated Protein C-Resistance Test

The results of the APC-R test help healthcare providers identify individuals at an increased risk of clotting events. If resistance is detected, it's crucial to determine its cause, especially if it's genetic. This information can influence treatment decisions and preventive measures.

Patients found to have APC resistance may be counseled about the risks and benefits of anticoagulant therapy, especially in situations where clotting risk is elevated, like surgery or pregnancy. Furthermore, knowing about APC resistance can influence decisions about medications, such as hormone replacement therapy or oral contraceptives, which can increase clotting risk.

Most Common Questions About the Activated Protein C-Resistance test:

Purpose and Clinical Indications

Why is the Activated Protein C-Resistance test performed?

The Activated Protein C-Resistance test is primarily conducted to determine the risk of inappropriate blood clot formation. This test is often used to detect Factor V Leiden mutation, a common inherited genetic disorder that can cause abnormal clotting of the blood, increasing the risk for deep vein thrombosis (DVT) and pulmonary embolism.

What differentiates the Activated Protein C-Resistance test from other coagulation tests?

The Activated Protein C-Resistance test specifically evaluates how plasma (a component of blood) responds to activated protein C, an anticoagulant. If plasma is resistant to the anticoagulant effects of activated protein C, it suggests the presence of Factor V Leiden mutation. Other coagulation tests may focus on different clotting factors or pathways in the coagulation cascade.

Interpretation of Results

What does a positive Activated Protein C-Resistance test indicate?

A positive Activated Protein C-Resistance test means that an individual's plasma shows resistance to the anticoagulant effects of activated protein C. This is often indicative of the presence of the Factor V Leiden mutation. However, further genetic testing would be needed to confirm this mutation.

How does the result of the Activated Protein C-Resistance test influence treatment decisions?

If the Activated Protein C-Resistance test is positive, it suggests an increased risk of abnormal blood clotting. Physicians might consider recommending prophylactic anticoagulation therapy, especially during high-risk situations like surgery or prolonged immobility. Additionally, lifestyle modifications, regular monitoring, and genetic counseling may be suggested, especially if the patient has a family history of clotting disorders.

Clinical Implications

Is the Activated Protein C-Resistance test recommended for individuals with a family history of thrombosis?

Yes, the Activated Protein C-Resistance test is particularly beneficial for those with a family history of thrombosis, especially if a family member has been diagnosed with Factor V Leiden mutation. Identifying individuals who have this mutation can help in managing and potentially preventing thrombotic episodes.

Can the Activated Protein C-Resistance test be used in conjunction with other coagulation tests?

Yes, the Activated Protein C-Resistance test is often performed alongside other coagulation tests to get a comprehensive understanding of an individual's clotting profile. Tests like prothrombin time (PT), partial thromboplastin time (PTT), and specific factor assays can provide additional information about the overall functioning of the clotting system.

We advise having your results reviewed by a licensed medical healthcare professional for proper interpretation of your results.

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