Optimizing diagnostic testing for venous thromboembolism

What factors can influence the results of thrombophilia testing?

For example, antithrombin is consumed during thrombus formation; therefore, antithrombin levels may be transiently suppressed in acute venous thromboembolism. Moreover, since antithrombin binds to unfractionated heparin, low-molecular-weight heparin, and fondaparinux and mediates their activity as anticoagulants, antithrombin levels may be decreased by heparin therapy.

Similarly, vitamin K antagonists (eg, warfarin) suppress protein C and S activity levels by inhibiting vitamin K epoxide reductase and may falsely indicate a protein C or S deficiency.

Direct oral anticoagulants can cause false-positive results on lupus anticoagulant assays (dilute Russell viper venom time, augmented partial thromboplastin time), raise protein C, protein S, and antithrombin activity levels, and normalize activated protein C resistance assays, leading to missed diagnoses.⁴¹

Since estrogen therapy and pregnancy lead to increases in C4b binding protein, resulting in decreased free protein S, these situations can result in clinicians falsely labeling patients as having congenital protein S deficiency when in fact the patient had a transient reduction in protein S levels.³³

Therefore, to optimize accuracy and interpretation of results, thrombophilia testing should ideally be performed when the patient:

• Is past the acute event and out of the hospital
• Is not pregnant
• Has received the required 3 months of anticoagulation and is off this therapy.

For warfarin, most recommendations say that testing should be performed after the patient has been off therapy for 2 to 6 weeks.⁴² Low-molecular-weight heparins and direct oral anticoagulants should be discontinued for at least 48 to 72 hours, or longer if the patient has kidney impairment, as these medications are renally eliminated.

Genetic tests such as factor V Leiden and prothrombin gene mutation are not affected by these factors and do not require repeat or confirmatory testing.

What if the patient or family wants to understand why an event occurred?

Some experts advocate thrombophilia testing of asymptomatic family members to identify carriers who may need prophylaxis against venous thromboembolism in high-risk situations such as pregnancy, oral contraceptive use, hospitalization, and surgery.²⁹ Asymptomatic family members of a first-degree relative with a history of venous thromboembolism have a 2 times higher risk of an index event.⁴³ Thus, it may be argued that these asymptomatic individuals should receive prophylactic measures in any high-risk situation, based on the family history itself rather than results of thrombophilia testing.

Occasionally, patients and family members want to know the cause of the thrombotic event and want to be tested. In these instances, pretest counseling for the patient and family about the potential implications of testing and shared decision-making between the provider and patient are of utmost importance.²⁹

What is the impact on family members if thrombophilia is diagnosed?

While positive test results can give patients some satisfaction, this knowledge may also cause unnecessary worry, as the patient knows he or she has a hematologic disorder and could possible die of venous thromboembolism.

Thrombophilia testing can have other adverse consequences. For example, while the Genetic Information Nondiscrimination Act of 2008 protects against denial of health insurance benefits based on genetic information, known carriers of thrombophilia may have trouble obtaining life or disability insurance.⁴⁴

Unfortunately, it is not uncommon for thrombophilia testing to be inappropriately performed, interpreted, or followed up. These suboptimal approaches can lead to unnecessary exposure to high-risk therapeutic anticoagulation, excessive durations of therapy, and labeling with an unconfirmed or incorrect diagnosis. Additionally, there are significant costs associated with thrombophilia testing, including the cost of the tests and anticoagulant medications and management of adverse events such as bleeding.

WHAT ARE THE ALTERNATIVES TO THROMBOPHILIA TESTING?

Because discovered thrombophilias (eg, factor V Leiden mutation, prothrombin gene mutation) have not consistently shown a strong correlation with increased recurrence of venous thromboembolism, alternative approaches are emerging to determine the duration of therapy for unprovoked events.

Clinical prediction tools based on patient characteristics and laboratory markers that are more consistently associated with recurrent venous thromboembolism (eg, male sex, persistently elevated D-dimer) have been developed to aid clinicians dealing with this challenging question. Several prediction tools are available:

The “Men Continue and HERDOO2” rule (HERDOO2 = hyperpigmentation, edema, or redness in either leg; D-dimer level ≥ 250 μg/L; obesity with body mass index ≥ 30 kg/m²; or older age, ≥ 65)⁴⁵

The DASH score (D-dimer, age, sex, and hormonal therapy)⁴⁶

The Vienna score,^47,48 at https://cemsiis.meduniwien.ac.at/en/kb/science-research/software/clinical-software/recurrent-vte/.

SUMMARY OF THROMBOPHILIA TESTING RECOMMENDATIONS

Test for thrombophilia only when…

• Discussing with a specialist (eg, hematologist) who has an understanding of thrombophilia
• Using the 4 Ps approach
• A patient requests testing to understand why a thrombotic event occurred, and the patient understands the implications of testing (ie, received counseling) for self and for family
• An expert deems identification of asymptomatic family members important for those who may be carriers of a detected thrombophilia
• The patient with a venous thromboembolic event has completed 3 months of anticoagulation and has been off anticoagulation for the appropriate length of time
• The results will change management.

Forgo thrombophilia testing when…

• A patient has a provoked venous thromboembolic event
• You do not intend to discontinue anticoagulation (ie, anticoagulation is indefinite)
• The patient is in the acute (eg, inpatient) setting
• The patient is on anticoagulants that may render test results uninterpretable
• The patient is pregnant or on oral contraceptives
• Use of alternative patient characteristics and laboratory markers to predict venous thromboembolism recurrence may be an option.

OPTIMIZING THE DIAGNOSIS

With the incidence of venous thromboembolism rapidly increasing, optimizing its diagnosis from both a financial and clinical perspective is becoming increasingly important. Clinicians should be familiar with the use of pretest probability scoring for venous thromboembolism, as well as which diagnostic tests are preferred if further workup is indicated. They should strive to minimize or avoid indiscriminate thrombophilia testing, which may lead to increased healthcare costs and patient exposure to potentially harmful anticoagulation.

Testing for thrombophilia should be based on whether a venous thromboembolic event was provoked or unprovoked. Patients with provoked venous thromboembolism or those receiving indefinite anticoagulation therapy should not be tested for thrombophilia. If testing is being considered in a patient with unprovoked venous thromboembolism, a specialist who is able to implement the 4 Ps approach should be consulted to ensure well-informed, shared decision-making with patients and family members.