The Power of Your Choice
Your choice of the IHTC Pharmacy Program directly supports your IHTC team and patient services, and activities provided to the hemophilia community. The IHTC Pharmacy Program provides savings to you and your health insurance plan.
Every patient has the right to choose their clotting factor pharmacy provider. The IHTC supports your right of choice and will assist you in making an informed decision.
Diagnosis of Blood Clots
Diagnosing deep vein thrombosis (DVT) and pulmonary embolism (PE) may be difficult as the signs and symptoms associated with these disorders are not unique to these conditions. For example, leg pain and swelling or chest pain and shortness of breath may be related to various other causes. As a result, objective testing is needed to confirm the diagnosis. Venography and pulmonary angiography remain the gold standards for diagnosis of DVT and PE, respectively, but these tests are now increasingly being replaced by less invasive and less expensive procedures. Such noninvasive tests are often incorporated into diagnostic worksheets that are designed to limit the need for more invasive procedures.1
Three types of imaging tests may be used to diagnose clots in veins:
Tests using radio labels
Radioactive fibrinogen leg scanning: This test is moderately sensitive and specific for clots in the calf and popliteal veins, but less sensitive for superficial clots in the femoral or ileac veins. (see http://www.health.com/health/library/mdp/0,,zm2346,00.html for graphic of different veins)
The AcuTect Venogram: The AcuTect is a synthetic radiochemical that binds to a protein (GP IIa/IIIb receptor) found on activated platelets. The AcuTect venogram is used to diagnose acute venous clots in the lower extremities of patients with signs and symptoms of such clots. The AcuTect appears to detect acute but not chronic clots in the veins.
Tests using ultrasound
Doppler-augmented ultrasound and impedance plethysmography (IPG): This technique is sensitive to proximal clots that cause blockages. IPG does not detect calf vein clots and proximal vein clots that do not block the blood vessel.
Doppler ultrasonography: This is the most widely used and available noninvasive test for DVT. Doppler ultrasonography has become the dominant test since the 1980′s and has largely replaced IPG for noninvasive testing.
Tests using X-rays or computed tomography
Venography: This method of testing can detect clots in both calf and proximal veins.
V/Q scans: V/Q scanning may be used as a one-step method to diagnose pulmonary embolism (PE) in patients with a normal chest radiograph. In patients with an abnormal chest radiograph, V/Q scanning should be used in combination with spiral CT. V/Q scans tend to be used mainly to exclude rather than confirm PE.3 V/Q scanning is able to show even small clots and this ability is enhanced by single photon emission computed tomography (SPECT).
Helical spiral computed tomography (spiral CT): This technique is very effective in diagnosing clinically important PE and a large number of alternative diagnoses in patients with symptoms who have undergone a V/Q scan. This is an accurate method for detecting and excluding most types of PE.
The use of D-dimer assays to rule out the diagnosis of a clotting condition is controversial. The accuracy of the D-dimer test depends on the patient setting. The D-dimer test is accurate in outpatients, but in hospitalized patients, the accuracy of the elevated D-dimer result may reflect clots or medical conditions other than PE that lead to an increase in D-dimer concentration.4
D-dimer levels may be able to predictive the chance of recurrence of a clot after stopping oral blood thinners. Normal levels obtained 1 month after stopping therapy indicate that recurrence is less likely, especially in people with previous unprovoked blood clots, regardless of whether they are carriers of a form of an inherited clotting disorder.5
Special Considerations for Diagnosis of Antiphospholipid Syndrome (APS)
Patients with APS should have at least one clinical and one persistent laboratory finding documented to confirm that they have APS. The antiphospholipid antibody test (APA) should be positive on at least two occasions greater than 8 weeks apart. Often APS may be diagnosed in people with an autoimmune disorder such as systemic lupus erythematosus (SLE). APS can also occur in people without a systemic disease. This latter group of patients is referred to as having primary antiphospholipid-protein syndrome (PAPS). In some patients, PAPS may progress to SLE over time. APS may also be induced by drugs or cancer.
Special Considerations for Diagnosis of Heparin-Induced Thrombocytopenia (HIT)
The diagnosis of suspected HIT should be based on a clinical assessment made by a medical care provider experienced with this condition, along with various specialized laboratory tests. Laboratory assays for diagnosing HIT are described here. If HIT is confirmed, all forms of heparin must be stopped. This includes the removal of heparin-coated catheters and the discontinuation of all heparin flushes of catheters.
- Weitz JI. Diagnosis of Deep Venous Thrombosis and Pulmonary Embolism. Presentation at the Surgeon General Workshop on Deep Vein Thrombosis. 2006. Available at: http://www.surgeongeneral.gov/topics/deepvein/workshop/agenda.html . Accessed March 10, 2010.
- Niethammer JG 3rd, et al. Pulmonary embolism. How V/Q scanning helps in diagnosis. Postgrad Med. 1990 Jan;87(1):263-7, 270.
- Schümichen C. V/Q-scanning/SPECT for the diagnosis of pulmonary embolism. Respiration. 2003;70:329-342.
- Schrecengost J, et al. Comparison of diagnostic accuracies in outpatients and hospitalized patients of D-dimer testing for the evaluation of suspected pulmonary embolism. Clin Chem. 2003;49:1483-1490.
- Palareti G, et al. Predictive value of D-dimer test for recurrent venous thromboembolism after anticoagulation withdrawal in subjects with a previous idiopathic event and in carriers of congenital thrombophilia. Circulation. 2003;108:313-318.