The Partial Thromboplastin Time, Activated (aPTT) test contains 1 test with 1 biomarker.
Description: A PTT test is used to diagnose and monitor bleeding disorders or excessive clotting disorders. The biomarker in the test is used to measure the tsime it takes for the blood to form a clot.
Also Known As: Activated Partial Thromboplastin Time Test, aPTT test, PTT Test
Collection Method: Blood Draw
Specimen Type: Whole Blood
Test Preparation: No preparation required
Average Processing Time: 1 to 2 days
When is Partial Thromboplastin Time test ordered?
When a person has the following symptoms, the PTT may be ordered along with other tests, such as a PT:
- Bleeding that isn't explained or bruises that isn't easy to get rid of
- A blood clot in a vein or artery is a serious condition.
- Disseminated intravascular coagulation
- A chronic disorder that affects hemostasis, such as liver disease
A PTT can be requested in the following situations:
- When a person develops a blood clot or a woman has repeated miscarriages, as part of a lupus anticoagulant, anticardiolipin antibodies, or antiphospholipid syndrome examination
- When a person is on standard heparin therapy, the two are overlapped and both the PTT and PT are monitored until the person has stabilized. When a person is switched from heparin therapy to extended warfarin therapy, the two are combined and both the PTT and PT are monitored until the person has stabilized
- Prior to surgery, if there is a high risk of blood loss and/or if the patient has a history of bleeding, such as frequent or severe nasal bleeds and easy bruising, which could suggest the presence of a bleeding problem
What does a Partial Thromboplastin Time blood test check for?
The partial thromboplastin time is a screening test that determines a person's capacity to form blood clots properly. It counts how long it takes for a clot to develop in a person's blood sample after chemicals have been administered. The PTT evaluates the number and function of specific proteins known as coagulation factors, which are crucial in blood clot formation.
When bodily tissues or blood vessel walls are harmed, bleeding ensues, and hemostasis is initiated. Platelets are little cell fragments that cling to the damage site and subsequently clump together. A process known as the coagulation cascade begins at the same time, and coagulation factors are activated. Fibrin threads develop and crosslink into a net that attaches to the damage site and stabilizes it as a result of the cascade reactions. This, combined with the platelets sticking, forms a stable blood clot that seals off injuries to blood arteries, prevents further blood loss, and allows damaged areas to heal.
For appropriate blood clot formation, each component of this hemostatic mechanism must operate effectively and be present in sufficient quantities. If one or more of these factors are deficient, or if they function improperly, a stable clot may not form, and bleeding may continue.
A PTT compares a person's sample to a normal clotting time reference period. A person's PTT is considered "prolonged" if it takes longer than usual to clot. A prolonged PTT could be caused by a disease that causes one or more coagulation factors to diminish or become dysfunctional. It's also possible that it's caused by a disorder in which the body creates antibodies that attack one or more coagulation factors, impairing their activity.
A PTT may take longer than expected if the person being tested creates an autoantibody termed an antiphospholipid antibody, which interferes with the test. Because it targets phospholipids, which are employed in the PTT, this type of antibody has an effect on the test findings. Antiphospholipid antibodies can extend the PTT test result, although they are linked to increased clotting in the body. A person who makes these antibodies may be more susceptible to blood clots. A PTT could be used to assess someone who has signs and symptoms of excessive clotting or antiphospholipid syndrome.
A PTT is frequently ordered in conjunction with a prothrombin time while investigating bleeding or clotting episodes. The results of these tests will be analyzed by a health professional in order to discover the reason of bleeding or clotting episodes.
Coagulation tests like the PT and PTT are now known to be reliant on what happens artificially in the test setting and so do not always reflect what happens in the body. They can, however, be utilized to assess certain aspects of the hemostasis system. The PTT and PT tests measure coagulation components that are part of the intrinsic, extrinsic, and common chemical reaction pathways in the cascade, respectively.
Lab tests often ordered with a Partial Thromboplastin Time test:
- PT and INR
- Fibrinogen
- D-Dimer
- Lupus Anticoagulant
- ACT
- Coagulation Factors
- Platelet Count
- Complete Blood Count (CBC)
- Von Willebrand Factor
- Antiphospholipid Antibodies
Conditions where a Partial Thromboplastin Time test is recommended:
- Bleeding Disorders
- Excessive Clotting Disorders
- Vitamin K Deficiency
- DIC
- Antiphospholipid Syndrome
How does my health care provider use a Partial Thromboplastin Time test?
The PTT is mostly used to look into unexplained bleeding or clotting. It may be ordered in conjunction with a prothrombin time test to assess hemostasis, the body's process of forming blood clots to stop bleeding. Excessive bleeding or clotting issues are frequently investigated with these tests as a starting point.
Coagulation factors are proteins that have a role in hemostasis and the development of blood clots. When an injury occurs and bleeding begins, coagulation factors are triggered in a series of events that finally assist in the formation of a clot.
Prekallikrein and high molecular weight kininogen, as well as coagulation factors XII, XI, IX, VIII, X, V, II, and I, are all assessed using the PTT. The coagulation factors VII, X, V, II, and I are evaluated in a PT test. A health practitioner can determine what type of bleeding or clotting condition is present by combining the findings of the two tests. The PTT and PT aren't diagnostic, but they can help you figure out if you need more tests.
The following are some examples of PTT applications:
- To detect coagulation factor deficit; if the PTT is extended, additional tests can be performed to ascertain whether coagulation factors are deficient or malfunctioning, or to see if the blood contains an antibody to a coagulation factor.
- Nonspecific autoantibodies, such as lupus anticoagulant, can be detected and are linked to clotting episodes and recurrent miscarriages. As a result, PTT testing may be included in a clotting disorder panel to aid in the investigation of recurrent miscarriages or the diagnosis of antiphospholipid syndrome. The LA-sensitive PTT, a version of the PTT, could be used for this.
- Heparin is an anticoagulant medicine that is given intravenously or by injection to prevent and treat blood clots; it is used to monitor routine heparin anticoagulant therapy. PTT is extended as a result of it. Heparin must be constantly managed when it is used for medicinal purposes. If too much is given, the patient may bleed excessively; if not enough is given, the patient may continue to clot.
The PTT and PT tests are sometimes used to screen for potential bleeding tendencies before surgical or other invasive treatments based on carefully acquired patient histories.
Other tests that may be done in conjunction with a PTT or in response to aberrant results include:
- Platelet count — should be checked often during heparin therapy to detect any thrombocytopenia caused by the drug.
- Thrombin time testing – used to rule out the possibility of heparin contamination.
- Fibrinogen testing - to rule out a low level of fibrinogen as the cause of a delayed PTT.
- A second PTT test is conducted after a first PTT is delayed by mixing the person's plasma with pooled normal plasma. If the PTT time returns to normal, it indicates that one or more coagulation factors in the person's plasma are deficient. If the condition persists, it could be caused by the presence of an aberrant specific factor inhibitor or nonspecific lupus anticoagulant.
- Coagulation factor tests are used to determine how active coagulation factors are. They can identify low protein levels or proteins that aren't working properly. A coagulation factor's antigen level is occasionally tested.
- If the presence of lupus anticoagulant is suspected, a test for dilute Russell viper venom may be performed.
- Von Willebrand factor is a test that is sometimes conducted to see if von Willebrand disease is causing a prolonged PTT.
What do my Partial Thromboplastin Time test results mean?
PTT findings are usually available in seconds. A normal clotting function is usually indicated by a PTT result that falls within a laboratory's reference interval. However, a single coagulation factor deficiency may be present in low to moderate amounts. The PTT should not be extended until the factor levels have dropped to 30% to 40% of normal. Lupus anticoagulant may also be present, but it is unlikely to affect the PTT result. A more sensitive LA-sensitive PTT or a dilute Russell viper venom time can be used to test for the lupus anticoagulant if it is suspected.
A delayed PTT indicates that clotting is taking longer than usual and could be caused by a number of factors. This frequently indicates that the body's clotting ability is being harmed by a coagulation factor deficit or a particular or nonspecific antibody. Defects in coagulation factors can be acquired or inherited.
It's possible that prolonged PTT tests are caused by:
- Von Willebrand disease is the most prevalent inherited bleeding disorder, and it inhibits platelet function because von Willebrand factor levels are low.
- Hemophilia A and B are two more inherited bleeding disorders that are caused by a lack of factors VIII and IX, respectively.
- Other coagulation factors, such as factors XII and XI, are deficient.
Deficiencies in acquired factors:
- A vitamin K insufficiency. Vitamin K is required for the production of clotting factors. Vitamin K deficiency is uncommon, but it can occur as a result of a poor diet, malabsorption issues, or the use of certain antibiotics over an extended period of time, for example.
- Because the liver produces the majority of coagulation components, liver illness might result in extended PT and PTT. PT is more likely to be prolonged than PTT in patients with liver disease and vitamin K insufficiency.
- A nonspecific inhibitor, such as lupus anticoagulant—the presence of these inhibitors is usually linked to abnormal clotting, but they can also lengthen the PTT. For further information, see the individual test articles.
- Antibodies that selectively target certain coagulation factors, such as antibodies that target factor VIII, are known as specific inhibitors. They can form in people who are receiving factor replacements or they can develop spontaneously as an autoantibody in people who have a bleeding condition. Factor-specific inhibitors have the potential to induce serious bleeding.
- Heparin is an anticoagulant that will prolong a PTT if it is present in the sample as a contaminant or as part of anticoagulation therapy. The goal PTT for anticoagulant therapy is usually 1.5 to 2.5 times longer than the pretreatment level.
- The PTT is not used to monitor warfarin anticoagulation therapy, but it may be influenced by it. The PT is commonly used to track warfarin therapy.
- Anticoagulation therapy with a direct thrombin inhibitor or a direct factor Xa inhibitor are examples of other anticoagulants.
- Leukemia, severe bleeding in pregnant women prior to or after delivery, and recurrent miscarriages can all cause elevated PTT levels
The PTT results are frequently combined with the PT results to determine what ailment is present.
PTT testing may be shortened as a result of:
- Disseminated intravascular coagulation—circulating procoagulants shorten the PTT in the early phases of DIC.
- Extensive cancer
- An acute-phase reaction is a disease that causes significant tissue inflammation or trauma, which causes factor VIII levels to rise. It's frequently a one-time occurrence that isn't tracked with a PTT test. The PTT will return to normal once the condition that caused the acute phase reaction is resolved.
We advise having your results reviewed by a licensed medical healthcare professional for proper interpretation of your results.
