PTT or aPTT

1.What is PTT blood test?

The partial thromboplastin time (PTT), or activated partial thromboplastin time (aPTT), serves as a preliminary assessment to determine an individual's competence in forming blood clots effectively. This test gauges the time, measured in seconds, required for a blood clot to develop within a blood sample following the introduction of specific substances (reagents). PTT evaluates the quantity and functionality of specific blood proteins known as coagulation or clotting factors, which play a vital role in the blood clot formation process.

2.What does PTT test show?

PTT is primarily employed to explore instances of unexplained bleeding or clotting. It is often prescribed alongside a prothrombin time (PT/INR) test to scrutinize the body's clot formation process, which aids in arresting bleeding. These tests typically serve as the initial steps in the examination of disorders associated with excessive bleeding or clotting.

By assessing the outcomes of both tests in conjunction, a healthcare provider can glean insights into the potential bleeding or clotting disorder at hand. While the PTT and PT are not diagnostic in themselves, they commonly offer insights into whether additional tests may be warranted.

3.When should this test be requested?

A PTT test may be requested in the following scenarios:

1. As part of an assessment for lupus anticoagulant, anticardiolipin antibodies, and antiphospholipid syndrome, particularly when there is a history of blood clots or recurrent miscarriages in women.
2. During the transition from heparin therapy to longer-term warfarin (Coumadin) therapy, both PTT and PT tests are monitored until stabilization is achieved.
3. Prior to a scheduled surgical procedure, especially when the surgery carries an elevated risk of blood loss, or when there is a medical history of bleeding issues, such as frequent or excessive nosebleeds and easy bruising, suggesting a potential bleeding disorder.

4.What tests can be ordered along with PTT test?

The PTT test may be requested alongside other tests, including a PT, when you exhibit:

1. Unexplained bleeding tendencies or a propensity for easy bruising.
2. A documented blood clot within a vein or artery.
3. An acute medical condition, such as disseminated intravascular coagulation (DIC), characterized by a simultaneous occurrence of bleeding and clotting due to rapid depletion of coagulation factors.
4. A chronic health condition like liver disease, which may influence blood clotting mechanisms.

5.How can the test results be interpreted?

PTT results are typically reported in seconds.

A PTT result that falls within a laboratorys reference range usually indicates normal clotting function. However, it's important to note that even with a normal PTT result, mild to moderate deficiencies of a single coagulation factor may be present. Prolongation of the PTT may not become evident until the factor levels have decreased to 30% to 40% of normal. Conversely, the presence of lupus anticoagulant (LA) may not significantly extend the PTT result. If there is suspicion of lupus anticoagulant (LA), a more sensitive LA-sensitive PTT or a dilute Russell viper venom time (DRVVT) can be employed for testing. (See below for additional information on LA-sensitive PTT.)

A prolonged PTT implies that the process of blood clotting is taking longer than usual to occur and may be attributed to various underlying causes.

A prolonged PTT indicates that the blood is taking longer than normal to clot and may have various underlying causes, including:

1. Underlying conditions that lead to low levels of clotting factors, such as:

- Liver disease: Most coagulation factors are produced by the liver, so liver disease can cause prolonged PT and PTT. However, PT is more likely to be prolonged than PTT.

- Vitamin K deficiency: Vitamin K is essential for the formation of several clotting factors. Vitamin K deficiencies can result from a poor diet, malabsorption disorders, or prolonged use of specific antibiotics, for instance. PT is more likely to be prolonged than PTT.

1. Less common inherited clotting factor deficiencies:

- von Willebrand disease (vWD): This is the most common inherited bleeding disorder and affects platelet function due to decreased von Willebrand factor. In most cases of vWD, PTT is normal but can be prolonged in severe cases.

- Hemophilia A and hemophilia B (Christmas disease): These are other inherited bleeding disorders that result from a decrease in factors VIII and IX, respectively.

- Deficiencies of other coagulation factors, such as factors XII and XI: Deficiency in factor XI can cause abnormal bleeding, but factor XII deficiency is not associated with bleeding risk in the body.

1. Nonspecific inhibitors, such as lupus anticoagulant: This is an autoantibody (antiphospholipid antibody) that interferes with PTT by targeting substances called phospholipids used in the test. While they can prolong the PTT result, they are associated with excessive clotting in the body. Individuals producing these antibodies may be at an increased risk of blood clots.
2. Specific inhibitors: These relatively rare antibodies specifically target certain coagulation factors (known as factor-specific inhibitors), affecting their function. An example is an antibody targeting factor VIII, which can cause severe bleeding.
3. Anticoagulants:

- Heparin: Heparin is an anticoagulant and can prolong PTT, either as a contaminant of the sample or as part of anticoagulation therapy. For anticoagulant therapy, the target PTT is often about 1.5 to 2.5 times longer than a person's pretreatment level. PTT is still used to monitor standard heparin therapy.

- Warfarin (Coumadin) anticoagulation therapy: PTT is not used to monitor warfarin therapy, but high doses of warfarin can prolong PTT. Typically, the prothrombin time/international normalized ratio (PT/INR) is used to monitor warfarin therapy.

- Other anticoagulants: Anticoagulation therapy with direct thrombin inhibitors (e.g., argatroban, dabigatran) or direct factor Xa inhibitors (e.g., rivaroxaban, apixaban).

- Prolonged PTT levels may also be observed in certain types of leukemia, excessive bleeding in pregnant women before or after childbirth, or recurrent miscarriages.

The interpretation of PTT results is often done in conjunction with PT results to determine the underlying condition that may be present.

6.What is an LA-sensitive PTT, and how does it distinguish itself from the standard PTT?

The LA-sensitive PTT (LA-PTT or PTT-LA) is a specialized version of the partial thromboplastin time (PTT) test, specifically designed to detect the presence of lupus anticoagulant (LA). Lupus anticoagulant is an antibody associated with abnormal blood clotting and recurrent miscarriages. The LA-PTT employs a low phospholipid reagent that is finely tuned to detect lupus anticoagulants, making it more sensitive in identifying their presence. This test operates on the principle that lupus anticoagulants interact with the phospholipids used in the PTT test, leading to an abnormally prolonged clotting time.

7.what other tests might be done besides PTT test?

Additional tests that may be conducted alongside a PTT or as a follow-up to abnormal PTT results include:

1. Platelet count: This should be regularly monitored during heparin therapy to promptly identify any heparin-induced thrombocytopenia.
2. Thrombin time testing: Sometimes ordered to help exclude heparin contamination as a factor affecting clotting.
3. Fibrinogen testing: May be performed to rule out a low fibrinogen level as a potential cause of an extended PTT.

In cases where an initial PTT result is prolonged, a second PTT test is typically conducted by mixing the individual's plasma with pooled normal plasma, which comprises plasma from several healthy donors. If the PTT time returns to normal ("corrects"), it suggests a deficiency of one or more coagulation factors in the individual's plasma. If the time remains prolonged, the issue may be attributed to the presence of an abnormal factor-specific inhibitor (autoantibody) or a nonspecific inhibitor, such as lupus anticoagulant.

Other related tests may include:

1. Coagulation factor tests: These assess the activity (function) of coagulation factors, identifying reduced levels or factors that exhibit diminished function. In some cases, the antigen level (quantity) of a coagulation factor may also be measured.
2. Dilute Russell viper venom test (DRVVT): This test may be performed if lupus anticoagulant is suspected.
3. von Willebrand factor: Occasionally ordered to help determine if severe von Willebrand disease is responsible for a prolonged PTT.

8.What activities can change my PTT?

The PTT is not influenced by lifestyle changes (unless a vitamin K deficiency is the underlying cause). It serves as an indicator of your clotting system's function and integrity. If your PTT is prolonged due to acquired factor deficiencies, addressing the root cause of the deficiency can help normalize the results. In cases where the prolongation is linked to a temporary or acute condition, the PTT should naturally return to normal as the acute condition resolves. Inherited coagulation abnormalities or deficiencies require close monitoring and may involve frequent replacement infusions of the deficient clotting factor as part of treatment.