Partial Thromboplastin Time (PTT, aPTT)

If you’re experiencing symptoms, such as excessive or unexplained bleeding, your doctor may order a PTT test to determine if any of the proteins or factors involved in blood clotting are missing or not functioning properly. An activated partial thromboplastin time (aPTT) test is the same test as a PTT but takes less time and is considered more sensitive.

This guide provides an overview of how a PTT or aPTT test works, why a doctor may order the test, some of the bleeding disorders and conditions that may lead to abnormal PTT test results, and treatment options.

The purpose of a PTT test is to determine whether your blood is clotting normally. If you’re taking a blood-thinning drug, such as heparin, your doctor may also order a PTT test to help determine appropriate dosage levels.

You may need a PTT test if you:

• Are experiencing heavy bleeding
• Bruise easily
• Have recurrent miscarriages
• Have liver disease
• Have a family history of bleeding disorders
• Take an anticoagulant, such as heparin or warfarin

A PTT test requires you to visit a health clinic to have a sample of your blood drawn and tested at a laboratory.

No preparation is required for a PTT, but it’s important to advise your clinician of all medications you’re taking prior to the test. Drugs, such as aspirin or heparin, may affect your results.

It’s important that your body is able to clot blood to prevent excessive bleeding when you’re injured.

Blood clotting is a complex process that involves more than a dozen types of proteins produced by the liver. Known as clotting factors or coagulation factors, these proteins work together after the body experiences a trauma or injury. They interact with tiny blood cells called platelets to form a clot that stops bleeding in a sequence known as the coagulation cascade. As the blood vessel heals, the clotting process stops, and the clot dissolves.

A missing or defective clotting factor affects the coagulation cascade, causing the body to take longer to form a clot. This results in a bleeding disorder that may range from mild to severe, depending on how deficient the factors are.

Symptoms of a blood clotting disorder may include:

• Bruises that frequently occur with little or no trauma, from one to four times per month
• Extensive bleeding from cuts, minor surgical procedures, immunizations, blood draws, and dental work that doesn’t stop with pressure
• Frequent nosebleeds (more than five times per year), lasting more than ten minutes
• Heavy menstrual bleeding that involves the passing of clots larger than the size of a quarter
• Swelling, stiffness, or pain that results from bleeding into muscles, joints, and soft tissues
• Purple or red spots caused by bleeding under the skin, known as petechiae

There are a number of conditions that may cause your body to have difficulty clotting blood. They may be passed down genetically in a family or acquired later in life.

• Von Willebrand Disease (VWD) is the most common bleeding disorder, affecting about 1% of Americans. It occurs in both men and women who have a missing or defective Von Willebrand clotting factor protein. About 60% to 80% of patients experience the mildest form, Type 1 VWD. Type 2 VWD occurs in up to 30% of patients and may be mild to moderate. Up to 10% of patients have Type 3 VWD and experience severe bleeding symptoms. While this disorder is typically genetic, some adults acquire VWD as the result of an autoimmune disease.
• Hemophilia affects about 20,000 males in the United States or 1 of every 5,000 male births. Hemophilia is inherited and caused by low levels of factor VIII (Hemophilia A) or factor IX (Hemophilia B). The lower the levels, the more difficulty the body has clotting blood, and the more severe the condition. Hemophilia may result in excessive bleeding after injury and spontaneous bleeding. In rare cases, the condition can be acquired later in life by middle-aged or elderly people, as well as young women who are pregnant or have just given birth.
• Disseminated intravascular coagulation (DIC) is a rare but life-threatening condition that is caused by cancer, inflammation, or infection. In this condition, clotting proteins are overactive, leading to their depletion. It may also involve the formation of small blood clots that can prevent blood from flowing to organs.
• Bleeding from vitamin K deficiency is most likely to occur in infants and newborns who do not have enough vitamin K to form blood clots. It causes bleeding inside or outside of the body and affects anywhere from 1 in 60 to 1 in 250 babies. Babies typically receive a vitamin K shot at birth as protection. Adults are unlikely to develop this deficiency because vitamin K is produced by the body and is also found in foods, such as green vegetables. Bleeding from a vitamin K deficiency is usually treatable.

Other conditions that may lead to blood clotting disorders include:

• Anemia
• Liver cirrhosis
• HIV
• Leukemia
• Coagulation factor deficiencies (named for the factor that is missing, such as Factor I or Factor II)
• The use of blood-thinning medications, such as aspirin, heparin, and warfarin

A partial thromboplastin time (PTT) test is also known as an activated partial thromboplastin time (aPTT) test or an intrinsic pathway coagulation factor profile.

To perform the test, a sample of blood is drawn from your arm. A healthcare practitioner:

• Examines your arm to locate a vein from which to draw blood, typically on the inside of your forearm, near the elbow
• Applies a tourniquet around the upper arm to make it easier to draw a blood sample from the vein
• Cleans and disinfects the puncture site with an alcohol swab
• Inserts a small needle to draw a sample of blood into a small tube
• Removes the tourniquet and needle and applies pressure to the puncture site

The sample is collected in a tube that contains citrate ions, which prevent the blood from clotting before the test begins. The sample is then sent to a lab for analysis.

The PTT test is performed by a technician who starts the blood clotting process in the lab by extracting plasma from the blood sample and adding calcium and other substances. An aPTT is the same test as a PTT, but with other activators to speed up clotting time and provide a narrower range of reference.

The technician then measures how long it takes your blood to clot in seconds. This tests how the specific coagulation factors in your body are functioning. If any are deficient, it takes longer than normal for your blood to clot and you have an elevated PTT.

PTT and aPTT tests are typically ordered by your physician when there are concerns regarding your symptoms. In some cases, you may be able to order the test directly on some websites. You can download the test requisition and take it to a diagnostic laboratory near you. The results are provided to you electronically.

Most bleeding disorders are lifelong conditions. While there is no cure, they are manageable.

Treatment depends on the condition and its severity. It may involve episodic care to stop bleeding when it happens or prophylactic care to prevent bleeding from occurring. Your doctor can recommend an appropriate treatment plan, which may include the following:

• Clotting factor replacement therapy, which involves an infusion of the deficient blood clotting factor so that blood can clot properly
• Medication, such as desmopressin acetate, which comes in a nasal spray or injection and helps the cells to release VWF proteins

Depending on your condition, you may be referred to a hematologist who specializes in the treatment of blood disorders. There are also federally-funded hemophilia treatment centers across the country that provide comprehensive care and education to patients with bleeding disorders. These centers have multidisciplinary teams consisting of hematologists, blood specialists, nurses, physical therapists, social workers, mental health professionals, and other healthcare providers to help patients better understand and manage their condition.

To determine your test results, your PTT is compared to a normal control value. This value varies by laboratory, but generally, a normal range is 60 to 70 seconds for a PTT and 30 to 40 seconds for an aPTT. Keep in mind that your health and other factors must also be considered. Review your test results with your physician.

An elevated PTT is higher than a normal PTT, which means that your blood takes longer to clot than normal. Possible reasons include a blood disorder, liver disease, an autoimmune disease, or vitamin K deficiency.

If your PTT is higher than normal, your doctor can order other tests, such as factor assays, to determine which clotting factors are deficient and to help diagnose underlying health conditions.

No. It only detects if your blood is not clotting properly.

No. A PTT only evaluates certain clotting factors, including I, II, V, VIII, IX, X, XI, and XII. It is commonly, but not always, done with tests, such as a Prothrombin Time (PT) or fibrinogen activity test, to provide additional information regarding deficiencies of clotting factors.

You may experience minor bruising at the site where blood is drawn, but there is very little risk associated with a PTT test.

To learn more about blood clotting disorders and testing for these conditions, use the following resources.

1. https://medlineplus.gov/lab-tests/partial-thromboplastin-time-ptt-test/. Accessed January 2020.
2. https://medlineplus.gov/lab-tests/coagulation-factor-tests/. Accessed January 2020.
3. https://www.merckmanuals.com/en-ca/home/blood-disorders/blood-clotting-process/how-blood-clots. Accessed January 2020.
4. https://emedicine.medscape.com/article/2085837-overview#a4. Accessed January 2020.
5. https://www.nhlbi.nih.gov/health-topics/bleeding-disorders. Accessed January 2020.
6. https://www.ncbi.nlm.nih.gov/books/NBK507772/. Accessed January 2020.
7. https://www.hemophilia.org/sites/default/files/document/files/Nurses-Guide-Chapter-1-Introduction-to-Bleeding-Disorders.pdf. Accessed January 2020.
8. https://www.medicine.mcgill.ca/physio/vlab/bloodlab/PT_PTT.htm. Accessed January 2020.
9. https://www.cdc.gov/ncbddd/hemophilia/facts.html. Accessed January 2020.
10. https://www.cdc.gov/ncbddd/vwd/facts.html. Accessed January 2020.
11. https://www.cdc.gov/ncbddd/hemophilia/treatment.html. Accessed January 2020.
12. https://medlineplus.gov/ency/article/000573.htm. Accessed January 2020.
13. https://www.nhlbi.nih.gov/health-topics/disseminated-intravascular-coagulation. Accessed January 2020.
14. https://www.cdc.gov/ncbddd/vitamink/facts.html. Accessed January 2020.