There are various clotting factors in the body that work together to stop bleeding and play a role in the clotting process. A problem with any one of these factors can lead to prolonged bleeding time—the time required for a clot to form. The aPTT test is used to determine how well specific clotting factors are functioning. It is known as a screening test that checks for deficiencies in all clotting factors except factors VII and XIII.
It is generally performed in conjunction with a different blood test known as the prothrombin time (PT) test. The prothrombin time (PT) test is a different test that measures the blood’s ability to clot and is particularly sensitive to Factor VII.
The PTT test is a blood test used to measure the time it takes for blood to clot. A variant of this test, known as aPTT, measures the same time but involves adding a substance to liquid blood to induce faster clotting. Blood contains various clotting factors in different amounts. If there is a deficiency or defect in any of these factors, blood clotting may take longer than normal. This test helps monitor the function of these clotting factors.
What Is the aPTT Test Used For?
The aPTT is a blood test that determines the time it takes for blood to clot. The aPTT test is performed for the following purposes:
To assess the function of specific clotting factors: If one of these factors is deficient or defective, the individual may have a bleeding disorder. Hemophilia is one such disorder.
To check for problems with the immune system: Certain autoimmune disorders that cause the immune system to attack clotting factors manifest as clotting problems.
To monitor patients who require heparin: In some conditions, the blood forms clots at a rate higher than normal. Abnormal clots that form outside of this context can block blood vessels, leading to serious health problems such as heart attacks or strokes. Heparin is generally used to prevent the formation of these abnormal clots. However, using more heparin than necessary can lead to severe and potentially life-threatening bleeding. For this reason, the aPTT test should be used to monitor clotting time and adjust the dosage accordingly.
When Is the aPTT Test Performed?
This test may be needed if a healthcare professional suspects a problem with one or more clotting factors. For example, if a bleeding disorder such as von Willebrand disease is present, or if there is another condition that prevents the blood from clotting, this test helps determine the source of the problem. The aPTT test may be required in the following situations:
- Unexplained heavy bleeding
- Minor bleeding, bruising, or the formation of hematomas
- Blood in the stool or urine
- Minor bleeding from the gums
- Menstrual cycles accompanied by heavy bleeding in women
- Joint pain and swelling
- Persistent, hard-to-stop nosebleeds
- Formation of a clot inside a blood vessel
What Is a Low aPTT?
It is rare for PTT or aPTT values to fall below the normal reference range. Therefore, it is recommended that a new test be performed to rule out the possibility of heparin contamination of the blood sample or any other measurement error.
What Is a High aPTT?
When the aPTT value—which is normally considered to fall within the reference range of 26 to 35—reaches 100 or higher, bleeding occurs in the body. This condition, which causes impaired clotting, results in severe bleeding or delayed clotting.
What Should a Normal aPTT Value Be?
Normal reference ranges vary depending on the laboratory. Therefore, it is necessary to consult a specialist to understand what these values mean. A typical PTT value is 60 to 70 seconds. aPTT measures the same thing, but in this test, a substance is added to the blood to accelerate clotting. The normal range for aPTT is 25 to 35 seconds. If the test is performed because the patient is taking heparin, the PTT range is 120 to 140 seconds, while the aPTT should be between 60 and 80 seconds.
How Is the aPTT Test Performed?
Like most other blood tests, the aPTT test is performed using a blood sample drawn from a vein with a syringe. Blood is generally drawn from a vein located on the underside of the elbow or on the back of the hand. The blood sample is sent to the laboratory in a tube with a blue cap.
What Are the Symptoms of Elevated aPTT?
Many findings are examined during blood tests. One of the conditions assessed during a blood test is the aPTT result. Some of the symptoms of elevated aPTT are as follows:
- Recurrent bleeding episodes
- Easy bruising
- Blood in the stool or urine
- Recurrent bleeding from the gums
- Heavy menstrual bleeding in women
- Pain and swelling in the joints
- Recurrent, prolonged nosebleeds
Under What Circumstances Does a Prolonged aPTT Occur, and What Are the Symptoms?
These conditions include recurrent miscarriages, leukemia, malnutrition, various liver disorders, liver problems, and severe blood loss during childbirth. Additionally, the aPTT time is prolonged in cases of disseminated intravascular coagulation (DIC).
Applications of the aPTT Test
The aPTT test is used to monitor the time it takes for a clot to form, which helps in adjusting medication dosages.
This test has several applications. These can be listed as follows:
- Evaluation of the coagulation system
- Monitoring anticoagulant therapy and adjusting medication dosage
- Screening for blood clotting
- Investigation of liver failure
- Evaluation of vitamin K deficiency