Test Detail
Overview
Interpreting Results
FAQ's

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Written by
Dr. Shreya Gupta
BDS, MDS - Oral and Maxillofacial Pathology
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MBBS, MD (Pharmacology)
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Activated Partial Thromboplastin Time

(aPTT)
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Activated Partial Thromboplastin Time
You need to provide
Blood
This test is for
Male, Female
Test Preparation
  1. No special preparation required

Overview


What is aPTT?

The Activated Partial Thromboplastin Time (aPTT) test measures the time taken by the blood to form a clot after the addition of substances (reagents) which activate the clot formation. The aPTT test is performed to detect a bleeding or clotting disorder and to monitor the treatment with anticoagulant medication (blood thinning medicine) like heparin.

Why is aPTT done?

 

The Activated Partial Thromboplastin Time Test is performed:

·         To detect and diagnose bleeding or clotting disorder

·         Before performing a surgical procedure to assess the risk of bleeding

·         To monitor the treatment with blood-thinning medicines (e.g. unfractionated heparin therapy)

·         To investigate the cause of thrombotic episodes or recurrent miscarriages



What does aPTT Measure?

The Activated Partial Thromboplastin Time (aPTT) test measures the time taken by the blood to form a clot after the addition of substances (reagents) which activate the clot formation.

In case of any bleeding, the body responds to stop the blood loss as quickly as possible by forming a blood clot. This process of blood clotting or coagulation is called hemostasis and involves a series of chemical reactions in the blood (coagulation cascade). During this process, the blood proteins called coagulation factors get activated one after another in a series. The activated coagulation factors lead to the formation of fibrin mesh around the platelets and other blood cells at the site of bleeding and this complex hardens to form a “blood clot”.

Coagulation cascade proceeds by two pathways, the intrinsic pathway, and the extrinsic pathway. These pathways later merge together into a common pathway. The Activated Partial Thromboplastin Time (aPTT) test measures the functioning of Blood Coagulation Factors I, II, V, XII, VIII, IX, X, and XI, along with other factors Prekallikrein (PK), and High Molecular Weight Kininogen (HK) which form parts of the intrinsic and common coagulation pathways.

The Activated Partial Thromboplastin Time (aPTT) test measures the time taken by the blood to form a clot after the addition of substances (calcium and phospholipid emulsion) which activate clotting. The aPTT test result is compared to a control sample of normal blood.

The aPTT test is usually performed along with Prothrombin Time (PT) test to evaluate the cause of a coagulation defect, if any. PT test assesses the functioning of Blood Coagulation Factors I, II, V, VII, and X, which are parts of the extrinsic and common pathways by measuring the time taken for conversion of prothrombin to thrombin.


Interpreting aPTT results


Interpretations

Normal Reference Ranges:

Activated Partial Thromboplastin Time (aPTT):  30 - 40 seconds

In case the patient is receiving treatment with Heparin, the dose is adjusted so that the aPTT result is about 1.5 to 2.5 times the normal value.

Causes of prolonged aPTT are:

  • Inherited coagulation factor deficiencies seen in conditions like von Willebrand disease, Hemophilia A and Hemophilia B (Christmas disease) etc.

  • Acquired Coagulation factor deficiencies due to liver disease, deficiency of Vitamin K etc.

  • Presence of inhibitors, such as lupus anticoagulant and anticardiolipin antibodies, which bind to phospholipids present on the surface of platelets

  • Disseminated intravascular coagulation (DIC)

  • Leukemia


Causes of shortened aPTT are:

  • Disseminated intravascular coagulation (in early stages)

  • Extensive cancer (eg, ovarian, pancreatic, colon cancer)


The PT and aPTT tests are usually performed and evaluated simultaneously, and the results may be interpreted as follows:

PT RESULT

aPTT RESULT

CONDITIONS INDICATED

High

Normal

Liver diseases, Vitamin K deficiency, reduced activity of Factor VII, Disseminated Intravascular Coagulation (DIC), Warfarin treatment

Normal

High

Reduced activity of Factors VIII, IX, XI, or XII, von Willebrand disease, autoantibodies destroying one or more coagulation factors

High

High

Reduced activity of Factors I, II, V or X, liver diseases, DIC, an overdose of Warfarin

Normal

Normal

Normal hemostasis usually. However, normal results may also appear in a mild reduction in coagulation factor activity and mild cases of von Willebrand disease.



Answers to Patient Concerns & Frequently Asked Questions (FAQs) about aPTT


Frequently Asked Questions about Activated Partial Thromboplastin Time

Q. How is this test performed?
This test is performed on a blood sample. A syringe with a fine needle is used to withdraw blood from a blood vessel in your arm. The healthcare provider will tie an elastic band around your arm to make the blood vessels swell with blood. This makes it easier to withdraw blood. You may be asked to tightly clench your fist. Once the veins are clearly visible, the area is cleaned with an antiseptic solution and then the needle is inserted into the blood vessel to collect the sample. You will feel a tiny pinprick during the procedure. Blood sample once collected will then be sent to the laboratory.
Q. Is there any risk associated with this test?
There is no risk associated with the test. However, since this test involves a needle prick to withdraw the blood sample, in very rare cases, a patient may experience increased bleeding, hematoma formation (blood collection under the skin), bruising or infection at the site of needle prick.
Q. What diseases can affect blood clotting to cause bleeding disorders?
Certain inherited conditions and diseases that can cause bleeding disorders include: · Hemophilia · Clotting factor deficiency · Vitamin K deficiency · Liver diseases · Bone marrow disorders · von Willebrand disease · Immune system diseases · Cancers like leukaemia
Q. What are some apparent symptoms of bleeding or clotting disorders?
Visible signs of bleeding or clotting disorders include: · Unexplained heavy bleeding · Abnormal menstrual bleeding in women · Bruising and bleeding easily · Frequent nosebleeds · Bleeding gums · Repeated heart attacks or strokes
Q. Is there any preparation required before the aPTT test?
Inform the doctor of any medications you may be taking as certain medications like antihistamines, warfarin, herbal medicines, etc. can affect the test results. In case of a patient who is receiving heparin therapy by intermittent injection, the sample should be taken 30-60 minutes before the next dose of heparin. Whereas the sample can be drawn at any time in a patient receiving a continuous heparin infusion. No other specific preparations are usually required before the aPTT test.
Q. What factors can affect the aPTT test results?
Certain medications like antihistamines, ascorbic acid, chlorpromazine, heparin, Vitamin K supplements and salicylates may affect the test results. A high temperature can also alter the result.
Q. What additional tests can be prescribed by your doctor in case of abnormal aPTT test result?
Additional tests that may be prescribed in case of abnormal aPTT test result are: · Platelet Count · Thrombin Time Test · Prothrombin Time Test (PT) · Heparin Neutralization Assay · Fibrinogen Test · Coagulation Factor Tests · von Willebrand Factor Test · Liver Function Test (LFT)
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