Aptt
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| Purpose | Evaluate the intrinsic and common coagulation pathways |
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The Activated Partial Thromboplastin Time (aPTT) is a medical test that characterizes blood coagulation. It is used primarily to investigate unexplained bleeding or clotting and to monitor patients on heparin therapy.
Overview[edit | edit source]
The aPTT test measures the time it takes for a clot to form in a blood sample after reagents are added. It evaluates the function of the intrinsic pathway and the common pathway of the coagulation cascade. The test is sensitive to deficiencies in clotting factors such as Factor VIII, Factor IX, Factor XI, and Factor XII.
Clinical Significance[edit | edit source]
The aPTT is an essential test in the diagnosis and management of bleeding disorders. It is often used in conjunction with the prothrombin time (PT) test to provide a comprehensive assessment of the coagulation system.
Indications[edit | edit source]
- Monitoring of unfractionated heparin therapy
- Evaluation of bleeding disorders
- Preoperative screening
- Investigation of recurrent miscarriages
Interpretation[edit | edit source]
A prolonged aPTT may indicate:
- Deficiency of one or more clotting factors
- Presence of an inhibitor such as lupus anticoagulant
- Heparin therapy
- Liver disease
- Vitamin K deficiency
A shortened aPTT is less common and may be seen in:
- Disseminated intravascular coagulation (DIC)
- Extensive cancer
Procedure[edit | edit source]
The aPTT test is performed by collecting a blood sample in a tube containing an anticoagulant, usually citrate. The sample is then centrifuged to separate the plasma, which is used for the test. Reagents, including a phospholipid and an activator such as kaolin or silica, are added to the plasma. Calcium chloride is then added to initiate clotting, and the time taken for clot formation is measured.
Factors Affecting aPTT[edit | edit source]
Several factors can influence the results of an aPTT test:
- Anticoagulant therapy
- Liver function
- Vitamin K levels
- Fibrinogen levels
- Presence of inhibitors
Limitations[edit | edit source]
The aPTT test has limitations and may not detect mild deficiencies of certain clotting factors. It is also affected by the presence of lupus anticoagulant, which can prolong the aPTT without causing bleeding.
Related Tests[edit | edit source]
- Prothrombin time (PT)
- Thrombin time (TT)
- Fibrinogen level
- D-dimer test
See Also[edit | edit source]
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Contributors: Prab R. Tumpati, MD
