APTT, which is the coalin-kephalin time (or the time of partial thromboplastin after activation) - it is one of the indicators of blood clotting. When is APTT tested? What are the standards? What may be indicated by the extension or reduction of the coaline-kephalin time?

APTT , i.e.Coalin-Cephalin Time(akaActivated Partial Thromboplastin Time ) is a measure of the activity of factors XII, XI, IX and VIII, which make up the endogenous system, and is also dependent on factors involved in the formation of thrombin (prothrombin, factors X and V) and the conversion of fibrinogen to fibrin. Proper hemostasis of the body protects it against blood loss in the event of a break in the continuity of blood vessels. Maintaining proper hemostasis depends on the proper interaction of proteins from the coagulation system, the fibrinolytic system, as well as blood vessels and platelets.

APTT, which is the coalin-kephalin time (or the time of partial thromboplastin after activation) - it is one of the indicators of blood clotting. Human blood clotting can take two pathways, known as the extrinsic and intrinsic systems. Each pathway, by activating individual plasma coagulation factors, converts prothrombin to thrombin and then fibrinogen to fibrin (the common part of the clotting path).

What is APTT used for?

The primary use of APTT is to monitor anticoagulant therapy with unfractionated heparin. The correct therapeutic heparin concentration in the blood should cause a 1.5-2.5-fold prolongation of APTT compared to the reference value, i.e. during APTT treatment it should be 60-90 s. Coalin-kephalin time is also prolonged during treatment with other anticoagulants, such as hirudin derivatives and argatroban. This indicator is not intended to monitor LMWH treatment. Another application of APTT is the diagnosis of congenital and acquired bleeding disorders.

What are the standards?

The correct APTT value is 26-40 s (this value depends on the reagents used and may differ between laboratories).

What does APTT extension mean?

Prolongation of APTT means decreased activity of plasma coagulation factorsblood:

  • deficiency of factors VIII (hemophilia A), IX (hemophilia B), XI (hemophilia C) and factor X and prothrombin
  • deficiency, no fibrinogen
  • von Willebrand disease
  • disseminated intravascular coagulation (DIC) syndrome - in which clotting factors are consumed as a result of the formation of both hemorrhages and blood clots
  • deficiency of macromolecular kininogen (supports the activation of factor XII, XI and precalikrein) and prekalikrein (activates factor XII)
  • factor XII deficiency
  • congenital or acquired V factor deficiency

In addition, this test is applicable to:

  • liver damage is suspected - liver disease may have an effect on the coagulation system
  • suspected vitamin K deficiency - takes part in maintaining the correct concentration of coagulation factors: II, VII, IX, X and proteins that inhibit blood clotting: proteins C and S, and regulates the production of prothrombin
  • monitoring of unfractionated heparin anticoagulation. Heparin is an anticoagulant drug given into a vein or by injection. Treatment with it must be closely monitored, as giving too much may cause a hemorrhage, and too little will not prevent blood clots.
  • monitoring of treatment with oral anticoagulants
  • to detect non-specific antibodies, such as lupus anticoagulant, that are associated with thrombotic events and repeated episodes of miscarriage. For this purpose, APTT can be performed in the coagulation test panel as an aid in determining the cause of miscarriages or diagnosing the antiphospholipid syndrome
  • Based on a thorough history, APTT and PT are sometimes performed prior to surgery or other invasive procedures to assess bleeding tendency.

Following or with abnormal APTT results, the following tests are performed: platelet count (should be monitored during treatment with heparin), thrombin time, fibrinogen (to rule out fibrinogen deficiency as the cause of APTT prolongation), coagulation factors, von Willebrand factor test (to determine if the prolongation of APTT is due to von Willebrand disease).

Shortening of APTT can occur in hypercoagulable states, but has no diagnostic significance. Abnormal APTT values ​​may be due to improper storage of the blood or plasma sample prior to this test.

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