Activated Partial Thromboplastin Time (APTT)

What sample is needed for Activated Partial Thromboplastin (APTT)?

1. The blood is carefully collected in an anticoagulant with a fixed ratio.
   • Take 0.2 ml anticoagulant (ESR solution may be used) and 1.8 ml whole blood.
2. Draw blood from a 3.2% buffered citrated tube with a 9:1 = blood: citrate ratio.
   1. Citrate binds calcium and prevents coagulation.
3. The APTT sample may be taken 30 to 60 minutes before the next dose of Heparin.

What are the precautions for Activated Partial Thromboplastin (APTT)?

1. Plasma is stable for one hour at 4 °C and 28 days if frozen.
2. Sample handling is very critical. If the blood and anticoagulant ratio is incorrect, then the results are false and raised.

What are the Indications for Activated Partial Thromboplastin (APTT)?

1. APTT is used to monitor the heparin therapy.
2. This is used for the diagnosis of bleeding disorders.
3. APTT may be used to check treatment for patients taking Heparin or other blood-thinning medicines.
4. APTT measures the intrinsic system and common pathways.
5. APTT detects the functioning of factors XII, XI, X, IX, VII, V, II, and I (12, 11, 10, 9, 7, 5, 2, 1).
6. For the diagnosis of Hemophilia and Christmas disease.
7. APTT evaluates all coagulation factors except factors VII and XIII.
8. PT is advised to monitor the extrinsic pathway.
   1. PT is also advised to monitor the warfarin therapy.
   2. PT also advised detecting factor VII deficiency.

What is the principle of Activated Partial Thromboplastin (APTT)?

1. The PTT is a one-stage test.
2. PTT evaluates Factor I (Fibrinogen), Factor II (prothrombin), Factor V, VIII, XI, X, XI, and XII (5, 8, 9, 10, 12) http://Blood Coagulation Factors.
3. The partial thromboplastin time (PTT) and Activated Partial thromboplastin time (APTT) are for the same function, but APTT is a more sensitive version of PTT.

How will you define PTT and APTT?

The PTT is a one-stage clotting test.

1. It screens for coagulation disorders.
2. It can detect the deficiency of the intrinsic thromboplastin system.
3. It also detects any deficiency of the extrinsic coagulation pathway.

Activated Partial Thromboplastin (APTT):

1. APTT is PTT, but with the addition of an activator, the time for the clot formation is decreased.
2. APTT is more sensitive than PTT.

What is detected by the Activated Partial Thromboplastin (APTT)?

1.  Deficiency of the intrinsic pathway.
2. Incubating anticoagulants.
3. Monitor heparin therapy.
4. It is part of the coagulation panel.

What are the theories of coagulation?

1. To understand the basis of the PTT and APTT, we have to have the concept of the process of coagulation.
2. In 1905 – 1906, P. Morowitz published the theory of blood coagulation. This was unchanged for 40 years. He divided coagulation into two phases.

3. Modern theory divided this process into three stages.

How is the coagulation cascade run?

1. PTT was useful in detecting intrinsic factor abnormalities, but it was relatively insensitive to the effect of heparin.
   1. However, APTT was sensitive to the heparin effect.
   2. The APTT was sensitive to coagulation factors deficiency within the intrinsic pathway before the prothrombin was converted to thrombin.

What are the indications for PTT?

1. Detect the Intrinsic thromboplastin system.
2. Detects Common Pathway.
3. Factor I (fibrinogen), Factor II (prothrombin), V, VIII, IX, X, XI, and XII.
4. Detects extrinsic coagulation.
5. It is a one-stage clotting test.

What is the significance of PTT?

1. In Hemophilia, PTT is prolonged.
2. Coagulation factors are synthesized in the liver, so in liver diseases, they are decreased.
3. PTT is prolonged in the abnormality of the deficiency of factors I, II, VII, XII, X, XI,  and XII.

Prothrombin time (PT):

How will you define prothrombin time (PT)?

1. Prothrombin is a protein produced by the liver.
2. Prothrombin production is dependent upon an adequate amount of vitamin K.
3. It is one of the important screening tests for coagulation abnormality.

What are the indications for Prothrombin time (PT)?

1. It measures potential defects in stage II of coagulation, extrinsic pathway.
2. To monitor anticoagulant therapy with Coumadin.
3. It is advised for coagulation disorder.
4. It may be part of liver functions.

What are the contents of prothrombin time (PT) reagents?   

1. The plasma of the patient.
2. Complete tissue thromboplastin (this will activate the extrinsic coagulation system). 
3. Phospholipids act as platelet substitutes.
4. CaCl₂.

What is the significance of prothrombin time (PT)?

1. The PT test measures factors of extrinsic and common pathways (VII, X, V, II, and I).
2. Factor VII is listed as the extrinsic system.
3. Common pathways have the factors X, V, II, and I.
4. PT  test is ideal to detect early vitamin K deficiency.
5. PT also monitors oral anticoagulant therapy.
6. In case of severe fibrinogen deficiency, it produces an abnormal PT test.
7. PT does not detect deficiency of factors XII, XI, IX, VIII, or XIII.

What is the normal value of PTT and APTT

Source 1

• Varies from lab to lab.
• Normal control is always run with the patient sample.
• In general, it is <35 seconds.
  • PTT: 60 to 70 seconds.
  • APTT: 30 to 40 seconds.
• If APTT is less than 50 seconds, then the therapeutic goal is not achieved, and the Heparin dose may increase.
  • When APTT is greater than 100 seconds is risky for the patient, and there are chances of spontaneous bleeding.
• Panic value Usually, it is considered above 70 seconds.
  • Heparin’s effect is immediate and short-lived as compared to warfarin.

Source 2

• APTT = 30 to 40 seconds
• PTT = 60 to 70 seconds
• PT   = 11.0 to 13.0 seconds
• Possible critical values
  • APTT = >70 seconds
  • PTT = > 100 seconds

What are the causes of increased APTT value?

1. All congenital deficiencies (Intrinsic system coagulation factors).
2. Cirrhosis.
3. Disseminated intravascular coagulopathy (DIC ).
4. Fibrin breakdown products.
5. Factor XII deficiency.
6. Hemophilia A and B.
7. Hypofibrinogenemia.
8. Malabsorption.
9. Von Willebrand’s disease.
10. Vit K deficiency.
11. Fibrin breakdown products.
12. Leukemia.
13. Drugs.
14. Heparin therapy.
15. Warfarin therapy.
16. In the case of streptokinase and urokinase.
17. Circulating anticoagulant inhibitors. These may be specific for factor VIII.
    1. These are seen as anti-factor VIII and anti-factor IX in 5% to 10% of hemophilic patients.
    2. These are also in multiple plasma transfusions.
    3. Drug reactions.
    4. In the case of tuberculosis.
    5. In autoimmune diseases like SLE and rheumatoid arthritis.

What are the PT and APTT levels in various diseases?

What is the value of these tests for laymen?

1. This test is advised for patients treated with Heparin or blood-thinning drugs.
2. PTT and INR also have been done in patients with blood-thinning drugs (warfarin).

• For more information, please see PT and PTT.

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