Activated Partial Thromboplastin Time (APTT)

Sample for Activated Partial Thromboplastin

1. The blood is collected in an anticoagulant with a fixed ratio carefully.
   • Take 0.2 ml anticoagulant (ESR solution may be used) and 1.8 ml whole blood.
2. Can draw the 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 min before the next dose of Heparin.

Precautions for Activated Partial Thromboplastin

1. Plasma is stable for one hour at 4 °C and 28 days if frozen.
2. Sample handling is very critical. If the ratio of blood and anticoagulant is not correct, then the results are false and raised.

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.

Purpose of the test (Indications)

1. This is used for the diagnosis of bleeding disorders.
2. APTT may be used in the patient to check treatment for those who are taking Heparin or other blood-thinning medicines.
3. APTT measures the intrinsic system and common pathways.
4. APTT detects the functioning of factors XII, XI, X, IX, VII, V, II, and I (12, 11, 10, 9, 7, 5, 2, 1).
5. For the diagnosis of Hemophilia and Christmas disease.
6. APTT evaluates all coagulation factors except factors VII and XIII.
7. 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.

Definition of 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, which decreases the time for the clot formation.
2. APTT is more sensitive than PTT.

The Activated Partial Thromboplastin (APTT) detects:

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

Summary of the Coagulation process:

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.

Activated Partial Thromboplastin Time (APTT): Coagulation phases

3. Modern theory divided this process into three stages.

Activated Partial Thromboplastin Time (APTT): Coagulation modern theory

4. The coagulation cascade is as follows:

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 very sensitive to coagulation factors deficiency within the intrinsic pathway before the prothrombin was converted to thrombin.
2. Detect the Intrinsic thromboplastin system.
3. Detects Common Pathway.
4. Factor I (fibrinogen), Factor II (prothrombin), V, VIII, IX, X, XI, and XII.
5. It is a one-stage clotting test.
6. Detects extrinsic coagulation.

Prothrombin time (PT) is advised for:

1. Prothrombin is a protein produced by the liver. Prothrombin production is dependent upon an adequate amount of vitamin K.
2. It is one of the important screening tests for coagulation abnormality. It measures potential defects in stage II of coagulation, extrinsic pathway.
3. To monitor anticoagulant therapy with Coumadin.
4. It is advised for coagulation disorder.
5. It may be part of liver functions.

PT reagents contain:   

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

PT test significance is:

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.

Principle of Prothrombin test (PT) reaction

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

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 dose of Heparin may be increased.
  • 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

Abnormal High results of APTT are due to:

1. All congenital deficiencies of Intrinsic system coagulation factors.
2. Cirrhosis.
3. Disseminated intravascular coagulopathy (DIC ).
   1. Fibrin breakdown products.
4. Factor XII deficiency.
5. Hemophilia A and B.
6. Hypofibrinogenemia.
7. Malabsorption.
8. Von Willebrand’s disease.
9. Vit K deficiency.
10. Fibrin breakdown products.
11. Leukemia.
12. Drugs.
13. Heparin therapy.
14. Warfarin therapy.
15. In the case of streptokinase and urokinase.
16. 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.

Differential diagnoses of bleeding disorders (What is a normal PT aPTT level?):

Test value for the layman:

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

• Please, for more information, see PT and PTT.

Questions and answers: