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Coagulation:- part 6 – Activated Partial Thromboplastin Time (APTT), Partial thromboplastin time (PTT), Prothrombin time (PT)

September 20, 2022HematologyLab Tests

Table of Contents

  • Activated Partial Thromboplastin Time (APTT)
      • Sample
        • Precautions
        • Principle of APTT
        • Purpose of the test (Indications)
      • Definition of PTT and APTT
      • Summary of the Coagulation process:
      • Bleeding disorders have different presentations because of the etiology like:
    • Activated partial thromboplastin time (APTT):
      • APTT reagent contains:
    • Partial thromboplastin time (PTT):
    • Prothrombin time (PT) is advised for:
      • PT reagents contain:   
      • The normal value of PTT and APTT
        • Abnormal High results of APTT are due to:
        • Differential diagnoses of bleeding disorders:
        • Test value for the layman:

Activated Partial Thromboplastin Time (APTT)

Sample

  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 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

  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 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 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 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.

The 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.
    Coagulation phases

    Coagulation phases

  1. Modern theory divided this process into three stages.
    Coagulation modern theory

    Coagulation modern theory

  1. The coagulation cascade is as follows:
Blood coagulation process: Coagulation pathways

Blood coagulation process: Coagulation pathways

Summary of the coagulation pathways

Summary of the coagulation pathways

Bleeding disorders have different presentations because of the etiology like:

  1. Platelets disorders give rise to:
    1. Petechiae.
    2. There is bleeding from the mucous membranes,
  2. Coagulation factors deficiency  leads to:
    1. Deep hematomas.
    2. There is bleeding into the joints.
    3. There is hematuria.
  3. Bleeding disorders may be due to:
    1. Defects in the vascular system.
    2. Platelets disorders.
    3. Coagulation factors deficiency.
    4. Specific inhibitors.
    5. Fibrinolytic disorders.

Activated partial thromboplastin time (APTT):

  1. APTT is very sensitive to coagulation factors deficiencies within the intrinsic pathway before the prothrombin to thrombin stage.
  2. Intrinsic pathway.
  3. Monitor heparin therapy.

APTT reagent contains:

  1.  phospholipids substitute, activator.
  2. CaCl2 initiates fibrin clots.
  3. APTT test significance is:
    1. PTT is used to detect coagulation disorder, specifically detecting the deficiency of the intrinsic thromboplastin system and finding the defect in the extrinsic pathway.
    2. APTT detects the intrinsic pathway and common pathway deficiency (XII, XI, IX, VIII, X, II, and I).
    3. PT and APTT both abnormalities will tell us common pathways (X, V, II, and I).
  4. Advantages of APTT:
    1. APTT reproducibility is adequate where there is <10% variation.
    2. Its reaction is less (30 to 50 seconds).
    3. It is easy to perform.
    4. It can be used in automation.
  5. Disadvantages of APTT:
    1. Heparin above the required level causes APTT nonlinear and unreliable.
    2. Reagents from different companies produce different results, so not possible to compare the results.
    3. APTT is affected by warfarin.
Principle of APTT reaction

Principle of APTT reaction

Partial thromboplastin time (PTT):

  1. PTT was useful in detecting intrinsic factors abnormalities, but it was relatively insensitive to the effect of heparin.
    1. But 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 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.
  4. 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

Principle of Prothrombin test (PT) reaction

Fibrin clot formation depends upon the factors

Fibrin clot formation depends upon the factors

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

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:

APTT PT Platelets count Causes of bleeding disorders
Increased Normal Normal
  1. Heparin therapy
  2. Factor VIII, IX, and XI deficiencies
  3. Lupus anticoagulant
  4. von Willibrand’s disease
Normal Increased Normal
  1. Early coumadin therapy
  2. Factor VII deficiency or inhibitor
  3. Early vitamin K deficiency
  4. Early liver diseases
Increased Increased Normal
  1. Heparin therapy
  2. Coumadin therapy
  3. Malabsorption
  4. Liver diseases
  5. DIC (acute)
  6. Gall bladder diseases
Normal Normal Normal
  1. Chronic compensated DIC
  2. von Willebrand’s disease
  3. Factor XIII deficiency
  4. Aspirin
  5. Uremia
  6. Fibrinogen disorder (dysfibrinogenemia)
  7. Vasculitis
  8. Scurvy
  9. Colonic carcinoma
Normal Normal Increased
  1. Proliferative disorders
  2. CML
  3. Polycythemia rubra vera
  4. Essential thrombocythemia
Normal Normal Decreased
  1. Hemodilution
  2. Platelets disorders (destruction)
Increased Increased Decreased
  1. Acute DIC
  2. Liver diseases
  3. Heparin-induced thrombocytopenia
  4. Hypersplenism
  5. Thrombotic thrombocytopenic purpura
  6. Hemolytic uremic syndrome

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.

Possible References Used
Go Back to Hematology

Comments

Coagulation:- part 7 – Blood Coagulation Factors and Their descriptions – Labpedia.net Reply
November 7, 2021

[…] and APTT are prolonged in factor V […]

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