Coagulation:- part 6 – Activated Partial Thromboplastin Time (APTT), Partial thromboplastin time (PTT), Prothrombin time (PT) and INR
- 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.
- The APTT sample may be taken 30 to 60 min before the next dose of Heparin.
- Plasma is stable for one hour at 4 °C and 28 days if frozen.
- Sample handling is very critical. If the ratio of blood and anticoagulant is not correct, then the results are false and raised.
- The PTT is a one-stage test.
- 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.
- 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)
- This is used for the diagnosis of bleeding disorders.
- APTT may be used in the patient to check treatment who are taking Heparin or other blood-thinning medicines.
- APTT measures the intrinsic system and common pathways.
- APTT detects the functioning of factors XII, XI, X, IX, VII, V, II, and I (12, 11, 10, 9, 7, 2, 1).
- For the diagnosis of Hemophilia and Christmas disease.
- To understand the basis of the PTT and APTT, we have to have the concept of the process of coagulation.
- In 1905 – 1906 P. Morowitz published the theory of blood coagulation. This was unchanged for 40 years. He divided coagulation into two phases.
- Modern theory divided this process into three stages.
- The coagulation cascade is as follows:
The intrinsic pathway consists of:
- Vessel injury.
- Collagen contacts.
- Factors X11, X1, 1X, V111, and Calcium.
The extrinsic pathway consists of:
- Vessel injury.
- Tissue factor.
- Factor VII.
The common pathway consists of:
- Factor X.
- Prothrombin converted to Thrombin.
- Factor XIII.
- Fibrinogen converted to fibrin.
- Fibrin forms the stable clot.
Bleeding disorders have different presentations because of the etiology like:
- Platelets disorders give rise to:
- There is bleeding from the mucous membranes,
- Coagulation factors deficiency leads to:
- Deep hematomas.
- There is bleeding into the joints.
- There is hematuria.
- Bleeding disorders may be due to:
- Defects in the vascular system.
- Platelets disorders.
- Coagulation factors deficiency.
- Specific inhibitors.
- Fibrinolytic disorders.
Partial thromboplastin time (PTT):
- PTT was useful in detecting intrinsic factors abnormalities, but it was relatively insensitive to the effect of heparin.
- But APTT was sensitive to the heparin effect.
- The APTT was very sensitive to coagulation factors deficiency within the intrinsic pathway before the prothrombin is converted to thrombin.
- Detect the Intrinsic thromboplastin system.
- Detects Common Pathway.
- The factor I (fibrinogen), Factor II (prothrombin), V, VIII, IX, X, XI, and XII.
- It is one stage clotting test.
- Detects in the extrinsic coagulation.
Activated partial thromboplastin time (APTT):
- APTT is very sensitive to coagulation factors deficiencies within the intrinsic pathway before the prothrombin to thrombin stage.
- Intrinsic pathway.
- Monitor heparin therapy.
Prothrombin time (PT) is advised for:
- To monitor anticoagulant therapy with coumadin.
- It is advised for coagulation disorder.
- It may be part of liver functions.
PT reagents contain:
- The plasma of the patient.
- Complete tissue thromboplastin ( this will activate the extrinsic coagulation system).
- Phospholipids act as a platelet substitute.
- PT test significance is:
- The PT test measures factors of extrinsic and common pathways (VII, X, V, II, and I).
- Factor VII is listed as the extrinsic system.
- Common pathways have the factors X, V, II, and I.
- PT test is ideal to detect early vitamin K deficiency.
- PT also monitors oral anticoagulant therapy.
- In case of severe fibrinogen deficiency, it produces an abnormal PT test.
APTT reagent contains:
- phospholipids substitute, activator.
- CaCl2 initiates fibrin clot.
- APTT test significance is:
- PTT is used to detect coagulation disorder and specifically detect the deficiency of the intrinsic thromboplastin system and also find the defect in the extrinsic pathway.
- APTT detects the intrinsic pathway and common pathway deficiency (XII, XI, IX, VIII, X, II, and I).
- PT and APTT both abnormalities will tell us common pathways (X, V, II, and I)
- In Hemophilia PTT is prolonged.
- Coagulation factors are synthesized in the liver so liver diseases are decreased.
- PTT is prolonged in the abnormality of the deficiency of factors I, II, VII, XII, X, XI, and XII.
- Varies with the lab to lab.
- Normal control is always run with the patient sample.
- In general, 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 for spontaneous bleeding.
- Panic value Usually it is considered above 70 seconds.
- Heparin effect is immediate and short-lived as compared to warfarin.
- APTT = 30 to 40 seconds
- PTT = 60 to 70 seconds
- Possible critical values
- APTT = >70 seconds
- PTT = > 100 seconds
Abnormal High results are due to:
- All congenital deficiencies of Intrinsic system coagulation factors.
- Disseminated intravascular coagulopathy (DIC ).
- Factor XII deficiency.
- Hemophilia A and B.
- Von Willebrand’s disease.
- Vit K deficiency.
- Fibrin breakdown products.
International normalized ratio = INR
- This is the ratio of the patient’s prothrombin time (PT) and the normal mean PT time raised to the power of the international sensitivity index.
- This is done for routine health screenings.
- To evaluate the medical condition is improving or worsening.
- To assess to measure the success or failure of a medication or treatment plan.
Purpose of the INR
- This is done to evaluate the following conditions:
- Antiphospholipid syndrome
- Atrial fibrillation
- Heart valve replacement (prosthesis).
- Some cases of heart failure (Cardiomyopathy).
- Venous thromboembolism.
- The INR test result is given as a number.
- INR = 1 represents equal to normal clotting time.
- INR = 2 represents twice the normal clotting time.
- Normal value =1.0 to 1.5
- Critical value = > 5.5
- DVT patient on warfarin treatment = Expected range of INR is 2.0 to 3.0
Table showing the required value of INR in various diseases.
|Disease||Required INR value|
|Atrial fibrillation||2.0 to 3.0|
|Prosthetic valve prophylaxis||3.0 to 4.0|
|Pulmonary embolism||2.5 to 3.5|
|Orthopedic surgery||2.0 to 3.0|
|Deep vein thrombosis||2.0 to 3.0|
|Deep vein thrombi. prophylaxis||1.5 to 2.0|
Test value for the layman:
- This test is advised in the case of patients with the treatment of Heparin or blood-thinning drugs.
- PTT and INR also have been done in patients with blood-thinning drugs (warfarin).
- Please for more information see PT and PTT.