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Also known as: '''''coagulation profile — clotting profile — clotting tests — tests of haemostasis

Also known as: '''''coagulation profile — clotting profile — clotting tests — tests of haemostasis

[[Image:Coagulation Cascade.jpg|thumb|right|350px|oagulation cascade. Source: Wikimedia Commons; Author: Joe D (2007)]]

[[Image:Coagulation Cascade.jpg|thumb|right|350px|Coagulation cascade. Source: Wikimedia Commons; Author: Joe D (2007)]]

==Introduction==

==Introduction==

[[Image:LH_Platelet_Histology.jpg|thumb|right|<center><p>'''Platelets'''</p>^{©RVC 2008}</center>]]

[[Image:LH_Platelet_Histology.jpg|thumb|right|<center><p>'''Platelets'''</p>^{©RVC 2008}</center>]]

    

    

Abnormalities can develop in any of the components of haemostasis. Disorders of primary haemostasis include [[Haemorrhagic_Disease_Pathophysiology#Vascular_Fragility|vessel defects]] (i.e. vasculitis), [[Platelet_Abnormalities#Thrombocytopaenia|thrombocytopenia]] (due to decreased production or increased destruction) and [[Platelet Abnormalities|abnormalities in platelet function]] (e.g. congenital defects). These lead to the occurence of multiple minor bleeds and prolonged bleeding times; petechial or ecchymotic [[Haemorrhage - Pathology|haemorrhages]] may be seen for example, on the skin and mucous membranes, or ocular bleeds may arise. Generally, intact secondary haemostasis prevents major haemorrhage in disorders of primary haemostasis. When secondary haemostasis is abnormal, [[Haemorrhage - Pathology|larger bleeds]] are frequently seen. Haemothorax, haemoperitoneum, or haemoarthrosis may occur, in addition to subcutaneous and intramuscular haemorrhages. Petechiae and ecchymoses are not usually apparent, as intact primary haemostasis prevents minor capillary bleeding. Examples of secondary haemostatic disorders include [[:Category:Coagulation Defects|clotting factor deficiencies]] (e.g. hepatic failure, vitamin K deficiency, hereditary disorders) and circulation of substances inhibitory to coagulation (FDPs in [[Disseminated Intravascular Coagulation|disseminated intravascular coagulation]], [[Systemic Lupus Erythematosus|lupus]] anticoagulant). If fibrinolysis is defective, thrombus formation and infarctions may result. Thrombus formation may be promoted by vascular damage, circulatory stasis or changes in anticoagulants or procoagulants. For example, ATIII may be decreased. This can occur by loss due to glomerular disease or accelerated consumption in disseminated intravascular coagulation or sepsis.

Abnormalities can develop in any of the components of haemostasis. Disorders of primary haemostasis include [[Haemorrhagic_Disease_Pathophysiology#Vascular_Fragility|vessel defects]] (i.e. vasculitis), [[Platelet_Abnormalities#Thrombocytopaenia|thrombocytopenia]] (due to decreased production or increased destruction) and [[Platelet Abnormalities|abnormalities in platelet function]] (e.g. congenital defects). These lead to the occurence of multiple minor bleeds and prolonged bleeding times; petechial or ecchymotic [[Haemorrhage|haemorrhages]] may be seen for example, on the skin and mucous membranes, or ocular bleeds may arise. Generally, intact secondary haemostasis prevents major haemorrhage in disorders of primary haemostasis. When secondary haemostasis is abnormal, [[Haemorrhage|larger bleeds]] are frequently seen. Haemothorax, haemoperitoneum, or haemoarthrosis may occur, in addition to subcutaneous and intramuscular haemorrhages. Petechiae and ecchymoses are not usually apparent, as intact primary haemostasis prevents minor capillary bleeding. Examples of secondary haemostatic disorders include [[:Category:Coagulation Defects|clotting factor deficiencies]] (e.g. hepatic failure, vitamin K deficiency, hereditary disorders) and circulation of substances inhibitory to coagulation (FDPs in [[Disseminated Intravascular Coagulation|disseminated intravascular coagulation]], [[Systemic Lupus Erythematosus|lupus]] anticoagulant). If fibrinolysis is defective, thrombus formation and infarctions may result. Thrombus formation may be promoted by vascular damage, circulatory stasis or changes in anticoagulants or procoagulants. For example, ATIII may be decreased. This can occur by loss due to glomerular disease or accelerated consumption in disseminated intravascular coagulation or sepsis.

It is therefore important that all aspects of haemostasis can be independently evaluated. This will help to identify the phase affected and to pinpoint what the abnormality is. There are tests available to assess primary haemostasis, secondary haemostasis and fibrinolysis.

It is therefore important that all aspects of haemostasis can be independently evaluated. This will help to identify the phase affected and to pinpoint what the abnormality is. There are tests available to assess primary haemostasis, secondary haemostasis and fibrinolysis.

===Activated Clotting Time===

===Activated Clotting Time===

The activated clotting time (ACT) allows rapid evaluation of secondary haemostasis. The ACT is the time taken for 2ml of fresh whole blood to clot in a tube with a contact activator (diatomaceous earth²), but an automated analyser can perform a test with a similar principle. The reaction must occur at body temperature to give a reliable indication of haemostatic ability: this can be achieved by the use of a warm water bath, or by holding the tubes under an arm. The normal ACT is 90-120 seconds and less than 75 seconds in dogs and cats respectively².

The activated clotting time (ACT) allows rapid evaluation of secondary haemostasis. The ACT is the time taken for 2ml of fresh whole blood to clot in a tube with a contact activator (diatomaceous earth²), but an automated analyser can perform a test with a similar principle. The reaction must occur at body temperature to give a reliable indication of haemostatic ability: this can be achieved by the use of a warm water bath, or in an emergency by holding the tubes under an arm. The normal ACT is 90-120 seconds and <75 seconds in dogs and cats respectively².

The contact activator used in the ACT test triggers the intrinsic pathway, and so ACT allows assessment of the intrinsic and common pathways. ACT will therefore be prolonged when factors I, II, V, VIII, IX, X, XI or XII are deficient or abnormal, such as in DIC, liver disease, vitamin K antagonist toxicosis or haemophilia A or B². Thrombocytopenia may also increase ACT.

The contact activator used in the ACT test triggers the intrinsic pathway, and so ACT allows assessment of the intrinsic and common pathways. ACT will therefore be prolonged when factors I, II, V, VIII, IX, X, XI or XII are deficient or abnormal, such as in DIC, liver disease, vitamin K antagonist toxicosis or haemophilia A or B². Thrombocytopenia may also increase ACT.

===Activated Partial Thromboplastin Time===  

===Activated Partial Thromboplastin Time===  

The APTT is measures the time necessary to generate fibrin from activation of the intrinsic pathway³. It therefore assesses functionality of the components of the intrinsic and common pathways of coagulation. The test is performed on citrated plasma, and so blood should be collected into a sodium citrate tube if the APTT test is to be undertaken. Once a sample is obtained, factor XII is activated by an external agent that will not also activate factor VII, such as kaolin^{1, 3}. Since the intrinsic arm of the cascade requires platelet factors to function, the test also provides a phospholipid emuslion in place of these factors. Calcium is added, the preparation is incubated, and the time for clumping of kaolin is measured. Classically, partial thromboplastin time was measured after activation by contact with a glass tube, but use of an external activating agent in the newer, "activated" partial thromboplastin time method makes results more reliable³.

The APTT measures the time necessary to generate fibrin from activation of the intrinsic pathway³. It therefore assesses functionality of the components of the intrinsic and common pathways of coagulation. The test is performed on citrated plasma, and so blood should be collected into a sodium citrate tube if the APTT test is to be undertaken. Once a sample is obtained, factor XII is activated by an external agent that will not also activate factor VII, such as kaolin^{1, 3}. Since the intrinsic arm of the cascade requires platelet factors to function, the test also provides a phospholipid emuslion in place of these factors. Calcium is added, the preparation is incubated, and the time for clumping of kaolin is measured. Classically, partial thromboplastin time was measured after activation by contact with a glass tube, but use of an external activating agent in the newer, "activated" partial thromboplastin time method makes results more reliable³.

APPT evaluates the same pathways as ACT, and so will be prolonged by abnormalities or deficiencies in factors XII, XI, IX, VIII, X, V, II or I. However, APTT is not affected by thrombocytopenia and is also considered to be a more sensitive test than ACT: APTT becomes prolonged when 70% of a factor is depleted, compared to 90% depletion of ACT. APTT can also be prolonged in the presence of a circulating inhibitor to any of the intrinsic pathway factors. To differentiate factor deficiency from inhibition, a "mixing study" can be performed where the test is repeated on a 1:1 mix of patient and normal plasma. Complete correction indicates a deficiency, and partial or no resolution shows that an inhibitor is present. This difference stems from the above mentioned fact that the APTT will be normal in the presence of 50% normal activity³.

APPT evaluates the same pathways as ACT, and so will be prolonged by abnormalities or deficiencies in factors XII, XI, IX, VIII, X, V, II or I. However, APTT is not affected by thrombocytopenia and is also considered to be a more sensitive test than ACT: APTT becomes prolonged when 70% of a factor is depleted, compared to 90% depletion required to prolong the ACT. APTT can also be prolonged in the presence of a circulating inhibitor to any of the intrinsic pathway factors. To differentiate factor deficiency from inhibition, a "mixing study" can be performed where the test is repeated on a 1:1 mix of patient and normal plasma. Complete correction indicates a deficiency, and partial or no resolution shows that an inhibitor is present. This difference stems from the above mentioned fact that the APTT will be normal in the presence of 50% normal activity³.

Conditions in which APTT is prolonged include inherited disorders, such as haemophilia A and B and other congential absences of intrinsic and common factors. Acquired factor deficiency also occurs, for example with vitamin K deficiency, liver dysfunction, prolonged bleeding or disseminated intravascular coagulation. The most common inhibitors found to prolong APTT are the antithrombins, which inhibit the activity of thrombin on the conversion of fibrinogen to fibrin. Examples include heparin and fibrin degradation products.

Conditions in which APTT is prolonged include inherited disorders, such as haemophilia A and B and other congential absences of intrinsic and common factors. Acquired factor deficiency also occurs, for example with vitamin K deficiency, liver dysfunction, prolonged bleeding or disseminated intravascular coagulation. The most common inhibitors found to prolong APTT are the antithrombins, which inhibit the activity of thrombin on the conversion of fibrinogen to fibrin. Examples include heparin and fibrin degradation products.

===Prothrombin Time===

===Prothrombin Time===

Prothrombin time (PT) gives an assessment of the extrinsic and common pathways by measuring the time necessary to generate fibrin after activation of factor VII³. It is performed by an automated analyser² using citrated plasma^{1, 3}. Blood should therefore be collected into a sodium citrate tube if prothrombin time is to be performed. In basic terms, the test procedure involves adding thromoplastin to the patient's plasma, warming, adding calcium and recording the time taken to clot¹.

Prothrombin time (PT) gives an assessment of the extrinsic and common pathways by measuring the time necessary to generate fibrin after activation of factor VII³. It is performed manually or by an automated analyser² using citrated plasma^{1, 3}. Blood should therefore be collected into a sodium citrate tube if prothrombin time is to be performed. For the manual test, as a quality control measure it is normal to undertake the test in a sample from an unaffected patient to compare the time taken to clot between the two samples - this will account for variables such as variations in the technique of performing the manual test. The test procedure involves adding rabbit brain thromoplastin to the patient's plasma once it has been warmed to 37⁰C and recording the time taken for the sample to clot¹.

A prolonged PT may reflect a factor deficiency or the presence of a circulating inhibitor of coagulation. Repeating the test using a mix of test plasma and "normal" plasma can help differentiate these possibilities: PT returns to normal limits when normal plasma is added to factor-deficient plasma, but no change is seen when this is added to plasma containing inibitors³. PT is more sensitive than APTT for factor deficiencies.  

A prolonged PT may reflect a factor deficiency or the presence of a circulating inhibitor of coagulation. Repeating the test using a mix of test plasma and "normal" plasma can help differentiate these possibilities: PT returns to normal limits when normal plasma is added to factor-deficient plasma, but no change is seen when this is added to plasma containing inibitors³. PT is more sensitive than APTT for factor deficiencies.  

PT is affected by abnormalities or deficiencies in coagulation factors I, II, VII or X, for example in DIC, liver disease, or poisoning with vitamin K antagonists. Inherited defects are possible. PT is also prolonged by the presence of circulating anticoagulants. Inhibitors are often directed at factor X or thrombin and can include fibrin degradation products or heparin³.

PT is affected by abnormalities or deficiencies in coagulation factors I, II, VII or X, for example in DIC, liver disease, endotoxaemia or poisoning with vitamin K antagonists. Inherited defects are possible. PT is also prolonged by the presence of circulating anticoagulants. Inhibitors are often directed at factor X or thrombin and include fibrin degradation products and heparin³. As factor VII has the shortest half-life of all the coagulation factors, if a patient is suffering a coagulation factor deficiency a prolonged PT is seen before a prolonged PTT as this factor is depleted most rapidly.

===Tests for Individual Clotting Factors===

===Tests for Individual Clotting Factors===

Some specialised laboratories offer tests for specific clotting factors. Blood is required to be collected into a sodium citrate tube.

Some specialised laboratories offer tests for specific clotting factors. A sodium citrate sample is required.

===Proteins Induced by Vitamin K Antagonism Test===

===Proteins Induced by Vitamin K Antagonism Test===

A latex agglutination test is available for fibrin degradation products (FDP). To perform the test, anti-FDP antibodies attached to latex particles are added to serial dilutions of test serum. If agglutination is seen at a particular dilution, the test is positive. The most dilute sample that agglutinates gives the overall result of the test. Normal values are between 1/4 and 1/16.

A latex agglutination test is available for fibrin degradation products (FDP). To perform the test, anti-FDP antibodies attached to latex particles are added to serial dilutions of test serum. If agglutination is seen at a particular dilution, the test is positive. The most dilute sample that agglutinates gives the overall result of the test. Normal values are between 1/4 and 1/16.

Although the test is simple to perform, interpretation may be challenging. This is because other small fragments involved in the homeostasis of fibrinogen and fibrin are measured by the test in addition to ''bona fide'' fibrin degradation products. In general, an increase in FDP correspons to increased fibrinolysis. This can be due to a local problem of fibrin generation such as thrombosis, trauma or chronic bleeding, or be related to a systemic process, usually DIC³.

Although the test is simple to perform, interpretation may be challenging. This is because other small fragments involved in the homeostasis of fibrinogen and fibrin are measured by the test in addition to ''bona fide'' fibrin degradation products. In general, an increase in FDP corresponds to increased fibrinolysis. This can be due to a local problem of fibrin generation such as thrombosis, trauma or chronic bleeding, or be related to a systemic process, usually DIC³.

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==Links==

==Links==

#[http://ahdc.vet.cornell.edu/clinpath/modules/coags/pivka.htm Cornell University Clinical Pathology Modules: Tests of Haemostasis - PIVKA]

#[http://ahdc.vet.cornell.edu/clinpath/modules/coags/pivka.htm Cornell University Clinical Pathology Modules: Tests of Haemostasis - PIVKA]

#Howard, M R and (2008) '''Haematology: an illustrated colour text''', ''Elsevier Health Sciences''.

#Howard, M R and (2008) '''Haematology: an illustrated colour text''', ''Elsevier Health Sciences''.

[[Category:Blood Samples and Coagulation Tests]]

[[Category:Blood Samples and Coagulation Tests]]