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(Created page with "<section begin="clinical biochemistry" />Several laboratory tests can be used to evaluate the coagulation system. They're used in the evaluation of bleeding disorders. == Summary == {| class="wikitable" !'''Parameter''' !'''Function examined''' !'''Normal range''' !'''Elevated result in''' |- !Prothrombin time |Extrinsic pathway, vitamin K-dependent factors |15 – 20 seconds |Vitamin K deficiency, liver disease |- !INR |Extrinsic pathway, vitamin K-dependent fa...")
 
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<section begin="clinical biochemistry" />Several laboratory tests can be used to evaluate the [[coagulation system]]. They're used in the evaluation of [[bleeding disorders]].
<section begin="clinical biochemistry" /><section begin="physiology" />Several laboratory tests can be used to evaluate the [[coagulation system]]. They're used in the evaluation of [[bleeding disorders]].


== Summary ==
== Summary ==
{| class="wikitable"
{| class="wikitable"
!'''Parameter'''
!'''Parameter'''
!Coagulation factors evaluated
!'''Function examined'''
!'''Function examined'''
!'''Normal range'''
!'''Normal range'''
!'''Elevated result in'''
!'''Elevated result in'''
|-
|-
!Prothrombin time
!Prothrombin time and INR
|Extrinsic pathway, vitamin K-dependent factors
|I (fibrinogen), II (prothrombin), V, VII, or X
|15 – 20 seconds
|Extrinsic pathway, common pathway, vitamin K-dependent factors
|Vitamin K deficiency, liver disease
|15 – 20 seconds (PT), 1.0 (INR)
|Vitamin K deficiency, liver disease, DIC, warfarin therapy, coagulation factor deficiency
|-
|-
!INR
!aPTT
|Extrinsic pathway, vitamin K-dependent factors
|I (fibrinogen), II (prothrombin), V, VIII, IX, X, XI, and XII
|1.0
|Intrinsic pathway, common pathway
|Vitamin K deficiency, liver disease
|25 - 33 seconds
|Liver disease, DIC, unfractionated heparin therapy, coagulation factor deficiency, haemophilia
|-
!Thrombin time
|I (fibrinogen)
|Last step of common pathway
|17 - 21 seconds
|Fibrinogen disorder, thrombin inhibitor therapy
|-
|-
!Clotting time
!Clotting time
|VIII, IX, XI, XII
|Intrinsic pathway
|Intrinsic pathway
|5 – 8 minutes
|5 – 8 minutes
|Vitamin K deficiency, haemophilia
|Vitamin K deficiency, haemophilia, unfractionated heparin therapy, fibrinogen disorders
|-
|-
!Bleeding time
!Bleeding time
|Primary haemostasis
|None
|Primary haemostasis (platelet function, vascular response)
|2 – 4 minutes
|2 – 4 minutes
|Thrombocytopaenia, von Willebrand disease
|Platelet disorder, von Willebrand disease
|}
|}


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The problem with prothrombin time is that the result varies significantly from lab to lab, depending on equipment and substrates used. As such, the prothrombin time is rarely evaluated alone, but the INR is used instead.  
The problem with prothrombin time is that the result varies significantly from lab to lab, depending on equipment and substrates used. As such, the prothrombin time is rarely evaluated alone, but the INR is used instead.  


The '''international normalised ratio''' (INR) is a standardised form of prothrombin time which is normalised so that the result is similar between different laboratory methods and equipments. The prothrombin time is first measured and then normalised by a specific equation and factor. INR is generally used instead of prothrombin time for the same indications.
The '''international normalised ratio''' (INR) is a standardised form of prothrombin time which is normalised so that the result is similar between different laboratory methods and equipments. The prothrombin time is first measured and then normalised by a specific equation and factor. INR is generally used instead of prothrombin time for the same indications.<section end="physiology" />


Indications:
Indications:
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=== Coagulation factor deficiency ===
=== Coagulation factor deficiency ===
Several coagulation factors can be congenitally or acquired deficient. The PT and INR are prolonged in case of deficiency of fibrinogen (factor I) and factors II, V, VII, or X.
Several coagulation factors can be congenitally or acquired deficient. The PT and INR are prolonged in case of deficiency of fibrinogen (factor I) and factors II, V, VII, or X.
 
<section begin="physiology" />
== Activated partial thromboplastin time (aPTT) ==
== Activated partial thromboplastin time (aPTT) ==
The '''activated partial thromboplastin time''' (aPTT) evaluates the intrinsic and common pathways of coagulation. It's measured by taking the time it takes for plasma to clot when exposed to a reagent which contains phospholipids, silica, and a thromboplastic material without tissue factor. This material activates contact factor, initiating the intrinsic pathway.
The '''activated partial thromboplastin time''' (aPTT) evaluates the intrinsic and common pathways of coagulation. It's measured by taking the time it takes for plasma to clot when exposed to a reagent which contains phospholipids, silica, and a thromboplastic material without tissue factor. This material activates contact factor, initiating the intrinsic pathway.


The aPTT varies depending on the specific reagent used and different instruments. There is no normalised form of aPTT (as INR is to PT). As such, the normal range varies from lab to lab and cannot be compared with other labs.
The aPTT varies depending on the specific reagent used and different instruments. There is no normalised form of aPTT (as INR is to PT). As such, the normal range varies from lab to lab and cannot be compared with other labs.
 
<section end="physiology" />
Indications:
Indications:


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* Evaluate for deficiency of coagulation factors I (fibrinogen), II (prothrombin), V, VIII, IX, X, XI, and XII
* Evaluate for deficiency of coagulation factors I (fibrinogen), II (prothrombin), V, VIII, IX, X, XI, and XII
** This includes [[haemophilia]] A, B, and C, the congenital deficiency of factors VIII, IX, and XI, respectively
** This includes [[haemophilia]] A, B, and C, the congenital deficiency of factors VIII, IX, and XI, respectively
 
<section begin="physiology" />
== Thrombin time ==
== Thrombin time ==
The '''thrombin time''' evaluates the function of the common pathway alone, more specifically, the final step where [[fibrinogen]] is converted to fibrin. It's determined by adding thrombin to citrated plasma and measuring the time to clotting. It's mostly used to evaluate for fibrinogen disorders.
The '''thrombin time''' evaluates the function of the common pathway alone, more specifically, the final step where [[fibrinogen]] is converted to fibrin. It's determined by adding thrombin to citrated plasma and measuring the time to clotting. It's mostly used to evaluate for fibrinogen disorders.
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The '''bleeding time''' evaluates the function of the vasoconstriction and platelet plug formation. It’s normally 2 – 4 minutes. It’s determined by puncturing the finger and measuring the time it takes for it to stop bleeding.
The '''bleeding time''' evaluates the function of the vasoconstriction and platelet plug formation. It’s normally 2 – 4 minutes. It’s determined by puncturing the finger and measuring the time it takes for it to stop bleeding.


The bleeding time is neither sensitive nor specific nor standardised nor reproducible and is therefore no longer used clinically. Other coagulation tests are used instead.
The bleeding time is neither sensitive nor specific nor standardised nor reproducible and is therefore no longer used clinically. Other coagulation tests are used instead, such as platelet aggregation test.
 
<section end="physiology" />
[[Category:Physiology]]
[[Category:Physiology]]
[[Category:Laboratory Medicine]]
[[Category:Laboratory Medicine]]