Thrombophilia Screen
Description:
To identify in a patient a possible predisposition to thrombosis. The defect is usually inherited but may be acquired in some cases. May be extremely useful to prevent DVT/PE in patients with high risk factors such as long haul flight.
Antithrombin activity
Antithrombin III is a naturally occurring inhibitor. It will inactivate serine proteases and has a special affinity with thrombin and Factor Xa.
In this functional assay plasma is incubated with an excess of Factor Xa in the presence of heparin, which is a co-factor of AT III. The complex AT III:heparin binds rapidly to Xa. The amount of Xa bound is determined by the concentration of AT III in sample. The residual free Factor Xa is measured by its cleavage of a chromogenic substrate. The para-nitroaniline dye released gives a yellow colour which is inversely proportional to AT III concentration.
Protein C activity
Protein C is a vitamin K dependent protein synthesised in the liver. It is activated by thrombin in the presence of calcium ions and phospholipid and the process is accelerated by thrombomodulin.
Activated Protein C Resistance
Activated Protein C is enhanced by a co-factor, Protein S, and regulates the coagulation process by neutralising Factors Va and VIIIa.
Protein C is activated by Protac, a specific enzyme derived from the venom of the Copperhead snake (Agkistrodon c. contortrix). Activated Protein C cleaves the specific chromogenic substrate and the para-nitroaniline dye released is measured at 405 nm.
Activated Protein C Resistance (APCR) is a hereditary defect of the Protein C anticoagulant pathway which results in a pre-disposition to thrombo-embolic disease. Activated Protein C, together with its cofactor, Protein S, is an important down-regulator of thrombin formation by inhibiting the activity of activated Factor V (Va) and Factor VIII (VIIIa) in vivo. The phenomenon can be demonstrated in vitro by an abnormally reduced anti-coagulant response in human plasma upon the addition of human Activated Protein C (APC). Therefore, in the classic test the APTT is performed with and without the addition of APC. The basal APTT will be significantly prolonged by the addition of APC in normal individuals due to the deactivation of Factors Va and VIIIa leading to a reduced rate of thrombin formation. Individuals with APCR have significantly shorter APTTs upon the addition APC compared with normals. The result is expressed as a ratio of clotting time with APC divided by basal clotting time without APC. The APC Ratio will be higher in normal individuals. Inherited resistance to activated protein C, associated with the factor V Leiden mutation G1691A has been shown to be present in 20-50% of individuals with a history of deep vein thrombosis (DVT). G to A transition at position 20210 in the 3’ untranslated region of the prothrombin gene has also been implicated in the pathogenesis of venous thrombosis with an incidence of 5-7% in patients with at least one confirmed episode of DVT.
Heterozygosity for the Prothrombin G20210A variant has been shown to increase the risk of venous thrombosis by up to 3 fold. (Prothrombin G20210A genotype G/A)
Heterozygosity for factor V Leiden mutation is associated with a 5-10 fold increased risk of thrombosis. (Factor V Leiden genotype G/A)
The presence of Homozygous Factor V Leiden (Factor V Leiden genotype A/A) has been shown to increase the risk of venous thrombosis by 50-100 fold.
Antithrombin activity
Antithrombin III is a naturally occurring inhibitor. It will inactivate serine proteases and has a special affinity with thrombin and Factor Xa.
In this functional assay plasma is incubated with an excess of Factor Xa in the presence of heparin, which is a co-factor of AT III. The complex AT III:heparin binds rapidly to Xa. The amount of Xa bound is determined by the concentration of AT III in sample. The residual free Factor Xa is measured by its cleavage of a chromogenic substrate. The para-nitroaniline dye released gives a yellow colour which is inversely proportional to AT III concentration.
Protein C activity
Protein C is a vitamin K dependent protein synthesised in the liver. It is activated by thrombin in the presence of calcium ions and phospholipid and the process is accelerated by thrombomodulin.
Activated Protein C Resistance
Activated Protein C is enhanced by a co-factor, Protein S, and regulates the coagulation process by neutralising Factors Va and VIIIa.
Protein C is activated by Protac, a specific enzyme derived from the venom of the Copperhead snake (Agkistrodon c. contortrix). Activated Protein C cleaves the specific chromogenic substrate and the para-nitroaniline dye released is measured at 405 nm.
Activated Protein C Resistance (APCR) is a hereditary defect of the Protein C anticoagulant pathway which results in a pre-disposition to thrombo-embolic disease. Activated Protein C, together with its cofactor, Protein S, is an important down-regulator of thrombin formation by inhibiting the activity of activated Factor V (Va) and Factor VIII (VIIIa) in vivo. The phenomenon can be demonstrated in vitro by an abnormally reduced anti-coagulant response in human plasma upon the addition of human Activated Protein C (APC). Therefore, in the classic test the APTT is performed with and without the addition of APC. The basal APTT will be significantly prolonged by the addition of APC in normal individuals due to the deactivation of Factors Va and VIIIa leading to a reduced rate of thrombin formation. Individuals with APCR have significantly shorter APTTs upon the addition APC compared with normals. The result is expressed as a ratio of clotting time with APC divided by basal clotting time without APC. The APC Ratio will be higher in normal individuals. Inherited resistance to activated protein C, associated with the factor V Leiden mutation G1691A has been shown to be present in 20-50% of individuals with a history of deep vein thrombosis (DVT). G to A transition at position 20210 in the 3’ untranslated region of the prothrombin gene has also been implicated in the pathogenesis of venous thrombosis with an incidence of 5-7% in patients with at least one confirmed episode of DVT.
Heterozygosity for the Prothrombin G20210A variant has been shown to increase the risk of venous thrombosis by up to 3 fold. (Prothrombin G20210A genotype G/A)
Heterozygosity for factor V Leiden mutation is associated with a 5-10 fold increased risk of thrombosis. (Factor V Leiden genotype G/A)
The presence of Homozygous Factor V Leiden (Factor V Leiden genotype A/A) has been shown to increase the risk of venous thrombosis by 50-100 fold.
Clinical details:
It is now recognised that long-haul air travel increases the risk of DVT, particularly in passengers who have other risk factors for thrombosis (eg pregnancy, recent surgery, hormone treatments, thrombophilia, previous DVT).
For most passengers, common sense measures including in–flight exercise and avoidance of dehydration are sufficient to prevent DVT. In travellers with thrombophilia, the use of compression stockings and/or anticoagulant medications should be considered.
The screen includes Factor V Leiden, Prothrombin Gene Mutation 20210 G/A.
For most passengers, common sense measures including in–flight exercise and avoidance of dehydration are sufficient to prevent DVT. In travellers with thrombophilia, the use of compression stockings and/or anticoagulant medications should be considered.
The screen includes Factor V Leiden, Prothrombin Gene Mutation 20210 G/A.
Reference range:
Normal Factor V Leiden screen: G/G Normal Prothrombin Gene Mutation 20210A screen:G/G
Department:
Location:
Sample type and Volume required:
4.5 mls of EDTA anticoagulated blood (lavender top) and 5mls of non-anticoagulated blood (gold top)
Turnaround time:
Batches of tests run weekly
Storage and transport:
Blood should be stored at 4°C where possible. Send at room temperature by first class post. If possible, please complete the request form attached and send as a hard copy (do not send electronically) with the sample. This will ensure all relevant information is available and will aid us in processing your test.
Cost:
Please contact Business Development for pricing enquiries
Contacts:
Red Cell Centre - Molecular Diagnostics Laboratory
020 3299 1246 / 2265
kch-tr.pnd@nhs.net
c/o Central Specimen Reception
Blood Sciences Laboratory
Ground Floor Bessemer Wing
King’s College Hospital
Denmark Hill
London SE5 9RS
Mon-Fri, 9.00am-5.30pm
Blood Sciences Laboratory
Ground Floor Bessemer Wing
King’s College Hospital
Denmark Hill
London SE5 9RS
Mon-Fri, 9.00am-5.30pm
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Last updated: 29/09/2022
