Total protein S antigen

Description: 
ELISA method for measuring total protein S. The internal walls of plastic microwells are pre-coated with a monoclonal antibody to TPS. A second antibody to TPS that has been coupled with a peroxidase is added to the microwells along with the plasma whose TPS is to be determined. During a period of incubation, any PS present (free or bound to C4BP) will be sandwiched between the two antibodies and bound to the microwells. Tetramethylbenzidine (TMB) is added as a substrate to the wells and a colour is formed by the action of peroxidise on the TMB. The reaction is stopped using sulphuric acid, and the colour intensity, which is directly proportional to the concentration of TPS present, is measured by a spectrophotometer.

This test is not currently included in the laboratory's UKAS scope of accreditation to ISO15189:2012.
Clinical details: 
The complex orchestration of cellular and molecular participants of haemostasis achieves a crucial yet fine balance of procoagulant and anticoagulant mechanisms. Deficiencies of natural anticoagulant regulators of secondary haemostasis, such as antithrombin, protein C and protein S, and gain of function mutations in genes for FII and FV, are heritable disorders that can shift this balance and increase the risk of venous thromboembolic disease. Protein S (PS) is the vitamin K dependent, non-enzymatic cofactor for the serine protease activated protein C (APC) which functions as a regulator of secondary haemostasis by inactivating FVa & FVIIIa within a forming clot. Zymogen protein C (PC) attaches to vessel endothelium via a specific receptor, endothelial PC receptor (EPCR) and then migrates across the endothelial surface 'in search' of its activator. If a clot is being formed, some of the thrombin leaks onto the endothelial surface and encounters membrane-bound thrombomodulin (TM), whereupon they form a complex that induces a conformational change in thrombin such that it loses procoagulant activity and instead adopts an anticoagulant role by activating PC. The APC/EPCR complex then dissociates from the TM-throbmin complex and the APC is released to migrate onto the surface of an activated platelet. PC & PS are vitamin K dependent and so bind to surface phospholipid and PS orientates the active site of PC above the platelet surface to facilitate inactivation of substrates by cleavage of a small number of peptide bonds. Inactivation of FVIIIa additionally requires zymogen FV to operate synergistically with PS in a cofactor role.Approximately 60% of PS circulates bound to C4b-binding protein and is largely unavailable for functioning as a cofactor for APC. The remainder is termed free protein S (FPS) and is directly available for APC cofactor function. PS also operates as a cofactor for tissue factor pathway inhibitor. Deficiency of PS reduces the effectiveness of haemostasis regulation and tips the balance towards an increased risk of venous thromboembolism.

Protein S (PS) is the vitamin K dependent, non-enzymatic cofactor for the serine protease activated protein C (APC) which functions as a regulator of secondary haemostasis by inactivating FVa & FVIIIa within a forming clot. Zymogen protein C (PC) attaches to vessel endothelium via a specific receptor, endothelial PC receptor (EPCR) and then migrates across the endothelial surface 'in search' of its activator. If a clot is being formed, some of the thrombin leaks onto the endothelial surface and encounters membrane-bound thrombomodulin (TM), whereupon they form a complex that induces a conformational change in thrombin such that it loses procoagulant activity and instead adopts an anticoagulant role by activating PC. The APC/EPCR complex then dissociates from the TM-throbmin complex and the APC is released to migrate onto the surface of an activated platelet. PC & PS are vitamin K dependent and so bind to surface phospholipid and PS orientates the active site of PC above the platelet surface to facilitate inactivation of substrates by cleavage of a small number of peptide bonds. Inactivation of FVIIIa additionally requires zymogen FV to operate synergistically with PS in a cofactor role.

Approximately 60% of PS circulates bound to C4b-binding protein and is largely unavailable for functioning as a cofactor for APC. The remainder is termed free protein S (FPS) and is directly available for APC cofactor function. PS also operates as a cofactor for tissue factor pathway inhibitor. Deficiency of PS reduces the effectiveness of haemostasis regulation and tips the balance towards an increased risk of venous thromboembolism. "
Reference range: 

68.6 - 111.8 iu/dL

Units: 
iu/dL
Sample type and Volume required: 
External requests: Citrated platelet poor plasma 500µL x 1 aliquot. Internal requests: please refer to EPR label

Turnaround time: 
10 - 14 days
Special sample instructions: 

The sample should be analysed or processed & stored within 4 hours of venepuncture. Please ensure sample tubes are filled exactly to the fill-line as underfilling or overfilling creates a dilution error and leads to inaccurate results.

Storage and transport: 
It is advised that citrated plasma is frozen prior to transport and sent to the laboratory on dry ice to maintain sample quality and integrity.
Contacts:
Diagnostic Haemostasis and Thrombosis Department
St Thomas': 020 7188 2797; Guy's: 020 7188 7188 ext. 53860
St Thomas' Hospital
North Wing - 4th and 5th Floors
Westminster Bridge Road
London SE1 7EH

Laboratory opening times
24/7

Guy's Hospital
Southwark Wing - 4th Floor
Great Maze Pond
London SE1 9RT

Outside core hours, contact Duty Haemostasis Biomedical Scientist
For clinical advice or interpretation of results, please contact the laboratory in the first instance.

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Last updated: 09/07/2021