Protein C Antigen (PCAg)

Coagulation

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Description

Protein C antigen may be used to help fully characterise the deficiency type in subjects with heritable protein C deficiency.

Protein C shares many features with the other vitamin K dependent factors (i.e. II, VII, IX, X and Protein S). Protein C is synthesised in the liver and requires vitamin K to complete the synthesis of the physiologically competent proenzyme. Protein C has a half life of approximately six to ten hours in vivo.

Protein C activity is reduced in vitamin K deficiency and in the presence of oral anticoagulation by vitamin K antagonists such as warfarin. In anticoagulated patients, the Protein C antigen can be compared (by ratio) to antigen levels of two other vitamin K dependent clotting factors (usually factors VII and X) to indicate whether PC deficiency is likely or unlikely. However, guidelines recommend against measuring protein C in these patients because results have reduced power to detect protein C deficiency.

A low ratio of PC antigen/FVII antigen on at least two occasions suggests type 1 protein C deficiency. Family studies may be required to confirm or deny a diagnosis which is made by a consultant Haematologist.

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Indications

Investigation of heritable PC deficiency. To aid detection of type 1 protein C deficiency in subjects who are fully stable on Warfarin and have INR within the therapeutic range.

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Sample Type

Plasma (Citrate Blue) x 1

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Reference Range

Reference range is indicated on the report.

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Turnaround Time

Within 4 weeks

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Testing Frequency

Monthly.

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External Notes

Warfarin reduces PC levels. Rheumatoid factor can cause ‘non-specific binding’ and falsely raise analyte levels in ELISA assays. Protein C antigen is tested in plasma treated to remove the influence of rheumatoid factor. 

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Patient Preparation

No special requirements.

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References

The phenotypic and genetic assessment of protein C deficiency. Cooper PC, Hill M, Maclean RM. Int J Lab Hematol. 2012 Aug;34.
Baglin et al; British Committee for Standards in Haematology. Clinical guidelines for testing for heritable thrombophilia. Br J Haematol. 2010 Apr;149(2):209-220.

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See Also

Protein C Activity
FVII Antigen
FX Antigen
Thrombophilia Screen

Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.