2. Coagulation Inhibitor Potential [CIP] Assay
Introduction
The Overall Haemostatic Potential [OHP] assay is a global assay of Fibrin generation and Fibrinolysis and which has been evaluated in a number of clinical situations.
Principles & Methodology
The Test involves the generation of a Fibrin Time Curve in which the generation of Fibrin and its subsequent lysis is measured by changes in absorbance at 405nm.
1a. Normal or Test plasma is diluted with a Buffer containing CaCl2, Thrombin [IIa] and t-PA [tissue Plasminogen Activator. The absorbance at 405nm is measured every minute from Time = 0 to Time = 30 minutes. The Fibrinogen in the sample is converted to Fibrin and the added t-PA converts the Plasminogen in the sample to Plasmin and which digests the Fibrin into soluble fibrin fragments.
1b. A 'Blank' is created by diluting Normal or Test plasma with a Buffer that contains no CaCl2, Thrombin [IIa] or t-PA.
2. The Area under the curve is determined by adding together the Absorbance values recorded during the 30 minutes of the test - termed the ABS-sum and then deducting the background absorbance, which corresponds to the initial optical density of the plasma sample before initiation of clotting. The ABS-sum is calculated from the formula:
..where ABS-sum [X] is a mean summation of ABS values obtained from duplicate samples of an unknown plasma sample and ABS-sum [N] is a mean summation of ABS values obtained from duplicate samples of a known pooled plasma sample run in parallel.
When the Fibrin curve is analysed, each ABS value on the graph equates to a specific amount of Fibrin generated at a specific time point.
The Overall Fibrinolysis Potential [OFP] can be calculated from:
.. and represents the data derived from two fibrin aggregation curves - the OHP assay containing t-PA and the OCP that does not contain t-PA.
The Coagulation Inhibitor Potential (CIP) assay is a further development of the Overall Haemostatic Potential [OHP] assay in which a Pentasaccharide is added to the plasma sample to activate Antithrombin and so increase the sensitivity of the assay to functional abnormalities/deficiencies of Antithrombin and in addition Protac is included which activates Protein C to activated Protein C [APC]. In addition omitting t-PA allows more rapid testing recognising that abnormalities of Fibrinolysis are a rare cause of an inherited thrombophilia.