What is the Chromogenix Coamatic® Protein C measurement principle?

chromogenic protein c assay test kit

Go to Chromogenix Coamatic® Protein C

In the Chromogenix Coamatic® Protein C assay, what substances could interfere with the assay, how will they affect results, and what can be done to overcome the interference?

A low protein C activity is expected in aprotinin treated patients because aprotinin is an inhibitor of activated protein C. Oral anticoagulant therapy interferes with the formation of g-carboxyglutamic acid moiety of the protein C molecules during biosynthesis in the liver, which results in a loss of anticoagulant activity. Non-carboxylated forms of protein C molecules that are inactive in vivo can still be activated by snake venom or thrombin-thrombomodulin and retain amidolytic activity in vitro. Assays using chromogenic substrates will therefore over-estimate the true level of protein C activity in plasma from patients receiving OAC’s. Streptokinase also influences the hydrolysis of S-2366™. Sample blank activities should be determined with plasma from patients with thrombolytic disorder treated with streptokinase, as well as plasma where contact activation is suspected, should be compared to sample blank activities. A high blank activity may indicate contact activation has occurred. S-2366™ is also sensitive to thrombin. This interference can be quenched by the addition of a thrombin inhibitor such as I-2581.

Explain the types of protein C deficiency, and the clinical manifestations.

Hereditary protein C deficiency is inherited as an autosomal dominant trait. Heterozygotes for protein C deficiency have protein C activity or antigen levels of 30-70% normal, whereas homozygotes with a severe defect have levels below 1%. The prevalence of protein C deficiency is 2-5% in patients with thromboembolic disease. Two types of protein C deficiency states are recognized. In type I deficiency, which is the most common type of disorder, the plasma concentration of protein C is reduced both in functional and immunological assays. This reflects a genetic defect causing a reduced biosynthesis of protein C. Type II deficiency is characterized by normal protein C antigen levels, but with decreased functional activity. This type of defect reflects synthesis of abnormal molecules with reduced function. The most common clinical manifestation of symptomatic heterozygous protein C deficiency is deep vein thrombosis (DVT) of the lower extremities. Patients with homozygous protein C deficiency usually suffer from severe and fatal thrombosis in the early stage of life.

Protein C deficiency can also be acquired. Protein C level is influenced by various diseases and drugs such as DIC, DVT, liver disease, sepsis, oral anticoagulant therapy, and surgery.

In contrast, elevated Protein C levels have been reported in such cases as diabetic patients and with the use of anabolic steroids and oral contraceptives. Elevated levels of protein C have no known clinical significance.

What effect does variation of plasma levels of protein C have on the APC ratio?

Variations in plasma levels of protein C have no influence on the APC ratio since a standardized amount of exogenous APC is added.

Describe the protein C pathway and APC resistance. What is the relative risk of venous thrombosis for those who are APC resistant?

Protein C is a vitamin-K-dependent glycoprotein and plasma proenzyme of a serine protease that plays a key role in the down-regulation of blood coagulation. It is activated in vivo by the thrombin-thrombomodulin complex on the surface of intact endothelial cells. Activated protein C (APC) functions as a circulating anticoagulant through proteolytic cleavage and inactivation of the coagulation factors Va and VIIIa. The cleavage occurs at three sites in the heavy chain of each protein. The anticoagulant activity of APC is potentiated by the free form of Protein S (about 60% of PS in plasma is bound to C4bBP, and 40% is in free form) and FV. APC Resistance is actually due to a defect in the protein C pathway, in the factor V molecule as opposed to the activated protein C molecule. APC Resistance is an autosomal dominant hereditary defect mainly due to a point mutation resulting in an amino acid change in the FV gene (Ag506 to Gln mutation, or Factor V Leiden mutation). The mutation destroys one of the three cleavage sites, rendering FVa partially resistant to APC-mediated degradation. APC resistance occurs in 3-5% of the general population, but varies largely in different parts of the world. Up to 90% of APC resistance cases are due to the Factor V:Q506 gene mutation. The relative risk of DVT for carriers of the FV:Q506 mutation is estimated to be 8-fold for heterozygotes and 80-fold for homozygotes.

Protein concentrations in plasma


Weight kDa



Fibrinogen 330 3000 9
Prothrombin 72 150 2
Factor V 330 20 0.05
Factor VII 50 0.5 0.01
Factor VIII 330 0.1 0.0003
Factor IX 56 5 0.09
Factor X 59 8 0.13
Factor XI 160 5 0.03
Factor XII 80 30 0.4
Factor XIII 320 10 0.03
Protein C 62 4 0.06
Protein S 70 10 (free) 0.14
Protein Z 62 2 0.03
Prekallikrein 86 50 0.6
HMW kininogen 120 70 0.6
Fibronectin 450 300 0.7
Plasminogen 92 200 2
t-PA 60 0.005 0.0001
Urokinase 53 0.004 0.0001
Antithrombin 58 145 2.5
Heparin Cofactor II 66 80 1.2
Plasmin Inhibitor 63 60 1
Protein C Inhibitor 57 4 0.07
α2-Macroglobulin 725 2000 3