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Protein S

Alexey Portnov, medical expert
Last reviewed: 23.04.2024

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The reference values (norm) of the concentration of total protein S in blood plasma are 60-140%, free - 65-144%.

Protein S is a vitamin K-dependent plasma glycoprotein. It circulates in the blood in two forms: free (40%) and associated with the C ₄ complement component (60%). They are in dynamic equilibrium, but only free protein is active. Protein S is a cofactor of protein C in the process of inactivation of Va and VIIIa of clotting factors. The currently available ELISA test systems allow the determination of the concentration of free protein S, which is of paramount importance for clinical practice.

The content of protein S in the blood of men is higher than that of women. Indirect anticoagulants affect it weaker than on protein C, this is due to the fact that protein S is synthesized in endothelial cells of the liver and megakaryocytes. With liver diseases, its level is higher than that of protein C. Since the bulk of protein S is associated with the C ₄ complement component, the amount of free protein S decreases with increasing C ₄ concentration (acute phase of inflammatory diseases or exacerbation of chronic). Reducing the concentration of protein S in the blood is possible with nephrotic syndrome due to its loss.

Classification of protein deficiency S

Type I - insufficiency of the total protein S.
Type II - deficiency of free protein S at normal or borderline content of total protein S.
Type III - dysfunction of protein S with a weakened anticoagulant activity.

Deficiency of protein S leads to the development of venous thrombosis, especially in young people.

Indicators of the anticoagulant system and risk factors for thrombohemorrhagic complications

Investigated indicators	Norm,%	Deviation of the studied indicators,%
ATIII	80-120	<80 - high risk factor for thrombosis > 120 - high risk factor for hemorrhages
Protein C	70-130	<70 - high risk factor for thrombosis
Protein S	60-140	<60 - high risk factor for thrombosis

The main points of application of anticoagulants

Anticoagulants

Phases of hemostasis

Inhibited factors of the coagulating system of blood

ATIII

Protein C

Protein S

Heparin:

Low concentrations;

High concentrations

Indirect anticoagulants

I, II

I, II,

II, I

I, II

Xa, XIIa, IXa

Va, VIIIa

IXa, VIII, Xa, IIa

On all factors and platelet aggregation

Vitamin K-dependent factors - II, VII, IX, X

trusted-source [1], [2], [3], [4], [5], [6]