From the Guidelines
Tissue factor and tissue thromboplastin are indeed the same entity, referring to the protein that initiates the extrinsic pathway of blood coagulation. This is evident from the context in which tissue factor is used in the study of prothrombin time (PT) and international normalized ratio (INR) standardization, as described in the Journal of Thrombosis and Haemostasis 1. The study discusses the role of tissue factor (thromboplastin) reagents in measuring PT, highlighting its crucial role in the coagulation cascade.
Key Points
- Tissue factor, also known as tissue thromboplastin, is a transmembrane glycoprotein that initiates blood coagulation by binding to Factor VII and activating it to Factor VIIa.
- This protein is primarily found in subendothelial tissue and is exposed to blood upon vascular damage, triggering a series of enzymatic reactions leading to thrombin generation and fibrin clot formation.
- The term "tissue thromboplastin" is an older nomenclature, while "tissue factor" is the more modern and commonly used term in medical literature and clinical practice, as seen in the context of PT and INR standardization 1.
- Understanding the equivalence of these terms is essential for interpreting both historical and contemporary medical literature about coagulation.
Clinical Implications
- The standardization of thromboplastin reagents, which are based on tissue factor, is critical for accurate monitoring of vitamin K antagonist treatment, as it directly affects the measurement of PT and calculation of INR 1.
- The use of tissue factor (thromboplastin) reagents from different species (human, bovine, and rabbit) and the development of combined reagents (Owren methods) and plain reagents (Quick methods) underscore the complexity of coagulation testing and the need for precise standardization.
From the Research
Definition and Role of Tissue Factor
- Tissue factor (TF) is a protein that activates the blood clotting system by binding to, and activating, the plasma serine protease, factor VIIa, following vascular injury 2.
- TF is also known as tissue thromboplastin or CD142, and it plays a key role in the initiation of blood coagulation 2, 3.
- The TF/factor VIIa complex is the primary initiator of coagulation in vivo, and tissue factor pathway inhibitor (TFPI) is the physiological inhibitor of this complex 4.
Relationship between Tissue Factor and Tissue Thromboplastin
- Tissue factor and tissue thromboplastin are often used interchangeably, with tissue thromboplastin being an earlier term used to describe the protein 5, 2.
- Tissue thromboplastin was initially used to describe the procoagulant activity of TF, but it is now recognized that TF is the specific protein responsible for this activity 2.
- The terms tissue factor and tissue thromboplastin are often used to describe the same protein, with TF being the more commonly used term in modern scientific literature 6, 3, 4.
Importance of Tissue Factor in Coagulation
- Tissue factor plays a crucial role in hemostasis, and its expression is tightly regulated to prevent excessive coagulation 3.
- Imbalances in TF levels can lead to thrombosis or bleeding, highlighting the importance of measuring TF levels in clinical settings 4.
- The development of sensitive and specific assays for measuring functional TF levels in whole blood and plasma is necessary for patient management in various scenarios 4.