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Related Concept Videos

Coagulation01:09

Coagulation

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The coagulation phase is a critical part of the body's process to prevent blood loss following injury to blood vessels. It involves chemical reactions that form a clot to seal the injured area. The clotting process begins shortly after injury, within 15-20 seconds for severe damage and 1-2 minutes for minor injuries.
During the coagulation phase, clotting factors, or procoagulants, play a vital role in initiating and progressing the coagulation cascade. This cascade is a series of reactions...
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Coagulation01:06

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Colloidal solids are solid particles suspended in solution. They are usually negatively charged, attracting a compact primary layer of positively charged ions, which attract more counterions to form an electrical double layer. Electrostatic repulsion between the charged double layers prevents the particles from colliding, stabilizing the colloids. These solids are often undesirable because they can contain toxins that are difficult to remove. Coagulation is a technique that helps aggregate and...
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Extrinsic and Intrinsic Pathways of Hemostasis01:20

Extrinsic and Intrinsic Pathways of Hemostasis

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Blood clotting or coagulation involves extrinsic and intrinsic pathways, which ultimately merge into the common pathway, forming a fibrin clot.
The Extrinsic Pathway
The extrinsic pathway of coagulation is typically initiated by tissue damage that exposes blood to tissue factor (TF), a protein released by the damaged tissue cells outside the blood vessels—this interaction with TF triggers biochemical reactions involving specific clotting factors. The key player here is Factor VII, which...
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Introduction to Hemostasis01:05

Introduction to Hemostasis

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Hemostasis is a complex physiological process that prevents excessive bleeding when a blood vessel is injured. It's crucial for maintaining the integrity of the circulatory system, as it ensures that our blood remains fluid while still within the vascular network and yet clots to prevent blood loss upon vessel injury.
The three phases of hemostasis involve many clotting factors present in plasma and several substances released by platelets and injured tissue cells. It is a fast, localized,...
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Anticoagulant Drugs: Low-Molecular-Weight Heparins01:30

Anticoagulant Drugs: Low-Molecular-Weight Heparins

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Hemostasis is a crucial process that prevents excessive blood loss from damaged blood vessels. It involves various mechanisms such as vasoconstriction, platelet adhesion and activation, and fibrin formation. The importance of each mechanism depends on the type of vessel injury. In contrast, thrombosis is the abnormal formation of a blood clot within the blood vessels, leading to potential complications if the clot obstructs blood flow. Thrombosis can be caused by increased coagulability of the...
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Clot Retraction and Fibrinolysis01:16

Clot Retraction and Fibrinolysis

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After a fibrin clot is formed, the next step is clot retraction, a vital process facilitated by platelet contractile proteins, such as actin and myosin. These proteins pull the fibrin strands closer together and condense the clot. This action reduces the size of the clot, creating a smaller, denser structure that effectively seals off the damaged vessel. Clot retraction consolidates the clot and helps with wound healing by bringing the edges of the damaged blood vessel closer together.
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Updated: Apr 27, 2026

A Microfluidic Flow Chamber Model for Platelet Transfusion and Hemostasis Measures Platelet Deposition and Fibrin Formation in Real-time
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A Microfluidic Flow Chamber Model for Platelet Transfusion and Hemostasis Measures Platelet Deposition and Fibrin Formation in Real-time

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Coagulation.

Y L Chee1

  • 1YL Chee Consultant Haematologist Department of Haematology-Oncology NUHS Tower Block Level 7 1E Kent Ridge Road Singapore 119228 e-mail yen_lin_chee@nuhs.edu.sg.

The Journal of the Royal College of Physicians of Edinburgh
|July 5, 2014
PubMed
Summary
This summary is machine-generated.

The prothrombin time (PT) and activated partial thromboplastin time (APTT) tests assess only one part of the hemostatic system. Routine preoperative screening using PT/APTT is generally not recommended without a history of bleeding issues.

Keywords:
Prothrombin timeactivated partial thromboplastin timebleeding historycoagulation screenpreoperative screeningthrombin clotting time

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Area of Science:

  • Hematology
  • Clinical Pathology

Background:

  • The hemostatic system is complex, involving vasculature, platelets, coagulation factors, and fibrinolysis.
  • Current laboratory tests, like PT and APTT, assess only the coagulation protein compartment.
  • No single test can replicate the intricate interactions within the entire hemostatic system.

Purpose of the Study:

  • To provide an overview of the limitations of PT and APTT.
  • To discuss considerations for PT and APTT test requests in clinical contexts.
  • To evaluate the utility of routine preoperative screening with PT/APTT.

Main Methods:

  • Literature review and analysis of current clinical guidelines.
  • Discussion of assay limitations and interpretation of PT/APTT results.
  • Contextual analysis of test indications: anticoagulant monitoring, bleeding symptoms, and preoperative screening.

Main Results:

  • PT and APTT provide limited insight into overall hemostasis.
  • Interpretation requires clinical correlation and awareness of assay constraints.
  • Routine preoperative screening with PT/APTT is often not clinically indicated.

Conclusions:

  • PT and APTT are valuable but limited tools for assessing coagulation.
  • Clinical judgment is crucial for interpreting PT/APTT results.
  • Routine preoperative screening with PT/APTT should be reserved for patients with a bleeding history.