Coagulation involves the action of cells and coagulation (clotting) factors. The cells are platelets, and the coagulation factors are proteins. These proteins are present in the blood plasma and on the surfaces of certain vascular, or blood vessel, cells.
If a person's blood clots too much, they may develop deep vein thrombosis (DVT) and other problems. If it does not clot enough, a person may have hemophilia. In this case, bleeding happens too easily.
How coagulation happens
Nosebleeds can occur easily when a person has hemophilia.
Hemostasis is the process that stops bleeding and prevents damaged blood vessels from losing too much blood.
Coagulation is an essential part of hemostasis. In hemostasis, platelets and a protein called fibrin work together to plug a damaged blood vessel wall. This stops the bleeding and gives the body the chance to repair the damage.
When damage occurs in the endothelium, which is the lining of a blood vessel, platelets immediately form a plug at the site of the injury. At the same time, proteins in the blood plasma respond to form fibrin strands.
In a complex chemical reaction, these strands form and reinforce the platelet plug.
As the platelets gather at the site of an injury to plug, or block it, the coagulation factors act in a series of chemical reactions to strengthen the plug and allow healing to begin.
What is a platelet?
A platelet is a disc-shaped element in the blood that plays a role in blood clotting. During normal clotting, platelets clump together.
What is fibrin?
Fibrin is an insoluble protein that plays a role in blood clotting.
Fibrin collects around the wound in a mesh-like structure that strengthens the platelet plug.
As this mesh dries and hardens, or coagulates, the bleeding stops and the wound then heals.
Where does fibrin come from?
Fibrin develops in the blood from a soluble protein, fibrinogen.
When platelets come into contact with damaged tissue, a series of chemical processes take place that causes a protein called thrombin to convert fibrinogen into fibrin.
Coagulation factors are proteins. The liver produces most of them.
Scientists originally numbered these factors according to the order in which they discovered them, using Roman numerals from I to XIII. When a person has a specific clotting condition, they will lack a particular coagulation factor.
For example, a person with hemophilia will lack:
Factor VIII, or antihemophilic factor A, if they have hemophilia A
Factor IX, or plasma thromboplastin component, if they have hemophilia B, also known as Christmas disease
When a wound damages the wall of a blood vessel wall, it sets off a complex set of chemical reactions involving these coagulation factors.
The process is like a cascade of chemical reactions, as it happens step by step.
The final step is when fibrinogen, also known as Factor I, changes into fibrin, which forms the mesh to plug the wound and stop the bleeding.
Clotting and hemophilia
If clotting does not happen as it should, a person has hemophilia. Hemophilia occurs when a person does not have the full number of clotting factors. This usually occurs when a person inherits a gene that causes them to produce lower levels of clotting factors.
There are two main types of hemophilia — A and B.
People with hemophilia A lack clotting factor VIII, and people with hemophilia B lack clotting factor IX.
According to the National Heart, Lung, and Blood Institute (NHLBI), the severity of a person's hemophilia depends on the amount of clotting factor VII or IX they have in their blood:
- Mild hemophilia: The person will have 5 to 40 percent of the normal clotting factor level.
- Moderate hemophilia: They will have 1 to 5 percent of the normal clotting factor
- Severe hemophilia: They will have less than 1 percent of normal levels
Symptoms and complications
When a person has hemophilia, they may bruise more easily and more severely than other people.
Symptoms of hemophilia include wounds that do not heal and easy bruising.
There is a high risk of complications, some of which can be life-threatening.
Symptoms and complications include:
- bleeding following a superficial injury, even if it is small
- nosebleeds for no apparent reason
- bleeding from the mouth
- spontaneous bruising
- swelling and pain in the joints due to internal bleeding
- bleeding in the brain following a minor blow to the head, leading to headaches, vomiting, confusion, weakness, and possibly seizures
- other organ and tissue damage
- severe loss of blood, leading to hypovolemic shock
- in females, prolonged or heavy menstrual bleeding
Both type A and type B can be mild, moderate, or severe, depending on how low a person's clotting factors are.
Hemophilia usually affects males, but, very rarely, females can have it. Every year, around 1 in 5,000 males are born with the condition, according to the NHLBI. Rarely, it can affect females, according to the Centers for Disease Control and Prevention (CDC).
Living with hemophilia
A person with hemophilia should not use aspirin or certain other drugs. It is important to speak to a doctor before using any new medication.
A person with hemophilia will need to take some precautions to prevent injury and bleeding.
This may include:
- choosing activities and sports with care
- not using medications, such as aspirin, which reduce clotting
- ensuring that all health workers, school teachers, and others know that they have hemophilia
It is essential to follow all medical advice and to attend all appointments the doctor recommends.
Some people may choose to wear some form of medical identification so that others will know what type of action to take and to avoid in case of an emergency.
In 2018, scientists from the Salk Institute announced that they had found a way to provide a "one-shot" therapy for people with hemophilia B, using stem-cell technology.
Mice that received the injection continued to produce the necessary clotting factors nearly a year after having the shot.
In time, this may offer a new type of therapy that will further reduce the risks that people with hemophilia face.
In the past, hemophilia was a life-threatening condition, but the outlook has improved, according to the Genetic and Rare Diseases (GARD) Information Center of the United States National Institutes of Health.
There is not yet a cure for hemophilia, and the outlook depends on the severity of the condition.
With current medical treatment options, however, many people with low levels of clotting factor can live a normal or near-normal lifespan and enjoy a good quality of life.