What is a blood clot?
A blood clot occurs when the blood, which is normally in liquid form, becomes solid or partially solid, forming a jelly-like substance called a thrombus. The thrombus is composed of platelets, which are blood clotting cells, and fibrin, which is a protein that forms long fibers that helps fortify the collection of platelets. A blood clot usually forms as a result of an injury, such as a cut on your finger. The platelets and fibrin work to solidify the blood at the site of injury, so you do not hemorrhage and lose excessive amounts of blood.
Sometimes, a thrombus forms where it is not supposed to, in arteries or veins. A thrombus in a leg vein is called a deep vein thrombus, and can cause pain and swelling. A clot in the lung, called a pulmonary embolus, can cause severe shortness of breath and can be deadly. A clot in the heart artery can cause a heart attack; a clot in a brain artery can lead to a stroke.
How do doctors test for blood clotting?
The blood clotting process, or coagulation cascade, is a complex sequence of events in which the body attempts to limit blood loss following injury to a blood vessel. This process involves 13 clotting factors, or proteins, denoted by Roman numerals I-XIII, that each play a role in forming a clot at the site of injury to allow healing of the blood vessel.
When injury occurs, the vessel constricts, or tightens up, to limit the blood loss at the injury site. Then, clotting cells called platelets are dispatched to the injury site to form a plug; this process is called primary hemostasis. The protein von Willebrand factor helps the platelets stick together to form this plug. Secondary hemostasis occurs when a fibrin clot is formed, which is a mesh that keeps the platelet plug stable while the vessel heals. The fibrin clot is formed during a cycle of activation of the clotting factors from their inactivated forms.
What blood test is done for clotting?
A number of blood tests can be used to evaluate for clotting disorders. These include the complete blood count (CBC), PTT, PT, and INR.
The complete blood count shows the number of white and red blood cells, as well as the number of platelets, which are the blood clotting cells. Too many platelets make the blood more prone to clotting; too few platelets make the blood less likely to clot properly.
What is normal PTT?
The PTT test, also called aPTT, or activated partial thromboplastin time, measures how long it takes the blood to clot. The normal PTT value is 30-50 seconds, depending on the specific laboratory drawing your blood.
The PTT test may be ordered by your physician to assess why you might be having easy bleeding or bruising. It does not diagnose a specific medical condition, but helps to determine further tests that might need to be done to arrive at a diagnosis of your condition.
Additionally, hospitalized patients that are given an intravenous blood thinner called heparin have the PTT level checked frequently to ensure that the blood is kept at the optimal level that is neither too thick nor too thin to help treat their medical condition.
What does it mean if PTT is high?
If the PTT is high, the bleeding time is prolonged, which indicates a deficiency or defect of clotting proteins, including factors VIII, IX, XI, or XII. This means that your blood will take longer than normal to form a clot. This test can commonly help diagnose conditions including hemophilia, von Willebrand disease, liver disease, and vitamin K deficiency, and certain autoimmune diseases.
Further testing and evaluation will usually be considered by the physician if the PTT is high, depending on the patient’s specific symptoms and condition.
What does INR mean medically?
The INR stands for international normalized ratio. This is a number that measures how quickly or how slowly the blood clots. The normal INR value is up to 1.1. If your INR is above 1.1, it means your blood takes longer than normal to clot. The normal clotting time for blood is 10-13 seconds. Conditions that can make blood clot more slowly include liver disorders, inadequate amounts of clotting proteins, vitamin K deficiency, or ingestion of blood thinners such as warfarin.
If your INR level is lower than 1.1, it means that your blood clots faster than normal. This can be caused by ingestion of supplements containing vitamin K, eating foods with high vitamin K content, such as broccoli, or use of estrogen as found in birth control pills or hormone replacement medication, among other causes.
If you have a heart condition called atrial fibrillation, or have a mechanical heart valve replacement, you may be prescribed a strong blood thinner called warfarin or Coumadin to take daily. In this case, you will need to have your blood INR level checked on a regular basis, usually every 2-4 weeks, as this medication level can fluctuate in your body and make your blood thicker or thinner depending on your ingestion of foods with high vitamin K levels and other medications you may be taking. The INR level is monitored by your physician.
