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Coagulation Tests

Coagulation Tests

Clotting is what prevents excessive bleeding when you cut yourself. However, the blood moving through your vessels shouldn’t clot. If such clots form, they can travel through your bloodstream to your heart, lungs, or brain, causing a heart attack, stroke, or even death.

Coagulation tests measure your blood’s ability to clot, as well as how long it takes. Testing can help your doctor assess your risk of excessive bleeding or developing clots (thrombosis) somewhere in your blood vessels.

Coagulation tests are usually given in the same manner as most blood tests. Side effects and risks are minimal. A blood sample is sent to a laboratory for testing and analysis.

Purpose of a Coagulation Test

Clotting disorders can cause a dangerous amount of bleeding or clotting. If your doctor suspects you have a clotting disorder, they may recommend one or more coagulation tests. These tests measure various proteins and how they function.

Conditions that can cause coagulation problems include:

  • liver disease
  • thrombophilia, which is excessive clotting
  • hemophilia, which is an inability to clot normally

Coagulation tests are also useful in monitoring people who take medications that affect clotting ability.

Coagulation tests are sometimes recommended before surgery.

Types of Coagulation Tests

There are many types of coagulation tests. Several of them are explained in the sections below.

Complete Blood Count (CBC)

Your doctor may order a complete blood count (CBC) as part of your routine physical. It can alert your doctor if you have a coagulation problem.

Factor V Assay

This test measures Factor V, a substance involved in clotting. An abnormally low level may be indicative of liver disease, primary fibrinolysis (a breakdown of clots), or disseminated intravascular coagulation (DIC).

Fibrinogen Level

Fibrinogen is a protein made by your liver. This test measures how much fibrinogen is in your blood. Abnormal results may be a sign of excessive bleeding or hemorrhage, fibrinolysis, or placental abruption, which is a separation of the placenta from the uterine wall.

Other names for this test include factor I and hypo-fibrinogenemia test.

Prothrombin Time (PT or PT-INR)

Prothrombin is another protein produced in your liver. The prothrombin time (PT) test measures how well and how long it takes your blood to clot. It normally takes about 25 to 30 seconds. It may take longer if you take blood thinners. Other reasons for abnormal results include hemophilia, liver disease, and malabsorption. It’s also useful in monitoring those who take medications that affect clotting, such as warfarin.

Results are given in the number of seconds it takes to clot. Sometimes the PT test uses a calculation called the international normalized ratio (INR) to compare results of different laboratories.

The PT test is usually ordered with another clotting test called an activated partial thromboplastin time (aPTT). Another version called the model for end stage liver disease (MELD) is used to assess people who need a liver transplant.

Platelet Count

Platelets are cells in the blood that help your blood clot. You may have an abnormally low number if you’re on chemotherapy, take certain medications, or have had a massive blood transfusion. Other causes of a low platelet count are celiac disease, vitamin K deficiency, and leukemia.

An abnormally high number of platelets may be caused by anemia, primary thrombocythemia, or chronic myelogenous leukemia.

Thrombin Time

Thrombin time measures how well fibrinogen is working. Abnormal results may be due to inherited fibrinogen disorders, liver disease, some cancers, and medications that affect clotting.

Bleeding Time

This test analyzes how quickly small blood vessels in your skin close up and stop bleeding. It’s performed differently than the other blood tests.

A blood pressure cuff will be placed on your upper arm and inflated. Your healthcare provider will make a couple of tiny cuts on your lower arm. The cuts are not deep and generally feel like a scratch.

The cuff is then deflated. Blotting paper is briefly placed on the cuts every 30 seconds until bleeding stops.

Bleeding usually lasts between one to nine minutes. The test is considered safe and carries few side effects or risks.

How Coagulation Tests Are Performed

Coagulation tests are conducted the same way as most blood tests. You may be required to discontinue taking certain medications prior to the test. No other preparation is necessary.

Your healthcare provider will sterilize a spot on the back of your hand or inside your elbow. A needle will be inserted into a vein. Most people feel a minor stick.

Blood will be drawn and collected. A small bandage may be placed on the puncture site.

The side effects of a coagulation test are generally minor. You may have slight soreness or bruises at the site. The risks include lightheadedness, pain, and infection.

If you have experienced excessive bleeding, the procedure will be carefully monitored.

The sample will be sent to a laboratory for testing and analysis.


Results from blood tests are sent from the laboratory to your doctor. Values can vary from one laboratory to another, so ask your doctor to explain the results. If you’re diagnosed with a clotting disorder, treatment will depend on the specific diagnosis.

Content licensed from:

Written by: Ann Pietrangelo
Published on: Oct 27, 2015on: May 05, 2017

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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