Platelet Function Tests

Introduction

Platelets are small cells present in the blood that are crucial for blood clotting. Blood clotting is the process that helps to stop bleeding after a traumatic injury. There are primarily two types of platelet tests: a platelet count test and a platelet function test. A platelet count test helps to measure the number of platelets in the blood. A lower-than-normal platelet count is called thrombocytopenia. It is called thrombocytosis when the platelet count is higher than normal. Platelet function tests are a group of investigative procedures that utilize specialized machines to measure the platelets’ ability to aggregate and promote clotting in a blood sample.

What Are Platelet Function Tests?

The main goal of platelet function tests is to check the platelets' ability to create blood clots. Platelet function tests comprise of:

• Closure Time - This test helps to measure the time taken by the platelets in a sample of blood in order to plug the tiny tube into a small hole. This function test helps screen different platelet disorders.

• Thromboelastometry - This test helps to determine the strength of a blood clot as it is formed. A strong blood clot is required to stop bleeding.

• Platelet Aggregometry - This is a group of four to eight tests that are used to measure the aggregation of the platelets over several minutes.

• Lumiaggregometry - This test measures the release of the light when certain organic agents are added to a sample of blood. The light is produced from the small platelet granules that may help to show the presence of defects in the platelets.

• Flow Cytometry - Lasers are used in this procedure to identify certain proteins on the surface of the blood platelets. This helps to diagnose inherited blood platelet disorders. It is a specialized test that is only available at a few medical hospitals and clinical laboratories.

• Bleeding Time - This assay helps to measure the time required for blood to stop flowing after small incision cuts are made in the patient’s forearm. It was a very commonly used platelet function test. However, now other platelet function tests are used more commonly due to the advent of newer tests that provide more reliable results.

What Are the Platelet Function Tests Used For?

A platelet function test is most often used to monitor or diagnose certain inherited platelet disorders and bleeding complications in individuals.

Platelet function tests may be used to:

• Help identify certain platelet disorders.

• Check the proper functioning of the blood platelets during complex surgical techniques, such as heart bypass surgery and accidental trauma surgery. These types of medical procedures have a higher risk of bleeding.

• Evaluate patients before any medical surgery if they have a family history of inherited bleeding disorders.

• Monitor patients who are taking anticoagulants (blood thinners). These drugs may be given to reduce clotting in patients who are at an increased risk for heart attacks or brain stroke.

Why Is a Platelet Function Test Needed?

A platelet function test is required if the patient is having the following symptoms of having very few or an excessive number of platelets.

Symptoms of a very few platelet count include:

• Persistent bleeding after a minor injury or trauma.

• Epistaxis (bleeding from the nose).

• Bruising of unexplained cause.

• Petechiae (pinpoint-sized red dots on the surface of the skin).

• Purpura (purplish spots on the skin surface). These may be caused by bleeding under the skin.

• Heavy menstrual cycle or prolonged periods.

Symptoms of an excessive number of blood platelets include:

• Numbness of upper and lower extremities.

• Severe headache.

• Lightheadedness and dizziness.

• Weakness.

• Lethargy.

Platelet function testing is also recommended if the patient is:

• Undergoing a complex surgical procedure.

• Taking blood thinners to reduce blood clotting.

What Happens During a Platelet Function Test?

Most platelet function tests are done on the patient’s blood sample. During the test, a healthcare technician will draw blood from a vein in the arm using a small needle. The patient may feel a little sting when the needle is inserted in or out. This procedure usually takes less than five minutes.

The patient should stop taking certain medicines, such as Aspirin and Ibuprofen, before the platelet function test. The health care professional will tell if any other special instructions are needed to follow before the test.

What Do the Platelet Function Test Results Suggest?

If the platelet function test results are not normal, it may be suggestive of an inherited or acquired platelet blood disorder. Inherited platelet disorders are passed down within the family. The condition is present at birth, but the symptoms may appear when the person becomes older. Acquired platelet disorders are not present at birth. They are usually caused by other disorders, certain drugs, or environmental exposure. Sometimes the etiology is also unknown.

Inherited platelet disorders include:

• Von Willebrand disease is an inherited blood disorder that reduces the synthesis of platelets or causes the platelets to function less effectively. As a result, the blood does not clot properly, which can lead to excessive bleeding.

• Glanzmann's thrombasthenia is a blood disorder that affects the ability of the blood platelets to aggregate together and form a clot.

• Bernard-Soulier syndrome is a disorder that limits the platelet’s ability to aggregate together.

• Storage pool disease is another condition that affects the ability of the blood platelets to release certain organic substances that aid in the clumping of platelets together.

Acquired platelet disorders may occur due to certain chronic diseases, such as:

• Renal failure.

• Different types of leukemia (white blood cell cancer).

• Myelodysplastic syndrome (a disorder of the bone marrow).

Conclusion

Platelet function tests are carried out to help determine the potential cause for excessive bleeding and to identify a platelet function disorder. These tests can also be used to monitor and evaluate the functions of platelets and to monitor the effectiveness of anti-platelet drugs. These tests also help to indirectly analyze the person’s platelet activity. If the tests are functioning normally, they suggest the platelets are functioning well to aid in blood clotting. Patients with bleeding disorders should go for frequent screening of these tests.