Platelet Count
At a Glance
Why Get Tested?
To diagnose a bleeding disorder or a bone marrow disease
When to Get Tested?
As part of a full blood count (FBC) or to diagnose or monitor a bone marrow or blood disease
Sample Required?
A blood sample taken from a vein in your arm
The Test Sample
What is being tested?
Platelets are tiny fragments of cells made in the bone marrow and circulate in the blood. Because they are very sticky, they are the first components to be activated when there has been an injury to a blood vessel and begin the formation of a "blood clot". The platelet count is a test that determines the number of platelets in your blood.
How is the sample collected for testing?
A blood sample is taken though a needle placed in a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
The Test
How is it used?
Abnormal platelet counts or abnormally shaped platelets are associated with bleeding disorders and other bone marrow diseases, such as leukaemia.
When is it requested?
A platelet count is often requested as a standard part of a full blood count which may be done as part of an annual examination. It is almost always ordered when a patient has unexplained bruises or takes what appears to be an unusually long time to stop bleeding from a small cut or wound.
What does the test result mean?
In an adult, a normal count is about 150,000 to 450,000 platelets per microlitre of blood.
Patients who have a bone marrow disease, such as leukaemia or other cancer in the bone marrow, often experience excessive bleeding, which is generally due to a significantly decreased number of platelets (thrombocytopenia). Low number of platelets may occur in some patients with long-term bleeding problems thus reducing the supply of platelets. Individuals with an autoimmune disorder (such as lupus, where the body’s immune system attacks its own organs) can cause the destruction of platelets. Patients undergoing chemotherapy may also have a decreased platelet count.
More commonly (up to 1% of the population), easy bruising or bleeding may be due to an inherited disease called von Willibrand’s disease. While the platelets may be normal in number, their ability to stick together is impaired. Many cases go undiagnosed due to the mild nature of the disease; however, the more severe form can be devastating.
If platelet levels fall below 20,000 per microlitre, spontaneous bleeding may occur and is considered a risk.
Increased platelet counts (thrombocytosis) may be seen in individuals who show no significant medical problems, while others may have a more significant blood disorder problem called myeloproliferative disorder (abnormal growth of blood cell elements). Some may have a tendency to bleed due to the lack of stickiness of the platelets, yet in others, the platelets retain their stickiness but, because they are increased in number, tend to stick to each other, forming a clump that can get stuck within a blood vessel and cause damage.
Is there anything else I should know?
Living in high altitudes may cause increased platelet levels, as can strenuous exercise.
Decreased levels may be seen in women before menstruation.
Drugs that may cause increased platelet levels include oestrogen and oral contraceptives.
There are many drugs that may cause decreased platelet levels. Check with your doctor.
Common Questions
Ask a Laboratory Scientist
Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
