Summary :
Platelets, also called thrombocytes, are small cells found in the blood that play a key role in clotting and stopping bleeding. The platelet count refers to the number of platelets present in a given volume of blood. This article walks you through the importance of platelets, how they are measured, normal values, and the implications of abnormal levels.
◉ Introduction
Platelets, also called "thrombocytes", are small cell fragments produced in the bone marrow and circulating in the blood. When a blood vessel is damaged, platelets quickly adhere to the wall of the damaged vessel to form a plug and stop bleeding.
The platelet count is a test that measures the number of platelets present in a given volume of blood. It is part of a set of parameters evaluated during a complete blood test (CBC: complete blood count).
- When the platelet count is lower than normal (thrombocytopenia), there is an increased risk of bleeding.
- When the blood platelet count is higher than normal (thrombocytosis), it may be associated with an increased risk of blood clots.
Having too many or too few blood platelets or having platelets that do not work as they should can cause various conditions. The platelet count should be interpreted by a healthcare professional taking into account the clinical context.
◉ Definition and function of blood platelets
Platelets are small, colorless disc-shaped cells found in the blood and spleen. They are produced, along with white and red blood cells, in the bone marrow, more precisely from megakaryocytes. They can exist in two forms:
- Inactive (quiescent) form: Under normal conditions, platelets circulate in the blood in an inactive form. They have irregular structures in the shape of a flat disc.
- Active form: Activation of blood platelets occurs in response to chemical signals released by the injured blood vessel or by other already activated platelets. Activated platelets undergo significant morphological (round with protuberances) and functional changes.
Blood platelets control bleeding in our body. If one of your blood vessels is damaged, it sends signals to platelets. The platelets then rush to the site of damage and form a plug (clot) to repair the damage.
◉ Normal and pathological levels of platelets count
The reference platelet count, usually expressed as the number of platelets per microliter (or mm3) of blood, may vary slightly between laboratories and specific populations.
| Platelets per microliter (or mm3) | |
| Normal platelet count | 150,000 to 400,000 |
| High platelet count | Over 450,000 |
|
Low platelet count low Moderate Serious Severe |
Less than 150,000 100,000 to 150,000 50,000 to 100,000 Less than 50,000 Less than 20,000 |
◉ Causes and Symptoms of Platelet Count Disorder
• Low platelet count
A platelet count that is lower than normal is called thrombopenia or thrombocytopenia. This condition can cause:
- Increased bruising.
- Petechiae, Purpura
- Bleeding nose and gums.
- Prolonged bleeding after a cut or other injury.
- Prolonged bleeding with surgery.
- Excessive menstrual bleeding (Menorrhagia).
- Blood in urine, blood in urine.
Potential causes of a low platelet count include:
- Alcohol use disorder.
- Viral infections (hepatitis C, HIV, Mononucleosis, Chickenpox, etc.) or bacteria.
- Autoimmune diseases.
- A cancer that affects the blood, such as leukemia or lymphoma.
- Enlarged spleen.
- Bone marrow infection or injury.
- Exposure to chemicals.
- A side effect of a medication or treatment.
- Infections or dysfunction of the kidneys.
- Gestational thrombocytopenia (affecting pregnant women).
- Cirrhosis, Collagenosis.
- Neonatal purpura, idiopathic thrombocytopenic purpura.
- Polytransfusion.
- Vitamin B12 deficiency.
• High platelet count
A platelet count that is higher than normal is called thrombocytosis or thrombocythemia. This can cause your blood to clot more than necessary and can cause:
- Blood clots that can develop anywhere in the body.
- Confusion or changes in speech
- Upper body discomfort in one or both arms, back, neck, jaw or abdomen
- Migraines
- Shortness of breath and nausea (stomach ache)
- Chest pain
- Weakness
- Pain and swelling in the legs
- Spleen or liver larger than normal
Potential causes of a high platelet count include:
- Mutations or changes in genes (eg JAK2, CALR, MPL) that control bone marrow (essential thrombocythemia).
- Viral or bacterial infection
- Inflammatory disease
- Blood diseases
- Bone marrow abnormalities
Note:
- Some disorders cause abnormal platelet function (Thrombopathies), leading to bleeding problems even with normal platelet counts. Examples: Glanzmann thrombasthenia and Bernard-Soulier syndrome.
- Many people with abnormal blood count and no symptoms. These conditions can be discovered only after routine blood tests.
◉ Platelet count test
The platelet count test is a blood test commonly done to assess the number of platelets present in the blood. It is part of a complete blood count that measures different blood components, including red blood cells, white blood cells, and platelets.
Blood sample collection is usually performed by a lab technician using the following steps:
- Identifies a suitable vein on the inside of the patient's arm, usually near the elbow.
- Place a tourniquet around the upper arm, which is a tight band or cord. This tourniquet helps increase blood flow to the veins, making it easier to draw blood.
- Cleanses the skin surrounding the chosen vein to maintain hygiene.
- Inserts a needle into the vein.
- Collects the required amount of blood into a collection tube.
- Remove the needle and release the tourniquet.
- Apply a small bandage to the puncture site to promote healing and prevent bleeding.
The collected blood sample is then analyzed using a small machine to count platelets (hematology analyzers) and other blood cells. This process usually takes a minute to generate the results.
◉ Additional tests
There are several additional tests that can be used to further assess platelet disorders:
- Blood film (FS): Observing platelets on a blood film can detect abnormalities in platelet morphology, the presence of platelet clumps or giant platelets.
- Mean platelet volume (MPV): This represents the average size of platelets in the blood. It can be used as an indirect indicator of platelet production and destruction in the body.
- The Platelet Distribution Index : This measures the variations in size between platelets, providing information about conditions that affect platelet function and health./li>
- Bleeding time: This measures the time it takes to stop bleeding after a small skin incision.
- Platelet Aggregation Test: Examines the ability of platelets to stick together (aggregate) when exposed to different stimuli.
- Flow Cytometry: This test analyzes platelet changes throughout the process using lasers to activate platelet surfaces.
- Bone Marrow Biopsy: This can be useful in the evaluation of platelet disorders, as it allows direct examination of the production, maturation and distribution of blood cells, including platelets, within the bone marrow.
◉ Conclusion
The platelet count is a common test performed to determine the amount of platelets in the blood. Platelets play a crucial role in blood clotting, helping to prevent excessive bleeding.
A decrease in the number of platelets can indicate the presence of specific infections or cancers. Conversely, a high platelet count can put you at risk for harmful blood clots and potential stroke. Therefore, the platelet count is considered an essential laboratory test investigation.