Generality
Platelets are fundamental elements for normal blood coagulation .
Also called thrombocytes, platelets are derived from very large bone marrow cells (called megakaryocytes) and are released into the bloodstream.
What are
Platelets (or thrombocytes) are small fragments of cells, with no nucleus, produced in the bone marrow and released into the bloodstream. These elements have a discoidal shape and a diameter between 2 and 3 µm.
Their function is fundamental for the normal coagulation process, during which the platelets form aggregates that can "plug" a wound immediately after it has formed, before the other coagulation factors intervene.
In detail, when damage occurs to blood vessels or tissues and blood loss begins, platelets intervene in three ways:
- They adhere to the injured area;
- They aggregate with each other, forming a sort of stable cork that remains in place, until the damage is resolved;
- They release chemical factors that further stimulate the aggregation of other platelets.
The average life of platelets is 8-10 days; therefore, the bone marrow must continually produce new elements to replace those that are degraded, consumed and / or lost during bleeding.
An excessive lowering of the level of thrombocytes in the blood increases the risk of incurring bleeding, while an increase in these cells increases, on the contrary, the predisposition to thrombosis (correlated to the formation of platelet aggregates, called thrombi).
Because they measure themselves
The evaluation of platelet parameters is part of the blood count and is indicated for the screening, diagnosis or monitoring of diseases that affect these blood cells, such as haemostatic disorders, bone marrow disorders or other underlying conditions.
The determination of the total platelet count ( PLT or platelet count ) in a blood sample allows a general check of the state of health. At the same time, other platelet parameters can be measured, such as mean volume ( MPV ), distribution amplitude ( PDW ) and blood platelet concentration ( PCT ).
PLT
PLT is a laboratory index that expresses the number of platelets per blood volume.
In an adult, in good health, this value is between 150, 000 and 450, 000 units per microliter of blood. Low PLT values are an index of thrombocytopenia, while high blood concentrations of platelets are an index of thrombocytosis (or platelet).
MPV
MPV is the acronym of "Mean platelet volume", that is "average platelet volume". This parameter indicates how large the platelets are on average: the higher the MPV, the greater the average size of these blood cells.
The average volume (MPV) is a calculation performed by an automated instrument that reflects the size of the platelets present in the patient's blood. When related to the platelet count (PLT), the average volume can give an idea of the efficiency of the blood coagulation mechanisms.
PDW
PDW stands for "Platelet Distribution Width" (amplitude of platelet distribution). This laboratory parameter expresses the degree of variability of platelet size; consequently, a high PDW indicates a large discrepancy between the volumes of these cells, while a low value means that the platelets have uniform dimensions.
In other words, the PDW parameter expresses the degree of uniformity or discrepancy in the size of these cells.
When is the exam prescribed?
The analysis of platelet parameters is indicated by the doctor when the patient experiences prolonged or unexplained bleeding, or other symptoms attributable to a high or low platelet count, such as:
- Easy bruising;
- Prolonged bleeding from a small wound;
- Recurrent epistaxis;
- Abundant and prolonged blood loss during menstruation;
- Gastrointestinal bleeding (which can be detected in a stool sample);
- The appearance of dots or reddish skin spots (petechiae and purpura) and bleeding from mucous membranes.
The examination can also be used to monitor patients with known platelet disorders or those being treated for such alterations, in order to verify their effectiveness.
Associated examinations
The examination of platelet parameters can be carried out together with one or more functional tests and / or other tests for the evaluation of coagulation, such as PT (Prothrombin time) and PTT (Partial Thromboplastin Time).
Sometimes, while monitoring a known disease, a blood smear may be performed to examine the platelets with an optical microscope. This test should be supportive in determining, for example, if the platelets are very few or if they are aggregated during the examination.
Normal values
The platelet count is normally between 150, 000 and 450, 000 units per µl of blood .
Note : the reference interval of the exam can change according to age, sex and instrumentation used in the analysis laboratory. For this reason, it is preferable to consult the ranges listed directly on the report. It should also be remembered that the results of the analyzes must be assessed as a whole by the general practitioner who knows the patient's medical history.
Physiological changes in platelets
- Thrombocyte values lower than normal can be found during pregnancy (especially in the later stages) or in the case of alcohol intake.
- Higher platelet levels are associated with prolonged effort or stay at high altitudes.
Platelets High - Causes
A high blood platelet level ( thrombocytosis ) may depend on:
- Acute and chronic inflammatory states (such as inflammatory bowel disease, rheumatoid arthritis, etc.)
- Anemias (iron lacking or hemolytic);
- Collagen diseases;
- Myeloproliferative syndromes;
- Lung, gastrointestinal, ovarian, breast or lymphoma tumors;
- Surgical removal of the spleen (splenectomy);
- Essential thrombocythemia (or primary thrombocytosis);
- Hemorrhage;
- Leukemia and Hodgkin's disease;
- Reticolosarcomi;
- Chronic iron deficiency;
- Important stress;
- Trauma;
- Excessive physical exercise;
- Some drug therapies (eg oral contraceptives).
Low platelets - Causes
A reduction in platelets ( thrombocytopenia or thrombocytopenia ) may be due to various reasons.
Usually, the main causes include:
- Idiopathic thrombocytopenia (also known as thrombocytopenic immune purpura, is characterized by the production of antibodies directed against platelets);
- Viral, bacterial or fungal infections (eg malaria, leptospirosis, chickenpox, HIV, trypanosomiasis, hepatitis, rubella, mononucleosis, etc.);
- Some drugs: heparin, chemotherapeutic agents, antibiotics (including sulfonamides), barbiturates, H2-receptor antagonists, thiazide diuretics, tolbutamide and para-aminosalicylic acid;
- Leukemia, lymphoma or other tumors that metastasize to the bone marrow;
- Aplastic anemia (in this situation, the production of all blood cells is significantly reduced);
- Long-term bleeding problems (eg chronic blood loss due to stomach ulcers);
- Sepsis, especially that caused by severe bacterial infection caused by Gram-negative;
- Liver cirrhosis (with portal hypertension and increased spleen volume);
- Autoimmune disorders, such as systemic lupus erythematosus;
- Disseminated intravascular coagulation (CID);
- Hemolytic-uremic syndrome;
- Alcohol abuse or exposure to chemicals and toxic substances, such as pesticides, arsenic or benzene;
- Nutritional deficiency (lack of vitamin B12 or folic acid);
- Glomerulonephritis and renal failure;
- Paroxysmal nocturnal hemoglobinuria;
- collagen;
- Preeclampsia;
- Fetal erythroblastosis;
- Von Willebrand disease;
- Valvular aortic disease;
- transfusions;
- Burns.
How to measure them
For the evaluation of platelets, it is sufficient to undergo a complete blood count (blood count). The patient is then taken a blood sample from a vein in the arm, usually in the morning and fasting, at the elbow bend.
Platelet parameters are calculated using an automated haemocytometric analysis tool. In some pathologies, platelets can clump together and appear falsely low in number and / or high size, so a blood smear is required for direct observation of cells under an optical microscope.
Preparation
To undergo blood sampling useful for the examination of platelet parameters, it is necessary to abstain from food and drink for at least 8-10 hours.
Interpretation of Results
Platelets - High Values
The increase in the number of circulating platelets compared to the norm ( thrombocytosis ) can be observed during myeloproliferative syndromes (polycythemia vera and essential thrombocytopenia) and various haematological pathologies (including chronic myeloid leukemia, iron deficiency anemia and myelodysplasia).
Thrombocytosis can also be found in the presence of neoplasms (such as lymphomas, mesotheliomas and carcinomas of the lung, stomach, breast and ovary) and acute inflammatory disorders (eg infections, allergies, Kawasaki disease, rheumatoid arthritis, chronic enteropathies, sarcoidosis, osteomyelitis, osteoporosis and tuberculosis).
Other causes of the increase in platelet values include splenectomy, acute traumatic bleeding, coagulopathy, haemolytic anemias, polyglobulia secondary to renal or cardiac pathology and tissue necrosis from bone fractures, surgery or organ infarcts.
Thrombocytosis can also be found in certain physiopathological conditions, such as hypoxia, intense exercise, post-operative stress, pregnancy and puerperium.
In the presence of thrombocytosis, platelet function is generally normal and does not increase the risk of thrombotic and / or hemorrhagic complications, except in cases where patients do not have a severe arterial disease or are in a state of prolonged immobility.
Platelets - Low Values
A reduction in the number of circulating platelets generally depends on pathological conditions in which:
- The bone marrow fails to produce enough platelets;
- Platelets are consumed or destroyed at splenic level faster than normal.
The thrombocytopenia (or thrombocytopenia) can cause defects in blood coagulation and hemorrhagic manifestations of various types.
A low platelet value can be observed during infectious diseases (eg hepatitis, rubella, mononucleosis and HIV infection), autoimmune diseases (eg systemic lupus erythematosus), aplastic anemia and some neoplastic processes (leukemia and lymphoma).
Other possible causes include: liver cirrhosis (with portal hypertension and increased spleen volume), chronic bleeding problems (eg stomach ulcers), burns and sepsis. The thrombocytopenia can also be the consequence of the action of various toxic substances (eg alcohol or chemical abuse, such as pesticides, arsenic and benzene) and drugs (quinine, chemotherapeutic agents, etc.), which produce dose-dependent myelosuppression or trigger an immune-mediated destruction of platelets.
