Generality
PLT is a laboratory index that expresses the number of platelets per blood volume . In an adult, in good health, this number is between 150, 000 and 450, 000 units per microlitre of blood.
Low PLT values are an index of thrombocytopenia, while high blood concentrations of platelets are an index of thrombocytosis (or platelet).
What's this
Platelets (or thrombocytes) are small blood cells. Their function is essential for the normal coagulation process.
More in detail, when damage occurs to blood vessels or tissues and bleeding 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.
Platelets derive from very large bone marrow cells (called megakaryocytes) and are released into the bloodstream.
Platelets survive in circulation around 8-10 days and the bone marrow must continually produce new elements to replace those that are degraded, consumed and / or lost during bleeding.
The platelet count is the test that determines the number of platelets in the patient's bloodstream.
PLT and risk of spontaneous bleeding
Platelets play an important and essential role in blood clotting processes. When their number is particularly low, spontaneous bleeding may occur or due to minimal trauma.
Usually, the risk of spontaneous bleeding is very low in the presence of a platelet count of more than 40, 000 platelets / µl, it is frequent but not constant for lower values, and becomes constant and rather serious when PLT falls below 10, 000 platelets / µl.
If spontaneous hemorrhage occurs for values above 40, 000 platelets / µl, on the other hand, other contributing factors must be considered, such as a weakness of the vessel walls, or a defect in platelet function or various coagulation factors.
Why do you measure
The PLT index is measured to determine the number of platelets in a blood sample, as part of a general health check. This evaluation also allows the diagnosis or monitoring of diseases characterized by alterations in the number of platelets, such as haemostasis disorders, bone marrow diseases, hypercoagulability or other problems.
When is the exam prescribed?
The evaluation of PLT is part of the blood count and is indicated by the doctor when the patient experiences prolonged bleeding or other symptoms attributable to a high or low platelet count, such as:
- Easy bruising;
- 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.
Associated examinations
The PLT index test can be performed together with one or more platelet function 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 under a microscope. This should be supportive in determining, for example, if the platelets are very few or if they are aggregated during the test.
Normal values
The platelet count is normally between 150, 000 and 450, 000 units per µl of blood .
This value may vary slightly depending on the phases of the menstrual cycle, decreases in the later stages of pregnancy (gestational thrombocytopenia) and increases in response to inflammatory cytokines (secondary or reactive thrombocytosis).
PLT High - Causes
High PLT and thrombocytosis
INCREASE OF THE PIASTRINICA CONTA PLT MORE THAN 400, 000 units per µl
- PRIMARY THROMBOCYTOSIS: myeloproliferative disorder, characterized by PLT platelet count persistently higher than 600, 000 / mL. HEMORRAGIC MANIFESTATIONS are similar to those observed in patients with platelet diseases: epistaxis, gingivitis, ecchymosis. They can be dangerous after trauma or surgical procedures and be aggravated by the use of acetylsalicylic acid.
- SECONDARY THROMBOCYTOSIS: consequent to acute inflammatory states, chronic, acute hemorrhage, martial deficiency, postoperative states, drugs, physical exercise, etc. Hemorrhagic manifestations are very rare, as well as venous thrombotic episodes.
PLT Low - Causes
Low PLT and thrombocytopenia: possible causes
REDUCTION OF THE PIASTRINICA COUNTER UNDER 150, 000 units per µl.
Due to reduced or defective platelet production:
- Congenital forms, hereditary forms (sex-linked WISKOTT- ALDRICH syndrome, autosomal dominant MAY- HEGGLIN anomaly)
- Acquired forms (aplastic anemia, marrow infiltration during neoplasms, lymphomas, use of substances that alter platelet production, pregnancy, nutritional deficiencies, viral infections, renal insufficiency, paroxysmal nocturnal hemoglobinuria)
Due to reduction of platelets with non-immunological mechanisms:
- Congenital forms (fetal premature erythroblastosis, preeclampsia, infections, KASABACH-MERRIT syndrome, von Willebrand disease)
- Acquired forms (viral, bacterial, mycetic, malaria, trypanosome, burns, CID (disseminated intravascular coagulation), valvular aortic disease, glomerulonephritis, etc.)
- thrombotic thrombocytopenic purpura (ITP)
- uremic-hemolytic syndrome in children and adults
- pregnancy and puerperium
- induced by heparin or other drugs, such as paracetamol, quinidine, digoxin, vancomycin, valium and nitroglycerin
Due to reduction of platelets with immunological mechanism:
- drug-induced
- associated with maternal ITP (idiopathic thrombocytopenic purpura)
- post-transfusion purpura
- Chronic ITP (WERLHOF disease)
- associated with HIV infection
Due to platelet sequestration in some forms of splenomegaly
How to measure it
For the evaluation of the number of platelets per blood volume, it is sufficient to undergo a complete blood count (blood count). A sample of blood from a vein in the arm, usually in the morning and fasting, is then taken from the patient.
Counting can be done automatically by electronic meters or by observation with an optical microscope (blood smear).
Preparation
To undergo blood sampling, it is necessary to abstain from food and drink for at least 8-10 hours.
Interpretation of Results
PLT Low
A low PLT 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 (note: the risk of bleeding is inversely proportional to the platelet count).
A low PLT 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.
A low PLT can 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.) that produce dose-dependent myelosuppression or trigger an immune-mediated destruction of platelets.
PLT High
The increase in the number of circulating platelets compared to the normal rate (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).
A high PLT can also be found in the presence of neoplasms (such as lymphomas, mesotheliomas and carcinomas of the lung, stomach, breast and ovary), acute inflammatory disorders (eg infections, allergies and Kawasaki's disease) and chronic (arthritis rheumatoid, chronic enteropathies, sarcoidosis, osteomyelitis, osteoporosis and tuberculosis).
Other causes include splenectomy and splenic thrombosis, acute trauma hemorrhages, coagulopathies, congenital or acquired hemolytic anemias, polyglobulia secondary to renal or cardiac pathology and tissue necrosis from bone fractures, surgery or organ infarctions.
Thrombocytosis can also be found in certain physiopathological conditions, such as hypoxia, intense exercise, post-operative stress, ovulation, 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.
