Platelet tests is a quantitative analysis that aims to determine the level of blood cells responsible for the formation of a blood clot and the prevention of bleeding. This test is performed as part of a general blood test, which allows you to first assess the state of the coagulation system. It is prescribed for routine examinations, with symptoms of delayed blood clotting or increased thrombosis, if bone marrow disease is suspected, as well as before operations, invasive diagnostic procedures. The platelet level is determined in capillary or venous blood. Their calculation is carried out using an automated system, sometimes microscopy of the stained smear is additionally performed. In patients older than 15 years, the norm values range from 180*109 to 320*109 cells/l. The result is prepared in 1 working day.
Platelets are nuclear-free blood cells that ensure the formation of a primary blood clot and help stop bleeding. By their structure, they are biconvex discs, inside of which there are granules containing compounds necessary for blood clotting – fibrinogen, thrombokinase, platelet factor 4, calcium and serotonin. Platelet production occurs in the red bone marrow, the process is regulated by thrombopoietin, a hormone produced in the liver. The precursors of platelets are megakaryocytes – giant multinucleated cells with many processes. Platelets peel off from the surface of megakaryocytes, and, in fact, are fragments of the cytoplasm. Their life span is from 9 to 12 days. After death, the blood plates are absorbed by the inner layer of vessels in the spleen and liver.
The main function of platelets in the body is the formation of a primary thrombus. When a vessel is damaged, substances are formed in the blood that activate platelets. The blood plates flatten and become capable of adhesion – bonding with each other and with the vascular wall. As a result, a blood clot is formed, and the substances released from the granules provide further stages of blood clotting. In addition to this function, platelets nourish and renew the inner surface of blood vessels, absorb hotel types of small bacteria, transport serotonin, Willebrand factor and some other compounds. If their blood level is insufficient, then increased bleeding develops. When the number of platelets exceeds the norm, there is a risk of blood clots.
For platelet tests, blood is taken from capillaries, less often from a vein. During the study, the number of cells in a liter or microliter of the sample is calculated. The procedure is performed using a hematological analyzer, if the values obtained deviate greatly from the norm, then the analysis is supplemented by microscopy of the stained smear, that is, by the “manual” method. Platelet test is most in demand in hematology, surgery and general therapy.
The platelet level is determined during a general blood test during preventive examinations – as part of the medical examination of the population, when entering military service, during pregnancy, etc. The test is also indicated for blood clotting disorders. The basis for its appointment may be complaints of subcutaneous and submucosal hemorrhages of various sizes – petechiae, ecchymosis, bruising, as well as nosebleeds, bleeding gums, blood in urine and feces, copious menstrual bleeding. Such symptoms occur with low and low platelet levels. To determine the cause of the violation, additional clinical, laboratory and instrumental studies are prescribed. The number of platelets decreases in many diseases and conditions: with thrombocytopenic purpura, hepatitis, autoimmune and oncohematological pathologies, disorders in the bone marrow, the use of certain medications.
Blood test for platelets is indicated for increased blood clotting. Symptoms of this pathology include protruding veins, often with “nodules”, heaviness and pain in the legs, headaches, weakness and drowsiness. Increased blood clotting leads to the development of thrombosis, including stroke, myocardial infarction, as well as embolism. Platelet tests is performed during the diagnosis and monitoring of these diseases. In addition, the study is mandatory in preparation for childbirth, for procedures that are accompanied by a risk of bleeding – for operations, for the insertion and removal of a catheter, for puncture and other invasive interventions.
The limitations of the platelet tests include the fact that the result does not indicate the cause of their decrease or increase, it only helps to identify and assess the degree of blood clotting disorders. This study is an economical and affordable diagnostic tool, therefore it is widely used for preventive purposes, as well as in the process of monitoring diseases accompanied by the risk of bleeding or thrombosis. In the diagnosis of pathologies, the determination of platelet levels is supplemented by a biochemical blood test with renal and hepatic samples, a glucose test, a coagulogram, and a bone marrow puncture.
Preparation for analysis
The platelet level can be determined in capillary or venous blood. The sampling procedure is usually performed in the morning, before meals. The minimum period of hunger is 4 hours, but it is recommended to withstand at least 8-10 hours. On the eve of blood donation, you need to stop drinking alcohol, sports training and other heavy physical exertion. A few days before the analysis, it is necessary to consult a doctor about the medications taken, perhaps some of them can affect the level of platelets in the blood and therefore will be temporarily canceled. The last 30 minutes before the procedure should be spent in a calm environment, do not smoke.
To perform a platelet tests, blood is taken from the capillaries of the ring finger or from the ulnar vein. It is stored in a test tube with an anticoagulant and delivered to the laboratory within a few hours. The number of platelets is determined in combination with other indicators of the general blood test using a hematological analyzer. In it, platelets pass through the flow cell, lining up one after another due to hydrodynamic focusing. Electrodes are located on both sides of the flow. When a cell passes between them, an electrical resistance arises. This parameter determines the number of platelets. During smear microscopy, the blood is mixed with the reagent, then applied to the glass and stained. After some time, the dried sample is examined under a microscope – the number of platelets per 1000 red blood cells is calculated. The study is carried out within 1 working day.
For different ages, there are certain indicators of platelet norm:
- children of the first 10 days of life – from 99 *109 to 421* 109 cells / l;
- from 10 days to 1 month – from 150*109 to 400*109 cells/l;
- from 1 to 6 months – from 180*109 to 400*109 cells/l;
- from 6 months to 1 year – from 160*109 to 390*109 cells/l;
- from 1 year to 5 years – from 150*109 to 400*109 cells/l;
- from 5 to 10 years – from 180*109 to 450*109 cells/l;
- from 10 to 15 years – from 150*109 to 450*109 cells/l;
- from 15 years – from 180*109 to 320* 109 cells / l.
The reference values of the platelet test may vary depending on the conditions (reagents, equipment) of a particular laboratory. Therefore, it is necessary to determine the norm according to those indicators that are indicated in the corresponding line in the results form. In addition, an increase or decrease in platelet levels is always interpreted in conjunction with other analysis indicators. Deviation of the result from the norm may be caused by physiological factors, then it does not require treatment. Thus, when smoking, physical exertion and exposure to stress, platelet counts increase.
Increasing the indicator
The cause of thrombocytosis – an increase in platelet levels of more than 450* 109 cells / l – are myeloproliferative diseases, such as true polycythemia, essential thrombocytosis, chronic idiopathic myelofibrosis. With pathologies of this group, the process of hematopoiesis is disrupted, the formation of blood cells increases. An increase in platelet levels against the background of another disease is called secondary thrombocytosis. This condition develops with iron deficiency and hemolytic anemia, chronic inflammatory processes, infections, large blood loss, lymphomas, lung or intestinal cancer, liver cirrhosis, nephritis, as well as after removal of the spleen.
Decrease in the indicator
The cause of thrombocytopenia, that is, a decrease in the level of platelets in the blood, may be insufficient production in the red bone marrow. Such a violation occurs with central thrombocytopenia, leukemia, megaloblastic anemia, alcoholism, autoimmune diseases, parvovirus and helicobacter infection, suppression of the functions of the red bone marrow by drugs, radiation or metastases of malignant tumors. Another reason for the decrease in platelet levels is their increased destruction directly in the bloodstream. This process develops in idiopathic thrombocytopenic purpura, enlarged spleen, DIC syndrome, autoimmune and infectious diseases, heparin-induced thrombocytopenia. The number of platelets decreases with prolonged use of certain medications (for example, valproic acid, penicillin, vancomycin).
The level of platelets in the blood decreases with pathologies such as thrombotic thrombocytopenic purpura, hemolytic-uremic syndrome, DIC syndrome, giant hemangioma. In all these cases, increased production and death of blood plates. A decrease in the level of platelets in the blood due to abnormal redistribution in the body occurs in diseases of the spleen, cirrhosis of the liver, portal hypertension, portal vein thrombosis, hypothermia, after intravenous infusions.
A quantitative platelet tests is performed as part of a general blood test and allows you to first assess the state of the blood clotting system. In clinical practice, it is used quite widely: during preventive examinations, in the detection and monitoring of diseases with a risk of thrombosis, bleeding. If the result deviates from the norm, it is necessary to contact the attending general practitioner, hematologist, surgeon for the diagnosis and appointment of treatment. In order to avoid the influence of physiological factors on the platelet level, it is necessary to properly prepare for the blood sampling procedure: limit physical and emotional stress, refrain from smoking and alcohol consumption.