Low platelets in blood test. Causes and consequences

Author: Sozinova A.V., obstetrician-gynecologist, has been in continuous practice since 2001. January, 2021.

Synonyms: platelets, platelet count, PC, plt.

Platelets are blood cells, and their concentration is determined during a general blood test. On the CBC form, platelets are designated as platelet count or PC. Blood for studying its composition, including counting the number of platelets, is taken from a finger (capillary) or from a vein. The unit of measurement for platelets is the number (N) of cells multiplied by 109 per liter.

Platelets, like other formed elements, are formed in the red bone marrow. Their lifespan in the bloodstream is about 7–12 days. Destruction and breakdown of cells occurs in the spleen and liver tissues.

The main function of platelets is to carry out hemostasis, that is, to stop bleeding. Contact with damaged tissues causes transformation of cells, up to 10 processes are formed in them, and when they spread, the wound is closed with a platelet mass (thrombus). Thus, platelets prevent large amounts of blood from leaking out of damaged soft tissues.

Another equally important function of platelets is to protect the injured area from the penetration of pathogenic microorganisms (they secrete lysozyme and B-lysine).

Platelets also participate in the processes of hemostasis (maintaining the internal environment of the body), nutrition of the capillary endothelium (the inner layer of the walls of blood vessels) and regenerative processes of damaged tissues due to the release of growth factors that stimulate cell division.

A 2021 scientific paper provides evidence showing that in addition to the above functions, platelets also play an important role in the human immune system.

Indications

Prescription of an OAC with a study of platelet concentration is indicated for all patients who visit the clinic, undergo a routine medical examination, or receive a referral for inpatient treatment. Also, platelet determination is prescribed to all patients requiring surgery (emergency or planned). The main indications for platelet testing include:

• suspicion of disturbances in the hemostatic system (bleeding, formation of subcutaneous hematomas);
• suspicion of a malignant process;
• immunity disorders;
• bronchopulmonary pathology;
• diseases of the digestive tract and urinary system (stomach ulcer, glomerulonephritis);
• cardiovascular pathology;
• endocrine disorders (obesity, diabetes).

Symptoms that should alert you

• red, purple bruises on the skin
• frequent nosebleeds, bleeding gums
• prolonged bleeding of even small wounds or cuts
• heavy menstrual bleeding in women

What will the doctor think?

Having familiarized himself with the first results (calculation of platelet indices), the doctor can already imagine different situations regarding the behavior of representatives of the platelet unit in the bloodstream, the state of hemostasis and bone marrow hematopoiesis, taking into account only one indicator - the average platelet volume:

1. MPV is within normal limits. In the circulating blood: cells that have not changed in volume, mature, but not old, full-fledged cells capable of performing their functional tasks at the proper level. The coagulation system and bone marrow are functioning normally.
2. MPV increased. In the bloodstream, along with normal platelets, circulate young blood platelets, increased in size, and giant platelets, which, although they try, but, not having the qualities of full-fledged mature cells, have not acquired their capabilities, and therefore are not able to fully take assume the responsibilities of “healthy” elements of the platelet unit. There is a rush in the bone marrow, blood clotting is impaired.
3. MPV is below normal. In the blood: there are practically no cells of normal size; the platelet link in the bloodstream is represented by small aged platelets that have lost their functions. There are obvious deviations from the norm in hemostasis, bone marrow hematopoiesis is suppressed. Thrombopathy?

Based on studies of the morphological features of blood platelets, as well as on calculations of an automatic analyzer and a histogram, it is possible to discover the relationship between their volume and functional abilities (the adhesive-aggregation function of platelets, due to the content of biologically active substances in their granules).

With “growing up and aging,” the volume of plates decreases, which can be seen in the histogram recording. The presence of the overwhelming majority of young forms in the circulating blood causes the histogram to shift to the right, and the predominant distribution of old blood platelets in the bloodstream shifts to the left.

Preparing for the study

Before taking the OAC, you should stop drinking alcoholic beverages, fatty, spicy, excessively salty and fried foods the day before the procedure. Blood is donated on an empty stomach, the patient is advised to maintain physical and emotional peace (refrain from sudden movements, climbing stairs, avoid stressful situations) for half an hour before the test. Also, platelet testing is not recommended immediately after recovery from a long-term illness, which may distort the results due to weakened immunity.

Detailed instructions for preparing for a general blood test are here.

Prevention

There is no specific prophylaxis for thrombocytopenia. It is recommended to lead a healthy lifestyle, including proper nutrition, normal sleep, not to overload yourself with work, abstain from drinking alcohol and tobacco products, treat infectious diseases in a timely manner and carry out routine vaccinations. Consult a doctor promptly if there is a sudden disturbance in the body’s functioning.

Author: infectious disease doctor. Allergist-immunologist Natalia Nikolaevna Gordienko

Platelet norms

Important! Standards may vary depending on the reagents and equipment used in each particular laboratory. That is why, when interpreting the results, it is necessary to use the standards adopted in the laboratory where the analysis was carried out. You also need to pay attention to the units of measurement.

The list shows the reference values ​​of platelet cells adopted in the Invitro laboratory:

In the Helix laboratory there is a slightly different gradation of values:

It should be noted that the platelet count decreases slightly in women during the menstrual period, but returns to normal after bleeding stops. A slight decrease (up to 150) in platelet concentration during the gestational period is also possible, which is explained by blood dilution due to an increase in BCC (circulating blood volume) and due to insufficient nutrition of the expectant mother.

Important! The interpretation of the results is always carried out comprehensively. It is impossible to make an accurate diagnosis based on only one analysis.

What does the MPV index mean?

When automatically processing blood samples, platelets are counted in the same channel with red blood cells - erythrocytes, so the hematology analyzer can separate particles by signal height in accordance with volume, which allows the device to immediately differentiate them:

• Macroplatelet cells (this group includes elements from 1.8 to 30 femtoliters - in principle, these are the cells that are currently interesting to us);
• Microerythrocytes;
• Fragments of red blood cells - schizocytes;
• Remains of the cytoplasm of white cells - leukocytes or, as it is called, cellular debris.

a – normal platelets b – platelets of different volumes (pronounced anisocytosis) c – huge macroplatelets

Meanwhile, this information alone is very little to characterize the state of platelets. At other times they would have been seen on a stained slide, but now most automated hematology analysis systems provide the various indicators present in the hemogram - mean platelet volume (MPV) and other platelet indices. The average volume of blood platelets is calculated by the automatic hemoanalyzer program using the formula:

MPV = [PCT,% x 1000] /

In addition, the device also includes a histogram for its calculations, which is subsequently studied by the doctor when deciphering the results.

Drugs that affect platelet levels

Long-term use of these drugs may change platelet levels:

• aspirin
• pain relievers such as ibuprofen and naproxen
• antihistamines
• asthma medicine
• sildenafil (Viagra)
• drugs used to prevent blood clots, such as clopidogrel
• antibiotics
• antidepressants and antipsychotic drugs
• Cholesterol-lowering drugs (statins)
• calcium channel blockers (verapamil).

Platelets are reduced (thrombocytopenia)

When the concentration of platelets in the CBC decreases, they speak of the development of thrombocytopenia, which is accompanied by a blood clotting disorder and a tendency to bleed (gums bleed, nosebleeds or intestinal bleeding often occur, menstruation becomes long and heavy). Thrombocytopenia develops in a number of serious diseases due to the loss of elasticity of the vascular wall, their fragility and fragility and the risk of internal bleeding.

Reasons that provoke a decrease in platelet levels include:

• hemolytic-uremic syndrome or Gasser's disease (a combination of hemolytic anemia, thrombocytopenia and acute kidney failure);
• thrombocytopenic purpura or Werlhof's disease (one of the widows of hemorrhagic diathesis);
• allergic thrombocytopenia (taking a number of medications: procainamide, heparin, co-trimoxazole);
• DIC syndrome (second stage);
• severe liver damage (hepatitis, cirrhosis);
• alcoholism;
• malaria;
• enlarged spleen;
• bone marrow diseases, some leukemias;
• megaloblastic anemia;
• pathology of the thyroid gland (hypothyroidism, thyrotoxicosis).

It is important to note that a decrease in platelet concentration (75 – 150) is observed in pregnant women, which is not regarded as a pathology.

How does a blood clot form? Why is a test for induced platelet aggregation prescribed?

Normally, platelets in the blood are in an inactive state; the cells have a discoid, slightly elongated shape, which is why in old textbooks they are called “blood plates.” When bleeding begins, platelets are activated: they acquire a spherical shape and form special outgrowths - pseudopodia. With their help, they can connect with each other (aggregate) and stick to the site of damage to the vascular wall (adhere). These two processes provide the basis for thrombus formation.

To assess the quality of platelet aggregation and find out whether it is reduced or, conversely, does not occur too intensely, an analysis for induced platelet aggregation is prescribed. To do this, they take blood from a vein, add special substances (activation inducers) to it and evaluate the process.

When preparing for the study, it is important to comply with certain conditions - for 3 days, follow a special diet prepared by a doctor, 24 hours before, avoid taking stimulants (coffee, alcohol, nicotine, garlic) and immunostimulant drugs, 8 hours before, stop taking medications and fatty foods.

Low platelet activity occurs in diseases of the hematopoietic system, constant use of antiplatelet drugs, in this case the duration of bleeding increases. Increased aggregation, on the contrary, increases the risk of thrombosis: venous thrombosis, heart attack, stroke. You may ask, why order an induced activation test if the risk of bleeding/thrombosis can be assessed by the total platelet count? Alas. Even with normal numbers, most of the cells may turn out to be “defective”, so we are talking about severe platelet deficiency with their normal concentration in the blood.

Platelets are increased (thrombocytosis)

An increase in platelet count (thrombocytosis) is observed when:

• excessive physical stress
• chronic inflammatory processes (rheumatoid arthritis, tuberculosis, sarcoidosis);
• myeloproliferative diseases (primary erythrosis, chronic myeloid leukemia, myelofibrosis, myelosclerosis);
• some hemolytic anemias;
• hemolysis or severe blood loss;
• carcinoma, lymphoma;
• after removal of the spleen.

Sources:

• Eugenio D. Hottz. Platelets in Immune Response to Virus and Immunopathology of Viral Infections. — Front Med (Lausanne). Apr 2018.
• Data from the independent laboratory Invitro.
• Data from Helix laboratory.
• Steven Kim, MD. Acquired Platelet Function Disorder. — Healthline, Jan 2021
• Douglas B. Cines. Thrombocytopenia in pregnancy. - Blood. 2017 Nov 23; 130(21): 2271–2277
• Danilova L.A., Doctor of Medical Sciences, Prof. Analyzes of human blood, urine and other biological fluids at different age periods, SpetsLit, 2014.