General (clinical) blood test: interpretation and norm

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

When is a general blood test prescribed?

Donating blood for a general analysis is a familiar procedure to everyone, used both for primary diagnosis and for preventive purposes. Infections, inflammatory reactions or any other pathologies affect the concentration of certain elements in the biomaterial. Changes in each individual or several indicators are very specific and characteristic of a different group of diseases.

A clinical examination is necessarily included in a routine preventive examination and precedes any vaccination. The donation of biological material is also prescribed before the start of drug treatment for a number of diseases, since some drugs affect the composition and, therefore, the properties of blood. For example, the use of anticoagulants is contraindicated when platelet concentrations are low due to the risk of internal bleeding.

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.

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.

General (clinical) blood test: interpretation and norm

A complete blood count provides essential information about the types and numbers of blood cells, especially red blood cells, white blood cells and platelets. Using a general blood test, the treating doctor can detect the nature of symptoms such as weakness, fatigue, and bruising. A complete blood count is used to diagnose anemia, infection and many other disorders.

A general (clinical) blood test includes the following indicators:

• Absolute white blood cell count ( WBC ). White blood cells protect the body from infection. If an infection develops, these cells attack and destroy bacteria, viruses, or other pathogenic organisms. White blood cells are larger in size than red blood cells, but their number is less. When a person gets sick, the number of white blood cells increases very quickly. Sometimes white blood cell counts are used to detect infection or to evaluate the effectiveness of cancer treatment.
• Determination of the ratio of different types of white blood cells (leukogram). The main types of leukocytes are neutrophils, lymphocytes, monocytes, eosinophils and basophils. Counting immature neutrophils, also called band neutrophils, is part of this test. The number of each cell type can provide important information about the health of the immune system. Too high or too low the number of one type of cell may indicate an infection, an allergy or toxic reaction to a drug or chemical, or various diseases such as leukemia.
• Absolute red blood cell count ( RBC ). Red blood cells carry oxygen from the lungs to the rest of the body. They also carry carbon dioxide back to the lungs for exhalation. When the level of red blood cells is low (anemia), the body does not receive enough oxygen. When levels are high (polycythemia), there is a risk of red blood cell clots that can block tiny blood vessels (capillaries), also making it difficult to carry oxygen.
• Hematocrit ( HCT , precipitated red blood cell volume, PCV ). This test measures the volume of blood per red blood cells. For example, a hematocrit value of 38 means that 38% of the blood is red blood cells. Hematocrit and hemoglobin are the two main tests for detecting anemia or polycythemia.
• Hemoglobin ( Hgb ). Hemoglobin molecules are found in red blood cells; they carry oxygen and give the blood its red color. A hemoglobin test measures the level of hemoglobin in the blood and shows how the body copes with transporting oxygen.
• Erythrocyte index. There are three red blood cell indices: mean erythrocyte volume (MCV), mean erythrocyte hemoglobin content (MCH) and mean erythrocyte hemoglobin concentration (MCHC). All of them are calculated using special equipment, and the numbers are derived from other indicators of a general blood test. MCV reflects the size of red blood cells, MCH is the average hemoglobin content in an individual red blood cell, MCHC is the hemoglobin concentration in an individual red blood cell. These indices are used in diagnosing various types of anemia. The red blood cell distribution width (RDW) index is also calculated, which reflects the difference in size and shape between cells.
• Absolute platelet count. Platelets are the smallest type of blood cell. They play an important role in the blood clotting process. If bleeding occurs, the platelets are activated and bind together, forming a plug that prevents bleeding. If the number of red blood cells is insufficient, there is a risk of uncontrolled bleeding. If there is an excess amount, there is a risk of thrombus formation in a blood vessel. In addition, platelets can be involved in the formation of sclerotic plaques on artery walls (atherosclerosis).
• Mean platelet volume ( MPV ). This indicator reflects the average value of the measured platelet volume. MPV is used in conjunction with platelet count to diagnose certain diseases. If the platelet count is normal, the MPV may be low or high.

Your doctor may also order a blood smear microscopy at the same time as your complete blood count, but this is not part of your routine blood test. For this test, a drop of blood is placed on a plate and diluted with dye. The plate is examined under a microscope, noting the number, size and shape of red blood cells, white blood cells and platelets. Differences in the shape or size of blood cells can indicate various diseases, such as leukemia, malaria or sickle cell disease.

A clinical blood test is carried out for the following purposes:

• Finding the cause of symptoms such as fatigue, weakness, fever, bruising, or weight loss
• Diagnosis of anemia
• Establishing the amount of blood lost during bleeding
• Diagnosis of polycythemia
• Diagnosis of infections
• Diagnosis of blood diseases, such as leukemia
• Monitoring the body's response to drug treatment and radiation therapy.
• Monitoring the blood cell response to abnormal bleeding.
• Screening of indicators before surgery.
• Tracking high or low levels is used to detect various diseases, such as high eosinophil levels that may indicate allergies or asthma.

A complete blood count is performed as part of a routine medical examination. A complete blood count provides valuable information about the overall condition of the body and health.

Preparing for the examination

No special preparation required.

How is the examination carried out?

• The shoulder is tightened with an elastic tourniquet to stop the blood flow. The veins under the tourniquet become larger, making it easier to insert the needle.
• The puncture site is cleaned with alcohol.
• The needle is inserted into the vein. Sometimes more than one injection is required.
• A blood collection tube is attached to the needle.
• When enough blood has been collected, the tourniquet is removed.
• After the needle is removed, a cotton swab is applied to the injection site.
• The area should be pressed and a bandage applied.

If a baby's blood is being tested, a heel prick is done instead of drawing blood from a vein.

Feelings during the procedure

A blood sample is taken from a vein in the arm. The forearm is wrapped with an elastic band, so there may be a feeling of tightness. You may not feel any pain from the needle, but sometimes there will be a slight burning sensation or pain.

Complications

When taking blood from a vein, the chance of complications occurring is very small.

• There may be a slight bruise. By pressing the tampon to the puncture site for a few minutes, you can reduce the chance of its occurrence.
• In rare cases, the vein may become swollen, this is called phlebitis. The problem can be treated with several warm compresses.
• Continuous bleeding may occur in patients with blood disorders. Taking medications such as aspirin, warfarin (such as Coumadin), and other blood thinners increases the chance of bleeding. Tell your doctor before taking a sample if you have problems with blood clotting or are taking blood-thinning medications.

results

A complete blood count provides important information about the types of blood cells - red blood cells, white blood cells, platelets - and their numbers. A complete blood count helps determine the cause of various symptoms such as weakness, nausea, bruising and is used in the diagnosis of various diseases - anemia, infections and many others.

Normal results

IMPORTANT! The normal values, or range of normal values, given here are average values. These vary depending on the laboratory, so where you are being tested will have different readings. The laboratory report should contain information about the reference range used. In addition, overall health and other factors are taken into account when analyzing the results. Therefore, a value that does not fit into the range presented here may be normal for you personally.

The normal range depends on your age, gender, type of blood sample, and how high above sea level the area where you live is. The doctor can use all the indicators of the general blood test when checking the condition of the body. For example, the number of red blood cells, hemoglobin, hematocrit are the main indicators in diagnosing anemia, but erythrocyte indices and smear microscopy also help detect this disease and can show the possibility of its occurrence.

To assess the number and size of leukocytes, the doctor takes into account the results of counting the number of cells and the ratio of their types. To see if there are too many or few cells of a certain type, the doctor compares their number and percentage. There is a norm for each type of leukocyte.

Indicators may change during pregnancy. During each trimester, your doctor should report changes in your normal range.

Typically, a normal hemoglobin level is one third of the hematocrit level.

High performance

Absolute red blood cell count (RBC)

• Conditions and habits that cause high red blood cell counts include smoking, exposure to carbon monoxide, long-term lung disease, kidney disease, some cancers and heart disease, alcoholism, liver disease, a rare bone marrow disease (polycythemia vera), or rare problems related to with hemoglobin, which are associated with the transfer of oxygen.
• Diseases related to the water component of the body can also cause high red blood cell counts. These include dehydration, diarrhea, vomiting, increased sweating, and taking diuretics. Lack of fluid in the body causes red blood cell counts to appear high. This is sometimes called pseudopolycythemia.

Absolute white blood cell count (WBC)

• Causes of high white blood cell counts include infection, inflammation, tissue damage (for example, due to a heart attack), kidney failure, lupus, tuberculosis, rheumatoid arthritis, malnutrition, leukemia, and cancer.
• Taking costosteroids and certain medications, underactive adrenal glands, problems with the thyroid gland, and removal of the spleen can also cause an increase in white blood cell levels.

Absolute platelet count

• High platelet levels can occur due to bleeding, iron deficiency, cancer and bone marrow problems.

Low performance

Absolute red blood cell count (RBC)

• With anemia, the level of red blood cells decreases. Anemia can be caused by heavy menstrual bleeding, stomach ulcers, colorectal cancer, inflammatory bowel disease, tumors, Addison's disease, thalassemia, lead poisoning, sickle cell disease, or a reaction to certain chemicals and medications. One reason for low red blood cell counts may be removal of the spleen.
• Not getting enough folic acid or vitamin B12 can also cause anemia, such as pernicious anemia, which causes problems absorbing vitamin B12.
• Red blood cell indices and smear microscopy can help find the cause of anemia.

Absolute white blood cell count (WBC)

• Low white blood cell counts may be caused by chemotherapy and reaction to drug treatment, aplastic anemia, viral infections, malaria, alcoholism, AIDS, lupus, Cushing's syndrome.
• An enlarged spleen can reduce white blood cell counts.

Absolute platelet count

• Low platelet levels can be caused by pregnancy, immunopathological thrombocytopenic purpura and other diseases that affect the process of generating platelets or destroy them.
• An enlarged spleen can reduce platelet counts.

What can affect the results of the examination?

Reasons why the analysis is not possible or the results will be incorrect:

• When drawing blood, your arm was tied with an elastic tourniquet for a long time.
• Taking drugs that cause low platelet counts, such as certain antibiotics, steroids, thiazide diuretics, chemotherapy drugs, quinidine, meprobamate.
• Very high levels of white blood cells or fats (triglycerides) can cause falsely high hemoglobin levels.
• With an enlarged spleen, the level of platelets (thrombopenia) or white blood cells may be reduced; this condition can also cause some types of cancer.
• During pregnancy, the level of red blood cells is often reduced, and less often, the level of white blood cells is increased.

On a note:

• The absolute white blood cell count can reach up to 2000 WBC per microliter due to exercise, stress or smoking.
• Children tend to have higher levels of white blood cells than adults.
• Often, a red blood cell count test includes:
• Erythrocyte sedimentation rate (ESR). The ESR test measures how quickly red blood cells settle to the bottom of a tube. During inflammatory processes occurring in the body (for example, in the presence of infection or cancer), red blood cells settle more slowly than under normal conditions. Using ESR analysis, inflammatory diseases can be diagnosed if the blood test results are normal.
• Analysis of reticulocyte content. This is an analysis of the number of young red blood cells in a blood sample. As a rule, the content of reticulocytes is lower compared to the content of mature red blood cells. However, recent bleeding or destruction of mature red blood cells may cause increased reticulocyte production. This test is done to detect certain types of anemia and screen for the body's response to treatment.
• Hematocrit measurements may vary depending on the assay method and equipment used.

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.

What exactly is determined during the analysis process?

cells (RBCs) are red blood cells. Not only their quantity matters, but also their size, shape and saturation with hemoglobin (Hb) , a protein that carries oxygen and ensures oxygen exchange in the body.

Hematocrit (Ht) is the proportion of red blood cells as a percentage of the total blood volume, a necessary indicator for diagnosing anemia.

MCV is the average erythrocyte volume, useful in diagnosing the causes of anemia.

MCH - the average hemoglobin content in one red blood cell will additionally indicate the presence of anemia.

MCHC - the degree of saturation of erythrocyte hemoglobin is relevant in the diagnosis of anemia associated with iron deficiency.

Relative red blood cell distribution width (RDW) is a measure of the distribution of red blood cells throughout the blood volume.

Platelets (PLT) , cytoplasmic fragments of megacryocytes involved in the formation of a blood clot to stop bleeding, are produced in the bone marrow every 7–10 days. If a low platelet count is obtained during an automated study, it is necessary to exclude the phenomenon of EDTA-induced thrombocytopenia - cell gluing into aggregates; for this purpose, microscopy of a blood smear is performed with counting the number of platelets and assessing the presence of aggregates.

White blood cells (WBC) are cells of the immune system, various in function, expressed in the leukocyte formula. With the normal version of the leukoformula, the percentages of different populations are not disturbed: neutrophils, monocytes, lymphocytes, basophils, eosinophils are in their reference values. The presence of atypical or immature forms of cells in the blood sample is necessarily reflected in the result form.

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.