Complete blood count involves measuring the following parameters:
-number of leukocytes;
-number of erythrocytes;
-erythrocyte indices: mean corpuscular volume (MCV), mean erythrocyte hemoglobin (MCH), mean hemoglobin concentration (MCHC) and red cell distribution width (RDW);
-platelet count and platelet indices: average platelet volume (VTM) and platelet distribution width (PDW);
-white blood count;
– +/- number of reticulocytes.
Blood count is a basic screening test is one of the most frequently requested laboratory tests, often representing the first step in determining hematologic and non-hematologic status and hematological diagnosis of various diseases. Quantification of hematological parameters associated sometimes with blood smear brings valuable information, directing continue to perform other tests.
Blood count can be collected while fasting and postprandial (should still avoid high fat meals that may interfere with certain blood count parameters).
Erythrocytes (red blood cell count)
The number of erythrocytes is the base test for evaluating erythropoiesis. Red blood cells are further investigated by measuring the concentration of hemoglobin and hematocrit, and on this basis the analyzer calculates erythrocyte indices: MCV, MCH, MCHC and RDW, which characterize qualitatively the erythrocyte population.
Red blood cells are the most numerous blood cells, they do not have a nucleus, they are needed for tissue respiration. Red blood cells are the specialized cells of the body, the main function consisting of 02 transport from the lungs to the tissues and transfer of CO2 from the tissues to the lungs. This is done by hemoglobin contained in erythrocytes. The shape of erythrocytes, that of biconcave disc shape gives the ratio volume / surface for optimal gas exchange and provide them deformability during the crossing of microcirculation.
Indications – in combination with hematocrit and hemoglobin concentration, erythrocyte count is useful in detecting and monitoring anemia and erythrocytosis / polycythemia.
Hematocrit (volume of cell package )
Hematocrit measures the ratio of the volume occupied by red blood cells and total blood volume.
Directions – detection and monitoring of anemia and polycythemia.
Hematocrit red blood cells depends on erythrocyte mass, corpuscular volume and plasma volume.
Usually, when red blood cells are normal size, hematocrit changes follow those in the number of erythrocytes. However in anemia micro- / macrocytic relationship cannot be kept. For example, in thalassemia hematocrit decreases as microcytic red cells occupy a smaller volume, while the number of erythrocytes can be normal / increased.
1. Hematocrit decrease:
– Anemia; a Hct <30% (0.30) a patient is moderate – severe anemia;
– Increased plasma volume (load).
2. Increased hematocrit:
– erythrocytosis / polycythemia;
– hemoconcentration (ex .: shock, inadequate fluid intake: young children, the elderly, polyuria, etc.).
Hemoglobin is the main component of red blood cells (95% of the red cell cytoplasmic proteins) and serves as a vehicle to transport O2 and CO2.
Indications – with Hct and RBC count is useful for detecting and monitoring anemia and polycythemia.
Reference values - different according to age and sex (see Annex 7.1.1). Hb is expressed in g / L or g / dL.
The number of erythrocytes, Hb and Hct can be analyzed by applying the “rule of three” if erythrocytes are normocyte / normochromic: no. Er x3 ~ Hb value.
Hematocrit hemoglobin can be estimated from the following formula:
Hct = Hb (g / dL) x 2.8 + 0.8 or Hct = Hb x 3 .
Evaluation of erythrocytes in terms of volume and hemoglobin content is done by measuring or calculating the following parameters:
– Medium corpuscular volume (MCV) – is the volume occupied by a single erythrocyte.
– The method of determination – VEM is calculated according to the following formula: Hct (%) x 10
VEM = ——- Nr.Er. (x106 / ¶l)
Through the automatic method VEM is determined by dividing the sum of erythrocyte volumes to the erythrocyte number.
Reference values - VEM is expressed in cubic micrometers or femtoliters (FL). In adults is between 80-100 fL (higher values in newborns and the elderly; lower values in children up to 18 years – see Annex 7.1.1).
Clinical significance :
VEM is a useful index for classification of anemia and may suggest pathophysiological mechanism of erythrocyte damage. Together with the other red cell indices it may allow early detection of processes that will cause anemia. VEM depends on the plasma osmolarityand the number of erythrocyte divisions.
Medium erythrocyte hemoglobin (MCH) – is a measure of the average content of hemoglobin in erythrocytes.
Method for determining HEM – it is calculated by the automatic analyzer according to the formula: Hb (g / dL) x 10.
HEM = ——- Nr.Er. (x106 / ¶l)
Reference values - HEM is expressed in picograms (pg / 10-12g). Normal values are adult or 0.4-0.53 pg 26-34 fmol (higher values in the newborn; see Appendix 7.1.1).
Medium erythrocyte hemoglobin concentration (MCHC) – measures the average concentration of hemoglobin in a given volume of erythrocytes (or Hb ratio of mass and volume of red blood cells).
Method for determining CHEM – it is calculated by the automatic according to the formula: Hb (g / dL) x 100.
CHEM = ——- Hct (%)
Reference values - CHEM is expressed in g / dL. Normal values in adults are 32-36 g / dL (320-360 g / L) (see Annex 7.1.1).
Red cell distribution width (RDW) – is an index that quantifies the heterogeneity of erythrocyte cell volume (degree of anisocytosis).
The method of determination – RDW is calculated by the automatic analyzer according to the presence of relative frequency of abnormalities at certain levels of discrimination, the existence of two or more “peaks” and abnormal width distribution. VEM distribution in a sample is shown as a graph in which on the abscissa is projected the corpuscular volume, and on the ordinate relative frequency. Standard deviation of the size of erythrocytes x 100
RDW (CV%) = ——————— VEM
Reference values - 11.6-14.8 coefficient of variation (CV) of corpuscular volume.
Reticulocytes are young, immature erythrocytes with no nucleus, containing residual nucleic acids (RNA). After expulsion of the nucleus erythrocytes remain in the spinal nucleus op to 4 days, during which there is a continuous decrease in the number of polyribosomes (containing RNA) and hemoglobin synthesis. These young erythrocytes mature completely in peripheral blood,approx. 1-2 days after leaving the bone marrow.
Reticulocytes appear on Wright-Giemsa stained smears as polychromatophilic cells (reticular nucleic material is colored in blue-gray) volume greater than the mature erythrocytes. Reticular material is colored with brilliant cresyl/ methylene blue blue dye as supravital colorants. Normally, in the absence of anemia, a small number of reticulocytes is currently in circulation (every day ~ 1% of the erythrocytes are replaced with young erythrocytes obtained from the bone).
Determining the number of reticulocytes provides information about bone marrow’s ability to synthesize red cells in response to physiological strain, such as anemia
1. Differentiate types of anemia in: regenerative and non-regenerative / hyper-regenerative.
2. Monitoring response to substitution treatment with iron, folic acid / vitamin B12.
3. Evaluation of erythropoiesis after bone marrow transplantation in aplastic anemia induced by cytotoxic / or treatment with erythropoietin.
Method of determination
1. Method Manual – microscopic counting.
Adult: 0.5-2% of no. Er total.
Platelets (platelet number)
Platelets are cytoplasmic fragments with no nucleus granules , rich in granules , round-oval, flat, disc-shaped with a diameter of 2-4μ. Thrombopoeisis occurs in the bone marrow beginning with the multipotent progenitor cell , continuing with megakariocytopoiesis, including proliferation and maturation of megakaryocytes with platelet formation.
Normally, two thirds of platelets are found in circulation, and a third are stored in the spleen. Platelets are involved in hemostasis and tissue repair processes, in the initiation and vasoconstriction after vascular injury during inflammatory processes, adherence and platelet aggregation resulting in platelet thrombus formation in vessel walls that stop small tears.
– investigation of unexplained bleeding, hemorrhagic disease or thrombotic diseases;
– in a coagulation profile;
– monitoring of diseases associated with bone marrow failure;
– monitoring during treatment may induce myelosuppression (radiation, chemotherapy, etc.)
Method of determination – platelets are counted by the automatic analyzer by the same method as erythrocytes during their targeting a single row through a hole by the method of hydrodynamic focusing.
An estimate of the number of platelets in a blood smear well done is a valuable control of platelets caused by automatic method. Generally, when the smear is examined with the objective of each platelet observed 100x / Tr field is ~ 10,000 x106 / L. Consequently, a normal smear must submit averaged at least 14 Tr / field.
Reference values – 150-450 x 103 / ìl.
1. Increased platelet counts (thrombocytosis / thrombocythemia)
A transient Thrombocytosis – is due to mobilization platelet extravascular pool: exercise, childbirth, administration of epinephrine.
B. primary thrombocytosis:
Hereditary thrombocythemia (rare, autosomal dominant ; thrombopoietin gene mutation on chromosome 3).
Myeloproliferative syndromes (clonal hematopoiesis): essential thrombocythemia, polycythemia vera, chronic myelogenous leukemia, myeloid metaplasia with myelofibrosis.
C. Secondary / reactive thrombocytosis (persistent production of one or more thrombopoietic factors in special interleukin 6, which acts on megakaryocytes):
-rapid regeneration after hemorrhage / hemolytic anemia;
-rebound after rebuilding post-thrombocytopenia;
-anatomic asplenia (splenectomy) / functional (eg sickle cell anemia);
2. Decreased platelet count (thrombocytopenia) is the most common cause of bleeding. Thrombocytopenia can occur by different mechanisms:
A. accelerated platelet destruction : it is the most common cause of thrombocytopenia; this causes thrombopoeisis stimulation leading to increases in number, size and maturation of bone marrow megakaryocytes.
B. Low production of platelets:
C. Distribution abnormal platelets:
-Diseases of the spleen (neoplastic, congestive, infiltrative, infectious); usually mild thrombocytopenia = 50-100 × 103 / ìl.
-Dilution of platelets by massive transfusions.
Many drugs have been associated with immune thrombocytopenia. The most common damaging drugs are: heparin (1% of patients), quinidine, quinine, rifampin, trimethoprim-sulfamethoxazole, danazol, methyldopa, acetaminophen, digoxin, interferon-alpha, etc.
Thrombocytopenia is clinically associated with mucous-cutaneous bleeding: petechiae, purpurae, gum bleeding, epistaxis, gastrointestinal bleeding, lung and genital- urinary bleeding. Spontaneous bleeding is rare to> 60 × 103Tr / ¶l (traumatic bleeding may occur, postoperative).
WBC (white blood cells), and leukocytes
Leukocytes are divided into two main groups: granulocytes and non-granulocytes. Granulocytes are named so because of the presence in the cytoplasm of different grain sizes and we can identify three types of granulocyte staining affinities depending on stained Wright blood smears: neutrophils, eosinophils and basophils.
In addition, these cells are also referred to as polymorphonuclear leukocytes due to their multi-lobe core. Nongranulocytes consisting of lymphocytes and monocytes do not generally contain distinct cytoplasmic granulations and have non- lobe nucleus, also being called mononuclear leukocytes.
Directions – evaluation of infection, inflammation, tissue necrosis, poisoning, allergies, chronic myeloproliferative disorders and acute and chronic lymphoproliferative malignancies, bone marrow depression (irradiation, cytotoxic agents, immunosuppressants, antithyroid etc.).
Method for determination – leukocytes are determined by automatic analyzer (after red blood cells are lysed and leukocytes are stained with a fluorescent substance with affinity for nucleic acids) through the flow cytometry method using semiconductor laser fluorescence.
Reference values - adult = 4000-10000 / ¶l or 4-10 × 109 / L;
Clinical significance :
2. Leukocytosis: L> 10,000 / ¶l or> 10 × 109 / L – is usually due to an increase in the number of neutrophils or lymphocytes; less other classes of leukocytes causes increased absolute number of leukocytes. A proportional increase in all types of leukocytes is due to hemoconcentration .
a. Infection is a major cause of leukocytosis.
b. Other causes of leukocytosis:
trauma / injury of tissue, such as surgery, tissue necrosis;
malignant tumors (in particular bronchial carcinoma);
toxins, uremia, eclampsia, coma, thyrotoxicosis;
drugs: chloroform, quinine, growth factors, etc .;