Concept of the hemogram
A hemogram is a complete blood count that includes the study of the count of all formed elements, their morphological features, erythrocyte sedimentation rate, hemoglobin concentration, color index, hematocrit, and the ratio of different types of leukocytes. Knowledge of normal blood parameters is a fundamental requirement in any clinical department: a complete blood count is the primary laboratory test ordered in the vast majority of pathologies.
Reference ranges are targeted at the average adult; in children, high-altitude residents, and specific population groups, normal parameters may vary significantly, so interpretation is always performed taking the individual context into account.
Red blood cell parameters
Changes in red blood cells are evaluated based on three parameters: concentration, size, and shape of erythrocytes.
- Anemia is a decrease in hemoglobin and erythrocyte levels. It occurs in iron deficiency, vitamin B12 deficiency, leukemias, and chronic diseases. On a blood smear, erythrocytes are hypochromic, reduced in size, with an expanded central pallor.
- Polycythemia (erythrocytosis) is an increase in erythrocyte concentration. It can be an adaptive response (e.g., in high-altitude residents under low partial pressure of oxygen) or a manifestation of pathology.
Based on size, the following are distinguished:
- Macrocytes are erythrocytes with a diameter greater than 9 µm; macrocytosis is characteristic of B12-deficiency anemia.
- Microcytes are erythrocytes with a diameter of 6 µm or less; microcytosis accompanies iron-deficiency states.
- Anisocytosis is the presence of erythrocytes of varying sizes in the blood.
Normally, an erythrocyte has the shape of a biconcave disc. The appearance of abnormally shaped erythrocytes is called poikilocytosis: echinocytes (with spiky projections), spherocytes (rounded, having lost biconcavity), dacryocytes (teardrop-shaped), stomatocytes (with a slit-like central pallor resembling a mouth).
Reticulocytes and erythropoiesis
The clinical analysis also evaluates the count of reticulocytes — immature erythrocytes entering the bloodstream. In addition to them, normocytes (orthochromatophilic erythroblasts — synonymous terms) may be encountered.
During erythropoiesis, the content of nucleic acids decreases while the amount of hemoglobin increases: early cells stain basophilically, and as hemoglobin accumulates, the cell becomes oxyphilic. Understanding the stages of erythropoiesis is essential for the correct interpretation of the appearance of immature forms in peripheral blood.
The erythrocyte sedimentation rate (ESR) is measured by placing anticoagulated blood in a graduated tube: erythrocytes settle in the form of "rouleaux". The normal value is 5–9 mm/h. An elevated ESR is a non-specific marker of inflammation that can increase manifold in a number of pathologies.
Platelets
The normal platelet concentration is 200–400 thousand cells per microliter. Two pathological states are distinguished:
- Thrombocytopenia is a decrease in platelet count below 100 thousand/µL. It is observed in congenital and acquired abnormalities, and disorders of red bone marrow activity. Clinically manifested by spontaneous bleeding and small hemorrhages that respond poorly to therapy.
- Thrombocytosis is an increase in platelet concentration. It can be physiological (after blood loss — compensatory release of platelets from the red bone marrow) or pathological in systemic diseases.
White blood cell differential and its shifts
A left shift of the white blood cell differential is a condition in which immature leukocytes enter the peripheral blood: metamyelocytes, myelocytes, less commonly myeloblasts. Most frequently observed in inflammatory reactions.
During granulocytopoiesis, sequential differentiation takes place: first, non-specific and specific granules are synthesized, then the proportion of specific granules characteristic of a particular cell type (neutrophil, eosinophil, basophil) increases. Concurrently, the capacity for division is lost, the nuclear shape changes (segments appear), and the number of organelles and overall cell size decrease.
Changes in specific types of leukocytes
- Neutrophils. Neutrophilia occurs during an enhanced release of cells from the bone marrow in acute, most commonly bacterial infections. Neutropenia can be physiological or accompany recurrent infectious lesions due to reduced microphagocytosis.
- Basophils. Basophilia is noted in hypersensitivity reactions, post-irradiation, in hypothyroidism, and systemic blood diseases.
- Eosinophils. Eosinophilia is characteristic of helminthic infestations and allergic conditions (bronchial asthma, allergic rhinitis, dermatitis). A decrease in eosinophil count is observed in acute infections and following the administration of glucocorticoids with immunosuppressive action.
- Monocytes. Monocytosis is a manifestation of inflammatory diseases. Monocytopenia occurs in aplastic anemias, leukemias, and during immunosuppression.
- Lymphocytes. Lymphocytosis is characteristic of viral infections, tumors, hypersensitivity reactions, and thyrotoxicosis. Physiological lymphocytosis is observed in children under 4–5 years of age, when the lymphocyte count exceeds the neutrophil count. Lymphocytopenia accompanies severe prolonged infections, oncological diseases, aplastic anemia, autoimmune disorders, HIV infection, and radiation exposure.
The neutrophil-to-lymphocyte ratio helps to roughly assess the nature of the infection: a predominance of neutrophils indicates a bacterial etiology, while lymphocytes indicate a viral etiology.
Key points
- The hemogram includes a quantitative and morphological evaluation of formed elements, ESR, hemoglobin, hematocrit, and the white blood cell differential.
- Red blood cell changes are analyzed along three axes: concentration (anemia/polycythemia), size (micro-/macrocytosis, anisocytosis), and shape (poikilocytosis).
- An elevated ESR is a non-specific but sensitive marker of an inflammatory process.
- Thrombocytopenia below 100 thousand/µL is clinically significant and is accompanied by hemorrhagic syndrome.
- A left shift of the white blood cell differential indicates the release of immature granulocytes into the blood and is characteristic of inflammation.
- Neutrophilia is typical for bacterial infections, lymphocytosis for viral infections, and eosinophilia for allergies and helminthiases.
- In children under 4–5 years of age, lymphocytes physiologically predominate over neutrophils.
- Reference ranges are approximate: the patient's age, condition, and living conditions require individual interpretation.