Basic classification principles
Anemia is not merely an isolated lab abnormality, but a complex typical form of pathology. In clinical practice and pathological physiology, anemias are differentiated according to several main criteria. The fundamental vectors of evaluation include:
- Etiological factors (root causes of the pathology's development).
- Pathogenetic mechanisms (features of the onset and progression of the disease).
- Clinical syndromes (the set of symptoms accompanying anemia).
For precise laboratory diagnosis, morphological criteria are used: the degree of cell pigment saturation, their physical size, as well as the rate of pathological development and the bone marrow response to erythrocyte loss.
By the degree of erythrocyte hemoglobin saturation
This criterion reflects the "density" of cell filling with the respiratory pigment. Evaluation is performed using the classical color index (CI), traditionally used in domestic medicine, or the modern international index MCH (mean corpuscular hemoglobin).
Three types of anemia are distinguished by chromia:
- Normochromic: physiological saturation. The CI is in the range of 0.85–1.05, and the MCH is 27–33 pg.
- Hypochromic: cells with a marked pigment deficiency. The CI drops below 0.85, and the MCH index falls below 27 pg.
- Hyperchromic: hemoglobin-supersaturated cells. The CI exceeds 1.05, and the MCH is greater than 33 pg.
By erythrocyte diameter and volume
The size of red blood cells is a crucial diagnostic marker. It is assessed visually by a laboratory physician based on the cell diameter in a stained blood smear or automatically using a hematological analyzer via the MCV index (mean corpuscular volume).
- Microcytic: abnormally small cells. The diameter is less than 7 µm, and the MCV volume drops below 80 fL.
- Normocytic: standard dimensions. The diameter varies from 7 to 8 µm, and the MCV index remains within 80–100 fL.
- Macrocytic: giant cells. The diameter exceeds 8 µm, and the MCV volume increases to more than 100 fL.
Note: If red blood cells of completely different sizes are simultaneously detected in a patient's blood smear, this pathological phenomenon is called anisocytosis (from Greek an — absence of something, iso — equal, cytos — cell).
By the acuteness of the course and the degree of compensation
The rate of development of the pathological process directly affects the severity of the clinical picture and the body's adaptive capabilities. According to the acuteness of the course, the following are distinguished:
- Acute anemia: a catastrophic condition that develops rapidly, within a few days.
- Chronic anemia: an indolent process that forms gradually—over several weeks, months, or even years.
Classification by degree of compensation This parameter is entirely based on the functional ability of the bone marrow to generate new cells and adequately replace destroyed erythrocytes.
- Compensated: bone marrow reserves are sufficient, so hematological parameters remain within the physiological norm.
- Uncompensated: resources are depleted, the bone marrow cannot cope with the increased load, and hematological parameters inevitably go beyond the normal range.
Briefly: answers to topical questions
What types of anemia are distinguished depending on the etiological factor?
Depending on the etiological factor, three major groups of anemia are distinguished:
- Posthemorrhagic — occur as a result of acute or chronic blood loss;
- Dyserythropoietic — develop due to insufficient erythrocyte production;
- Hemolytic — caused by enhanced erythrocyte destruction.
What groups are anemias divided into according to the pathogenetic mechanism of development?
According to the pathogenetic mechanism of development, anemias are classified into two large groups (with subgroups):
- Anemias due to blood loss or erythrocyte destruction:
- Posthemorrhagic;
- Hemolytic.
- Anemias due to insufficient erythrocyte reproduction:
- Dyserythropoietic;
- Hypoplastic;
- Aplastic.
How are anemias classified according to the regenerative capacity of the bone marrow (reticulocyte count)?
According to the regenerative capacity of the bone marrow, which is assessed by the relative and absolute reticulocyte count, the following groups of anemias are distinguished:
- Hyporegenerative (aregenerative);
- Normoregenerative;
- Hyperregenerative.
To avoid confusing the indices: MCH (Hemoglobin) indicates hemoglobin content and color (chromia), while MCV (Volume) reflects cell volume and size (cytarity).
Class and exam questions
Does the erythrocyte count always decrease in anemia?
No, not always. Although anemia is combined with erythropenia in most cases, exceptions exist. In thalassemia and certain iron-deficiency anemias, the erythrocyte count may remain normal or even be elevated.
What is the fundamental difference between anemia and erythropenia?
Anemia is a pathology in which the amount of hemoglobin must decrease. Erythropenia is a condition in which only the erythrocyte count drops in the blood, while the hemoglobin concentration inside them remains completely normal.
What does the term "anisocytosis" mean in a laboratory report?
This means the simultaneous presence of erythrocytes of different sizes in a blood smear. The term is derived from Greek words literally meaning "absence of identical cells."
How does the bone marrow affect the degree of anemia compensation?
The degree of compensation directly depends on the bone marrow's ability to replace destroyed cells with newly formed ones. If it copes with this task, blood parameters remain normal (compensated form).
What else to study on this topic
- Pathogenetic mechanisms of anemia development
- Etiological factors of anemia
- Clinical syndromes in anemias
- Bone marrow compensation mechanisms
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