Renato Faillace, MD. Hematology Specialist by the Brazilian Medical Association.

(from Greek, an = privation, haima = blood) is said to occur when the concentration of blood hemoglobin decreases beyond the levels established by the World Health Organization at 13 g/dL for men, 12 g/dL for women, and 11 g/dL for pregnant women and infants between 6 months and 6 years old.

What's hemoglobin

Hemoglobin is the pigment that colors the red blood cells (erythrocytes) and has the vital function of transporting oxygen from the lungs to the tissues.

Despite having a set of peculiar symptoms and signs, anemia is not a disease per se, but a syndrome, as it may arise from an extensive list of causes.

It is the chronic syndrome of highest prevalence in clinical medicine.

Classification of anemia

Anemia can be either acute or chronic.

In acute anemia (sudden loss of blood), the lack of blood volume in the circulatory system is more important than the deficiency of hemoglobin. A loss up to 10% of blood volume, as that taking place upon blood donation, is well tolerated. Losses between 10 and 20% cause postural hypotension, dizziness and faint. In losses above 20%, there's tachycardia, cold extremities, extreme paleness and hypotension, followed by shock; should the loss surmount 30%, without immediate replacement of intravenous fluids, the shock rapidly becomes irreversible and fatal.

In chronic anemia, there's no decrease in blood volume, which is compensated by an increase in plasma volume.

The lack of hemoglobin, as a rule accompanied by a decreased number of erythrocytes, its transporting cells, causes the blood to discolor, with paleness in the patient, and lack of oxygen in every organ, with the resultant clinical signs. Hypocrates (in 400 B.C.) described them: paleness and weakness are due to blood corruption.

The central nervous system, the heart and the muscle mass are the most affected organs, since they are the ones that most need oxygen for their functions.

The symptoms increase with physical activity, as this consumes oxygen.

With hemoglobin between 9 and 11 g/dL there's irritability, headache and psychic asthenia; in the elder fatigability is observed, and angina may occur.

With hemoglobin between 6 and 9 g/dL there's tachycardia, dyspnea and fatigue upon the slightest effort.

With hemoglobin below 6 g/dL symptoms are present even in sedentary activities, and when below 3.5 g/dL heart failure is impending and any activity is unfeasible.

The patients' spontaneous complaints, however, are less exuberant that the description above: without realizing it, they gradually decrease their physical activity down to asymptomatic levels, and state they don't feel anything.


The hemogram is the key exam for anemia diagnosis. It's currently undertaken in sized and highly costly (from US$ 80000 up to US$ 400000) electronic counters that count and measure the erythrocytes, generating frequency curves with means and variation coefficients, determining the numeric parameters of the erythroid population. The best devices discern and count the younger erythrocytes (reticulocytes), allowing, thus, an assessment of both the daily production and the regenerative response to anemia.

Supplementing the figures from this terrific technology with microscopic observation by an experienced clinical pathologist, most anemia cases can be characterized according to their causative mechanism (pathogenesis), which leads to the diagnosis of the illness or the underlying causative event (etiology). Therefore:

When the pathogenesis is the inadequate production of hemoglobin, due to either iron deficiency or genetic defect in the synthesis, the hemogram will reveal the presence of erythrocytes that are smaller than the normal size (microcytosis), as they lack content.
In the anemias resulting from erythroid proliferation inhibition, as in vitamin B12 deficiency, in the use of antiblastic drugs (used for cancer treatment), or in some diseases peculiar to the bone marrow, are noted erythrocytes with a mean volume greater than the normal one (macrocytosis).
In the anemias that accompany infectious, rheumatic, renal, endocrine, chronic diseases, the hemogram is characterized as "not being elucidative"; clinical signs and exam results peculiar to each one of them must be sought.
In the anemias by excess peripheral destruction of erythrocytes (hemolytic anemia) and on the days following a hemorrhage, the hemogram will show a significant increase in the reticulocyte counts, characterizing the reactive hyperregeneration of the erythroid tissue of the marrow.

Types of anemia

The most frequent anemias and/or of particular medical and social importance are:

Iron deficiency anemia (ferropenic anemia)


Vitamin B12 deficiency anemia (pernicious anemia) and folic acid anemia


Chronic disease anemia


Anemia by genetic defects

– sickle cell anemia

– thalassemia

– spherocytosis

– glucose-6-phosphate-dehydrogenase deficiency (favism)

Anemias by peripheral aggression to the erythrocytes:

– malaria

– autoimmune hemolytic anemia

– erythrocyte fragmentation anemia

Anemias resulting from bone marrow diseases:

– aplastic anemia

– leukemia and marrow tumors