They are erythrocytes that have assumed the shape of a sphere rather than the normal discoid shape.
As a result, they appear in routine blood tests as cells that are smaller and denser than normal red blood cells of the species, and have a reduced area of central pallor.
There are several causes of spherocyte formation and the numbers are important to some extent.
In spherocytosis diagnosed for immunity-mediated hemolytic anemia (IMHA), low amounts of spherocytes can be observed in conditions other than IMHA, therefore the presence of spherocytes (especially if it is low amounts) is not always indicative of IMHA .
Other acquired diseases typically have low numbers of spherocytes including fragmentation anemias, oxidative damage to red blood cells (although the cells are actually pycnocytes), coral snake poisoning, and disorders associated with abnormal macrophage function. (hemophagocytic syndrome, histolytic sarcoma) and bee stings.
Red blood cells transfused or stored in blood bags will lose surface area on storage and, when transfused, will appear as spherocytes on the recipient’s blood smears.
In this situation, moderate to many spherocytes can be seen, depending on the proportion of donor cells transfused to the patient’s own cells.
Background information for spherocytes
Spherocytes are red blood cells that have a molecular defect in one or more proteins in the cytoskeleton of red blood cells.
Due to its defect in the cytoskeleton, the RBC contracts with its most efficient and least flexible configuration of surface tension, which is the shape of a sphere (as the name implies).
However, this configuration is susceptible to high osmotic brittleness and prone to physical degeneration.
The appearance of numerous spherocytes without other abnormal red cells in a PBF is highly indicative of hereditary spherocytosis.
If a small number of spherocytes are seen along with other abnormal red blood cells in PBFs, the following clinical conditions may be suspected:
- Isoimmune and autoimmune hemolytic anemias.
- Heinz’s bodily hemolytic anemia.
- Hereditary pyropoikilocytosis.
- Microangiopathic hemolytic anemia.
- Myelofibrosis with myeloid metaplasia.
- Liver disease
- Recent transfusions.
- Severe burns
The hallmark of spherocytes is the presence of numerous small red blood cells that appear synonymous with a sphere shape without a visible central pallor and stain more densely than their normal counterparts.
The denser staining is due to the normal concentration of hemoglobin that becomes “concentrated” due to the contraction of the red blood cells.
The diagnosis of hemolytic anemia is made when the survival of circulating red blood cells is shortened.
Today, laboratory findings in hemolytic anemia and the distinction between inherited and acquired forms are studied by students of preclinical medicine around the world.
Although hemolytic anemia is much less common than anemia as a result of marrow failure or bleeding, general practitioners are well acquainted with the characteristic findings of the condition, and by the time the patient is seen by a hematologist, the diagnosis is already in place. done.
Among the spherocytic hemolytic anemias, hereditary spherocytosis is the most common hereditary hemolytic anemia and autoimmune hemolytic disease is the most common acquired form.
The two diseases share many characteristics known to physicians since the early 20th century, such as: jaundice and splenomegaly on physical examination, spherocytes and reticulocytosis on blood test, increased osmotic fragility of red blood cells, and clinical improvement after splenectomy.
This constellation of clinical features was generally referred to as hemolytic or acholuric jaundice (jaundice) which refers to the characteristic absence of bile in the urine.
A congenital or familial form of hemolytic anemia was often diagnosed in children with a family history of jaundice, splenomegaly, or hemolytic anemia.
However, spontaneous cases in children without a family history and the initial onset of the disease in adults were common enough to cause confusion, as acquired cases were often diagnosed on the basis of acuity and the absence of a family history. in adult patients.
No one seriously questioned the existence of familial or congenital forms of hemolytic anemia, but many questioned the existence of acquired forms other than those that are obviously the result of infection or toxic exposure.
It was not until the rediscovery of the principle of antiglobulin testing and its application to the diagnosis of patients with spherocytic hemolytic anemia that the existence of acquired spherocytic hemolytic anemia and the means to easily distinguish inherited and acquired forms was accepted.
Perhaps it is a unique aspect of these disorders that the underlying principles of our current best diagnostic tests, i.e. blood film spherocytes, osmotic brittleness test, and antiglobulin test, have been known for nearly a century or more. and apply. with some refinements, for more than half a century.