Thalassemia trait, particularly beta-thalassemia trait, is often associated with the presence of target cells on a blood smear. These target cells, also known as codocytes, are characterized by a central dense area surrounded by a lighter ring, resembling a bullseye. In thalassemia trait, this shape arises from an excess of membrane relative to the cell’s volume due to reduced hemoglobin production. [1, 1, 2, 2, 3, 3, 4, 4, 5, 6]

Here’s a more detailed explanation: [3, 3, 4, 4]

What are target cells?

Target cells are red blood cells that appear to have a bullseye-like pattern due to an excess of cell membrane compared to the cell’s volume. [3, 3, 4, 4]

Why are they seen in thalassemia?

In thalassemia, the reduced production of hemoglobin (the oxygen-carrying protein in red blood cells) leads to a cell that’s smaller and paler than normal. This can result in an excess of cell membrane, causing the characteristic target shape. [1, 1, 3, 3, 4, 4, 7, 8, 9]

Alpha-thalassemia and target cells:

Alpha-thalassemia, a condition where there are defects in the alpha-globin protein, can also be associated with target cells, according to the American Medical Association. [10, 10]

Other conditions with target cells:

Target cells are also seen in other conditions like hemoglobin C disease, liver disease, and after splenectomy. [3, 3, 11, 11]

Diagnosis:

While target cells are a common finding in thalassemia, they don’t definitively diagnose the condition. Other tests, like hemoglobin electrophoresis, are needed for a definitive diagnosis. [9, 9, 12, 12]

[1] https://www.aafp.org/pubs/afp/issues/2022/0300/p272.html

[2] https://www.sciencedirect.com/topics/medicine-and-dentistry/thalassemia-minor

[3] https://imagebank.hematology.org/image/60310/target-cells

[4] https://en.wikipedia.org/wiki/Codocyte

[5] https://genemod.net/blog/identifying-target-cells

[6] https://www.jaypeedigital.com/eReader/chapter/9789351521365/ch37

[7] https://www.ncbi.nlm.nih.gov/books/NBK545151/

[8] https://www.contemporaryobgyn.net/view/the-importance-of-identifying-hemoglobinopathy-carrier-status

[9] https://www.merckmanuals.com/professional/hematology-and-oncology/anemias-caused-by-hemolysis/thalassemias

[10] https://www.ama-assn.org/medical-students/usmle-step-1-2/kaplan-usmle-step-1-what-does-blood-smear-reveal

[11] https://www.ncbi.nlm.nih.gov/books/NBK263/

[12] https://www.ncbi.nlm.nih.gov/books/NBK585044/

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