leptocyte

Leptocytes are red blood cells characterized by a thin, flattened, or elongated shape with an increased membrane-to-volume ratio. This altered geometry produces excessive central pallor and a delicate, easily deformed appearance on peripheral blood smear, reflecting changes in the cell membrane relative to hemoglobin content.

The term encompasses several morphologies produced by relatively extra membrane. The most familiar forms are target cells (codocytes), which display a central area of dense staining surrounded by a pallor ring and an outer rim of hemoglobin; and stomatocytes, which have a slit- or mouth-shaped region of pallor. Other thin, folded, or elongated erythrocytes may also be described as leptocytes.

Leptocytes are associated with a variety of conditions. Liver disease (including cholestasis and cirrhosis), iron deficiency anemia, thalassemias and other hemoglobinopathies, and post-splenectomy or hyposplenia can all show leptocytes on smear. Lipid disorders and certain drugs that alter membrane composition can also contribute.

Pathophysiology centers on membrane alterations. Increased membrane surface area relative to cytoplasmic volume can result from changes in cholesterol and phospholipid content or defects in the cytoskeletal network, producing a cell with reduced hemoglobin concentration and a higher likelihood of exhibiting the leptocyte morphology.

Diagnosis relies on microscopic examination of a peripheral smear. Leptocytes are not disease-specific but highlight membrane abnormalities that guide further workup, including iron studies, liver tests, and investigations for hemoglobinopathies or splenic function, depending on the suspected underlying condition.