What Are Target Cells and Crystals in Hemoglobin C?

When you look at your blood test results (often called a peripheral blood smear), seeing terms like “target cells” and “crystals” can be confusing. However, these terms simply describe the physical shape and appearance of your red blood cells under a microscope.

It is important to note that these specific findings—particularly crystals and the resulting mild anemia—are features of Hemoglobin C disease (having two copies of the gene), rather than Hemoglobin C trait (having one copy), which usually does not cause these structural changes ^[1].

Because of the specific genetic change in Hemoglobin C disease, your red blood cells tend to lose water and become dehydrated ^[1][2]. (Note: This is an internal cellular process caused by the hemoglobin itself; drinking more water will not fix or change this cellular dehydration.) This dehydration causes the cells to flatten out and look like bullseyes (target cells), and it causes the hemoglobin inside them to clump together into solid shapes (crystals) ^[3][4].

Why Do Red Blood Cells Dehydrate?

In a typical red blood cell, hemoglobin (the protein that carries oxygen) stays completely dissolved in water, keeping the cell round, plump, and flexible. However, the genetic mutation that causes Hemoglobin C disease changes the chemical structure of the hemoglobin, making it less soluble ^[1][5]. This altered hemoglobin triggers the red blood cells to lose water and become dehydrated ^[6][7]. This dehydration alters the physical dynamics of the cell membrane, making the cells look different on a lab report ^[7][8].

What Are Target Cells?

Target cells are red blood cells that literally look like a shooting target or a bullseye under a microscope ^[7][8]. When a red blood cell loses water and shrinks, the outer membrane of the cell becomes relatively large compared to the smaller volume of fluid inside. This extra membrane essentially bunches up, creating a dark center dot of hemoglobin surrounded by a pale ring, with another dark ring on the outside ^[7]. Seeing target cells on a blood smear is extremely common in Hemoglobin C disease and is a direct physical result of cellular dehydration ^[7][8].

What Are Hemoglobin Crystals?

Hemoglobin crystals form when the abnormal hemoglobin C protein binds together into solid structures ^[7]. Because the hemoglobin C protein is less able to stay dissolved in liquid, it tends to stick together and form solid, rod-shaped or hexagonal (six-sided) blocks inside the cell ^[1][3]. This crystallization process happens much more frequently when the red blood cell is dehydrated ^[2][4]. When a pathologist examines your blood smear under a microscope, these rod-shaped crystals are a distinct and defining feature of Hemoglobin C disease ^[3][4].

How Does This Affect Your Body?

These physical changes—dehydration, target cells, and crystal formation—make your red blood cells stiffer and less flexible than normal ^[1][4]. Normal red blood cells need to be highly flexible to squeeze through tiny blood vessels, particularly in the spleen, which acts as a filter for your blood.

Because cells containing hemoglobin crystals lose their ability to bend and stretch, they often get trapped in the spleen ^[1][4]. Once trapped, these stiff cells break down much earlier than healthy red blood cells ^[1][2]. This premature destruction of red blood cells is called hemolysis ^[1].

While your body continuously produces new red blood cells to replace the ones that are destroyed, this ongoing early breakdown is what causes the mild chronic hemolytic anemia (a lower than normal red blood cell count) often seen in Hemoglobin C disease ^[7][8]. This might lead to mild fatigue, occasional yellowing of the eyes or skin (jaundice), or an enlarged spleen ^[1]. However, most people with Hemoglobin C disease manage the condition very well and enjoy a normal life expectancy ^[7][1].