The term “sicklings” can be used informally to refer to sickled red blood cells, also called sickle cells. These are red blood cells that have changed from their normal flexible, disc-like shape into a rigid, crescent- or sickle-shaped form.
The underlying process is called sickling. It occurs when abnormal hemoglobin, particularly hemoglobin S (HbS), causes red blood cells to change shape under certain conditions, especially when oxygen levels are low.
The term is most closely associated with sickle cell disease (SCD), a group of inherited blood disorders affecting hemoglobin.
Normal Red Blood Cells vs. Sickled Cells
Healthy red blood cells are typically round, disc-shaped, and flexible. Their flexibility allows them to travel through both large blood vessels and very small capillaries while carrying oxygen throughout the body.
Sickled cells behave differently. They can become hard, rigid, and sticky, making it more difficult for them to pass through narrow blood vessels.
This difference can be summarized as:
| Normal red blood cells | Sickled red blood cells |
|---|---|
| Flexible and disc-shaped | Rigid and crescent-shaped |
| Move easily through blood vessels | Can obstruct small blood vessels |
| Normal hemoglobin | Abnormal hemoglobin may be present |
| Survive about 90–120 days | Often survive only about 10–20 days in SCD |
The shorter lifespan of sickled cells contributes to anemia in people with sickle cell disease.
What Causes Sickling?
Sickling is primarily caused by abnormal hemoglobin.
Hemoglobin is the protein inside red blood cells responsible for carrying oxygen. In sickle cell disease, genetic changes cause the body to produce abnormal forms of hemoglobin, most notably hemoglobin S.
When oxygen levels become low, hemoglobin S can form stiff strands inside the red blood cell. These strands distort the cell and cause it to develop its characteristic sickle or crescent shape.
The resulting cell is less flexible than a normal red blood cell.
What Is Sickle Cell Disease?
Sickle cell disease is a group of inherited red blood cell disorders caused by abnormal hemoglobin.
People with SCD inherit gene variants affecting hemoglobin production. Different combinations of inherited hemoglobin variants can produce different forms of the disease, including HbSS, HbSC, and HbS beta-thalassemia.
The most common form, HbSS, occurs when a person inherits a hemoglobin S gene from each parent and is commonly referred to as sickle cell anemia.
How Sickling Affects Blood Flow
One of the major problems caused by sickling is obstruction of blood flow.
Normal red blood cells can bend and squeeze through tiny blood vessels. Sickled cells are much less flexible and can become stuck in small vessels. They may also stick to blood vessel walls and to other cells.
When blood flow becomes blocked or slowed, tissues may not receive enough oxygen. This can cause pain crises, one of the characteristic complications of sickle cell disease.
Repeated or prolonged blockage can also contribute to damage affecting different organs.
Sickling and Low Oxygen
Low oxygen is an important factor in the sickling process.
When hemoglobin S is exposed to low-oxygen conditions, it can form rigid structures inside red blood cells. These structures distort the cells and produce the sickle shape.
Sickling can therefore be influenced by circumstances that place additional demands on the body or reduce oxygen availability.
However, people with sickle cell disease can experience sickling and related complications as part of the disease even without an obvious external trigger.
Why Are Sickled Cells Fragile?
Sickled cells are not only rigid; they are also more fragile than normal red blood cells.
Healthy red blood cells generally circulate for approximately 90 to 120 days. In sickle cell disease, sickled cells can survive only around 10 to 20 days before being destroyed.
The body continually produces new red blood cells, but in SCD the destruction of cells can occur faster than they are replaced. This contributes to anemia, meaning there are not enough healthy red blood cells to carry oxygen efficiently.
Symptoms Associated With Sickling
The effects of sickling vary between individuals and depend on the type and severity of sickle cell disease.
Possible complications include:
- Episodes of severe pain
- Anemia
- Fatigue
- Swelling of the hands and feet
- Infections
- Acute chest syndrome
- Stroke
- Organ complications
The CDC notes that sickled cells can block blood vessels and cause serious complications, including pain, infection, acute chest syndrome, and stroke.
Sickling and Pain Crises
A pain crisis, also called a vaso-occlusive crisis, can occur when sickled cells obstruct blood flow.
The resulting reduction in oxygen delivery can cause sudden and sometimes severe pain. Pain crises can last for hours or several days and may require medical treatment.
Not every person with sickle cell disease experiences pain in the same way or with the same frequency.
Sickling vs. Sickle Cell Trait
Sickling should not automatically be equated with having sickle cell disease.
A person with sickle cell trait inherits one sickle cell gene and one gene for normal hemoglobin. Most people with sickle cell trait do not have the chronic symptoms associated with sickle cell disease.
Sickle cell disease generally occurs when a person inherits two relevant abnormal hemoglobin gene variants, although the exact combination can vary.
This distinction is important because sickle cell trait is not the same as sickle cell disease.
How Sickling Is Identified
Healthcare professionals can evaluate sickle cell disease and the type of hemoglobin a person carries through blood testing.
Testing can identify abnormal hemoglobin and help distinguish between different forms of sickle cell disease and sickle cell trait.
In many countries, screening programs can identify sickle cell disease early in life. In the United States, for example, newborn screening is routinely used to identify the condition.
A blood smear may also show abnormally shaped red blood cells, although additional laboratory testing is used to establish the underlying hemoglobin type.
Can Sickling Be Prevented?
Medical treatment for sickle cell disease aims to reduce complications, manage symptoms, and prevent or limit sickling-related problems.
Treatment depends on the person’s condition and may include medications, blood transfusions, and other specialized approaches. Some people may be candidates for blood or bone marrow transplantation, while newer gene therapies are also available for certain patients.
The appropriate treatment is determined by healthcare professionals based on the individual’s type of sickle cell disease and medical circumstances.
The Importance of Hemoglobin
Understanding sicklings requires understanding the role of hemoglobin.
Hemoglobin normally binds oxygen and transports it throughout the body. In sickle cell disease, abnormal hemoglobin changes the physical properties of red blood cells.
Hemoglobin S can form rigid fibers when oxygen levels are low. These fibers cause red blood cells to become distorted, creating the characteristic sickle shape.
Thus, the abnormal cell shape is not simply a surface change. It results from changes occurring within the red blood cell because of abnormal hemoglobin.
Why the Term “Sickling” Is Used
The word sickling comes from the distinctive shape that affected red blood cells develop.
A sickle is a curved agricultural tool. Because affected cells can develop a similar curved or crescent-like appearance, they are called sickle cells, and the process of changing into this shape is called sickling.
“Sicklings” is therefore best understood as a descriptive or informal plural reference to sickling phenomena or sickled cells rather than as the standard name of a separate disease.
Conclusion
Sicklings can refer informally to sickled red blood cells, while sickling is the process through which normally flexible red blood cells become rigid and crescent-shaped because of abnormal hemoglobin.
The phenomenon is most strongly associated with sickle cell disease, an inherited group of blood disorders involving abnormal hemoglobin. When hemoglobin S forms rigid structures under low-oxygen conditions, it can distort red blood cells, making them stiff and sticky. These cells can obstruct small blood vessels, break down prematurely, and contribute to pain crises, anemia, and other complications.
Although “sicklings” is not the usual formal medical term, understanding sickling and sickle cells helps explain the underlying mechanism of sickle cell disease and many of its complications.