What is poikilocytosis?

Poikilocytosis is the medical term for having abnormally shaped red blood cells (RBCs) in your blood. Abnormally shaped blood cells are called poikilocytes.

Normally, a person’s RBCs (also called erythrocytes) are disk-shaped with a flattened center on both sides. Poikilocytes may:

  • be flatter than normal
  • be elongated, crescent-shaped, or teardrop-shaped
  • have pointy projections
  • have other abnormal features

RBCs carry oxygen and nutrients to your body’s tissues and organs. If your RBCs are irregularly shaped, they may not be able to carry enough oxygen.

Poikilocytosis is usually caused by another medical condition, such as anemia, liver disease, alcoholism, or an inherited blood disorder. For this reason, the presence of poikilocytes and the shape of the abnormal cells are helpful in diagnosing other medical conditions. If you have poikilocytosis, you likely have an underlying condition that requires treatment.

The main symptom of poikilocytosis is having a significant amount (greater than 10 percent) of abnormally-shaped RBCs.

In general, the symptoms of poikilocytosis depend on the underlying condition. Poikilocytosis can also be considered a symptom of many other disorders.

Common symptoms of other blood-related disorders, such as anemia, include:

  • fatigue
  • pale skin
  • weakness
  • shortness of breath

These particular symptoms are a result of not enough oxygen being delivered to the body’s tissues and organs.

Poikilocytosis is typically the result of another condition. Poikilocytosis conditions can be inherited or acquired. Inherited conditions are caused by a genetic mutation. Acquired conditions develop later in life.

Inherited causes of poikilocytosis include:

  • sickle cell anemia, a genetic disease characterized by RBCs with an abnormal crescent shape
  • thalassemia, a genetic blood disorder in which the body makes abnormal hemoglobin
  • pyruvate kinase deficiency
  • McLeod syndrome, a rare genetic disorder that affects the nerves, heart, blood, and brain. Symptoms usually come on slowly and begin in mid-adulthood
  • hereditary elliptocytosis
  • hereditary spherocytosis

Acquired causes of poikilocytosis include:

All newborn babies in the United States are screened for certain genetic blood disorders, like sickle cell anemia. Poikilocytosis may be diagnosed during a test called a blood smear. This test may be done during a routine physical exam, or if you’re experiencing unexplained symptoms.

During a blood smear, a doctor spreads a thin layer of blood on a microscope slide and stains the blood to help differentiate the cells. The doctor then views the blood under a microscope, where the sizes and shapes of the RBCs can be seen.

Not every single RBC will take on an abnormal shape. People with poikilocytosis have normally shaped cells mixed in with abnormally shaped cells. Sometimes, there are several different types of poikilocytes present in the blood. Your doctor will try to figure out which shape is most prevalent.

In addition, your doctor will likely run more tests to find out what’s causing your abnormally shaped RBCs. Your doctor may ask you questions about your medical history. Be sure to tell them about your symptoms or if you’re taking any medications.

Examples of other diagnostic tests include:

There are several different types of poikilocytosis. The type depends on the characteristics of the abnormally shaped RBCs. While it’s possible to have more than one type of poikilocyte present in the blood at any given time, usually one type will outnumber the others.


Spherocytes are small, dense round cells that lack the flattened, lighter-colored center of regularly shaped RBCs. Spherocytes may be seen in the following conditions:

Stomatocytes (mouth cells)

The central part of a stomatocyte cell is elliptical, or slit-like, instead of round. Stomatocytes are often described as mouth-shaped, and may be seen in people with:

Codocytes (target cells)

Codocytes are sometimes called target cells because they often resemble a bullseye. Codocytes may appear in the following conditions:

  • thalassemia
  • cholestatic liver disease
  • hemoglobin C disorders
  • people who recently had their spleen removed (splenectomy)

While not as common, codoctyes may also be seen in people with sickle cell anemia, iron deficiency anemia, or lead poisoning.


Often called wafer cells, leptocytes are thin, flat cells with hemoglobin at the edge of the cell. Leptocytes are seen in people with thalassemia disorders and those with obstructive liver disease.

Sickle cells (drepanocytes)

Sickle cells, or drepanocytes, are elongated, crescent-shaped RBCs. These cells are the characteristic feature of sickle cell anemia as well as hemoglobin S-thalassemia.

Elliptocytes (ovalocytes)

Elliptocytes, also referred to as ovalocytes, are slightly oval to cigar-shaped with blunt ends. Usually, the presence of a large number of elliptocytes signals an inherited condition known as hereditary elliptocytosis. Moderate numbers of elliptocytes may be seen in people with:

Dacryocytes (teardrop cells)

Teardrop erythrocytes, or dacryocytes, are RBCs with one round end and one pointy end. This type of poikilocyte may be seen in people with:

Acanthocytes (spur cells)

Acanthocytes have abnormal thorny projections (called spicules) on the edge of the cell membrane. Acanthocytes are found in conditions such as:

Echinocytes (burr cells)

Like acanthocytes, echinocytes also have projections (spicules) on the edge of the cell membrane. But these projections are typically evenly spaced and occur more frequently than in acanthocytes. Echinocytes are also called burr cells.

Echinocytes might be seen in people with the following conditions:

  • pyruvate kinase deficiency, an inherited metabolic disorder that affects the survival of RBCs
  • kidney disease
  • cancer
  • immediately following a transfusion of aged blood (echinocytes may form during storage of the blood)

Schizocytes (schistocytes)

Schizocytes are fragmented RBCs. They’re commonly seen in people with hemolytic anemias or may appear in response to the following conditions:

  • sepsis
  • severe infection
  • burns
  • tissue injury

The treatment for poikilocytosis depends on what’s causing the condition. For example, poikilocytosis caused by low levels of vitamin B-12, folate, or iron will likely be treated by taking supplements and increasing the amount of these vitamins in your diet. Or, doctors may treat the underlying disease (like celiac disease) that may have caused the deficiency in the first place.

People with inherited forms of anemia, like sickle cell anemia or thalassemia, may require blood transfusions or a bone marrow transplant to treat their condition. People with liver disease may require a transplant, while those with serious infections may need antibiotics.

The long-term outlook for poikilocytosis depends on the cause and how quickly you’re treated. Anemia caused by iron deficiency is treatable and often curable, but it can be dangerous if not treated. This is especially true if you’re pregnant. Anemia during pregnancy can cause pregnancy complications, including serious birth defects (such as neural tube defects).

Anemia caused by a genetic disorder such as sickle cell anemia will require lifelong treatment, but recent medical advancements have improved the outlook for those with certain genetic blood disorders.