Red blood cells (RBCs) are disc-shaped cells responsible for transporting oxygen throughout the body. When these cells undergo a change in their environment, they can transform into a shrunken, spiky, or scalloped appearance, known as crenated red blood cells. This change in shape can signal various underlying conditions or simply be a result of how the blood sample was handled.
What Are Crenated Red Blood Cells?
Crenated red blood cells exhibit numerous spiky or scalloped projections extending from their surface. These projections give the cells a “burr-like” or “thorny” look. This change in appearance is a direct result of the cell losing water.
The biconcave disc shape of a healthy red blood cell is maintained by a delicate balance of water inside and outside the cell. When this balance is disrupted, water moves out of the cell, causing it to shrink. As the cell volume decreases, its membrane folds and puckers, forming the characteristic spiky projections.
Common Causes of Crenation
Red blood cells can become crenated for reasons related to their surrounding environment or how a blood sample is prepared. A common physiological cause is exposure to a hypertonic environment, where the concentration of solutes outside the cell is higher than inside. In such conditions, water moves out of the red blood cell through osmosis to equalize solute concentration, leading to cell shrinkage.
This hypertonic state can arise from conditions like severe dehydration, where the body’s fluid levels are low, or from electrolyte imbalances, particularly high sodium levels (hypernatremia) or high blood sugar (hyperglycemia). Certain medical interventions, such as administering hypertonic intravenous solutions like 3% saline or mannitol, can also draw water out of red blood cells, causing them to crenate.
Crenation can also occur as an artifact during blood sample collection and preparation. Improper handling, such as slow drying of a blood smear on a slide, can cause red blood cells to lose water and crenate before examination. Prolonged storage of blood samples, especially if stored improperly or with certain anticoagulants like EDTA, can also lead to artificial crenation.
Types of Crenated Red Blood Cells and Associated Conditions
Crenated red blood cells are broadly categorized into two main types based on the appearance of their projections: echinocytes and acanthocytes. Differentiating these forms is important as they are associated with different underlying conditions.
Echinocytes, often called “burr cells,” are characterized by numerous small, uniform, and regularly spaced projections across their entire surface. While they can be an artifact of sample handling, they are also observed in certain medical conditions. These include kidney dysfunction (uremia), severe dehydration, gastrointestinal bleeding, and stomach carcinoma.
Acanthocytes, also known as “spur cells,” display fewer, larger, and irregularly distributed spicules. These cells indicate more serious underlying medical conditions compared to echinocytes. They are associated with severe liver disease, such as cirrhosis, where alterations in the red blood cell membrane’s lipid content occur. Acanthocytes can also be a feature of certain neurological disorders, some forms of hemolytic anemia, malnutrition, hypothyroidism, and post-spleen removal (splenectomy).
When Are Crenated RBCs a Concern?
The detection of crenated red blood cells occurs through microscopic examination of a peripheral blood smear. A small sample of blood is spread thinly on a glass slide, stained, and then viewed under a microscope to assess the shape and appearance of red blood cells.
Interpreting the presence of crenated red blood cells requires determining if the crenation is an artifact from sample handling or if it signifies an underlying health issue. A fresh blood sample is preferable for accurate diagnosis, as delayed preparation can induce crenation.
If crenation is determined to be pathological rather than an artifact, further medical evaluation is necessary. This evaluation may involve additional blood tests to check electrolyte levels, kidney function, or liver function, along with a thorough review of the patient’s medical history and a physical examination. Treatment for pathological crenation involves addressing the underlying medical condition causing the change in red blood cell shape, rather than directly treating the crenation itself. For instance, correcting dehydration or managing kidney disease can lead to the resolution of crenated red blood cells.