Burr cells, also known as echinocytes, are abnormally shaped red blood cells observed in a blood sample. Their presence is a non-specific indicator that can point towards various underlying medical conditions, signaling that further investigation is warranted.
Understanding Burr Cells
Burr cells have a distinctive appearance under a microscope. They are red blood cells characterized by 10 to 30 uniform, short, blunt projections or spicules distributed evenly around their surface. This gives them a serrated or “sea urchin-like” look. These cells typically retain their central pallor, the lighter area in the center of a red blood cell. Their identification usually occurs through examination of a peripheral blood smear.
How Burr Cells Form
The formation of burr cells arises from changes that disrupt the normal biconcave disc shape of red blood cells. These changes often involve alterations in the red blood cell membrane, specifically its lipid composition or the balance of lipids within the membrane. An imbalance in plasma electrolytes or altered cellular metabolism, particularly a decrease in adenosine triphosphate (ATP) levels, can also contribute to their formation. The presence of certain toxins or metabolic waste products in the blood can induce these membrane changes, causing the cell to buckle outward in multiple locations and form the characteristic spiky projections.
Conditions Associated with Burr Cells
Burr cells are commonly found in several medical conditions, each affecting red blood cell integrity in different ways. Kidney disease, especially chronic kidney disease and uremia, is a frequent association. In these cases, the accumulation of metabolic waste products and toxins, which the kidneys normally filter, affects the red blood cell membrane, leading to burr cell formation.
Liver disease can also lead to the presence of burr cells, often due to altered lipid metabolism or the accumulation of abnormal lipoproteins that impact the red blood cell membrane. Hypophosphatemia, a low level of phosphate in the blood, can also induce burr cell formation as phosphate plays a role in red blood cell energy metabolism and membrane stability.
Microangiopathic hemolytic anemias (MAHA), such as disseminated intravascular coagulation (DIC), thrombotic thrombocytopenic purpura (TTP), and hemolytic uremic syndrome (HUS), are conditions where burr cells can appear. In MAHA, red blood cells suffer mechanical damage as they pass through narrowed or obstructed small blood vessels, leading to fragmentation and altered shapes, including burr cells.
Severe burns can also result in burr cell formation, possibly due to changes in plasma lipids and proteins that interact with the red blood cell membrane. Certain cancers, including gastric carcinoma and other disseminated malignancies, have also been noted to sometimes present with burr cells, though this is less common than with kidney or liver issues.
Clinical Significance of Burr Cell Presence
The identification of burr cells on a blood smear holds clinical significance. Finding burr cells prompts further investigation to identify the underlying medical condition responsible for their formation. This often involves additional diagnostic testing, such as blood chemistry panels to assess kidney and liver function, or more specialized tests depending on the suspected cause. Monitoring the presence and quantity of burr cells can also help in assessing disease progression or the effectiveness of treatment for the underlying condition.