Red blood cells, also known as erythrocytes, are microscopic, disc-shaped cells that deliver oxygen throughout the body. Their unique biconcave shape allows flexibility, enabling them to navigate narrow blood vessels and efficiently exchange gases. Maintaining this shape is important for proper function, as deviations can impact their duties.
What Are Burr Cells?
Burr cells, scientifically termed echinocytes, are a type of red blood cell characterized by an abnormal surface. These cells feature multiple small, evenly spaced projections or spikes emanating from their membrane, giving them a “hedgehog” or “sea urchin” appearance. Unlike some other irregularly shaped red blood cells, the projections on burr cells are typically uniform in size and distribution across the cell’s surface. They generally maintain a similar size to normal red blood cells and often retain their central pallor when viewed under a microscope.
How Burr Cells Form
The formation of burr cells involves changes at the cellular membrane level. These alterations often stem from modifications in the red blood cell’s lipid content or imbalances in osmotic pressure. An expansion of the outer layer of the cell membrane relative to the inner layer can drive the outward curving that creates the characteristic spikes. Extrinsic factors, such as high levels of certain fatty acids, or intrinsic factors like a decrease in adenosine triphosphate (ATP) within the cell, can induce this transformation.
A reduction in ATP levels, which can occur during red blood cell aging or storage, is associated with the development of echinocytes. ATP depletion may affect systems maintaining cell membrane lipid balance. While some externally induced burr cell formations can be reversed by placing the cells in fresh plasma, those caused by intrinsic factors are not reversible.
Underlying Medical Conditions
The presence of burr cells can indicate various underlying medical conditions, often signaling systemic issues affecting red blood cell integrity. Kidney disease, including end-stage renal disease or uremia, is a common association, where accumulated waste products in the blood can alter red blood cell morphology. These uremic toxins can lead to changes in the cell membrane structure and function. The appearance of burr cells in such cases may resolve when the metabolic abnormalities of uremia are corrected.
Liver disease, such as cirrhosis, is another cause, as it can alter plasma lipids, affecting the red blood cell membrane. Abnormal high-density lipoproteins can bind to red blood cell surfaces and induce these shape changes. Severe dehydration can also contribute to burr cell formation due to shifts in fluid balance and osmotic conditions affecting red blood cells.
Certain cancers, such as stomach carcinoma, and severe burns are linked to the development of burr cells. In severely burned patients, decreased plasma lipoproteins and echinocyte development may occur together. Some medications, including aspirin, heparin, and certain chemotherapeutic agents, can induce burr cell formation. Pyruvate kinase deficiency, a genetic disorder affecting red blood cell metabolism, can also result in burr cells due to decreased ATP generation and subsequent changes in cell water and potassium content.
Distinguishing True Burr Cells from Artifacts
Observing burr cells in a blood sample does not always signify an underlying medical condition; they can also be an artifact of sample preparation. Factors related to how a blood smear is made or handled can induce these changes. Slow drying of the blood smear, prolonged storage of the blood sample, or the use of improper anticoagulants can lead to artifactual burr cell formation.
Glass slides can release substances that promote echinocyte formation. Changes in the pH or tonicity of staining solutions can also cause red blood cells to crenate and appear as burr cells. Laboratory professionals differentiate true pathological burr cells from artifacts by examining the uniformity of their distribution on the slide and observing other cells in the sample. Understanding these potential artifacts is important for accurate diagnosis and avoiding misinterpretation of blood smear findings.