RDW (Red Cell Distribution Width)

The Red Cell Distribution Width (RDW) is a parameter reported in complete blood count (CBC) tests, which measures the variation in size of red blood cells (erythrocytes) in the blood.

What does RDW measure?

RDW measures the range of red blood cell sizes, reported as a percentage or femtoliters (fL). It calculates the distribution of red blood cell volumes, providing insight into the uniformity of red blood cell size. A normal RDW indicates that red blood cells are relatively uniform in size, while an elevated RDW suggests a larger variation in red blood cell sizes.

Normal RDW values

The normal range for RDW is typically between 11.5% and 14.5%. However, this range may vary slightly depending on the laboratory or the specific analyzer used to perform the test.

Elevated RDW values

An elevated RDW can be indicative of several conditions, including:

• Anisocytosis: a condition characterized by an uneven distribution of red blood cell sizes.
• Iron deficiency anemia: a lack of iron in the body, which can lead to the production of abnormally small or large red blood cells.
• Vitamin B12 or folate deficiency: deficiencies in these essential nutrients can affect red blood cell production and size.
• Anemia of chronic disease: a condition where anemia occurs in response to chronic diseases, such as rheumatoid arthritis or cancer.
• Myeloproliferative disorders: conditions characterized by the overproduction of blood cells, including red blood cells.

Decreased RDW values

A decreased RDW is less common and may be seen in conditions such as:

• Hereditary spherocytosis: a genetic disorder characterized by the production of abnormally small, sphere-shaped red blood cells.
• Other rare red blood cell disorders.

Clinical significance of RDW

The RDW is an important parameter in the diagnosis and monitoring of various conditions affecting red blood cells. It can help healthcare providers:

• Differentiate between different types of anemia.
• Monitor response to treatment for conditions such as iron deficiency anemia or vitamin B12 deficiency.
• Identify potential underlying conditions that may be contributing to anemia or other red blood cell disorders.

Limitations and considerations

While the RDW is a valuable parameter, it should be interpreted in conjunction with other laboratory results and clinical findings. Factors such as sample quality, instrument calibration, and individual variability can affect RDW results.