Anisocytosis, a term frequently encountered in blood test results, refers to a condition where a person’s red blood cells are of unequal size. Normally, these oxygen-carrying cells maintain a uniform size. When a blood test indicates “anisocytosis present,” it signifies a noticeable variation in their volume. This finding is not a disease itself, but an observation that can point to underlying changes within the body’s red blood cell production.
What Anisocytosis Means
Anisocytosis describes the presence of red blood cells that differ significantly in size. This variation is measured by the Red Cell Distribution Width (RDW), a component of a complete blood count (CBC). The RDW is a numerical value or percentage that quantifies the variability in red blood cell volumes.
A higher RDW indicates a greater disparity in cell sizes, meaning some red blood cells are much larger or smaller than average. A normal RDW range typically falls between 12% and 15%, though specific laboratory reference ranges can vary slightly. When the RDW is elevated, it suggests that the red blood cell population includes a mix of different sizes, a phenomenon known as anisocytosis. Conversely, a low RDW indicates that red blood cells are uniform in size. Thus, a high RDW is the direct measurement indicating anisocytosis.
Why Anisocytosis Occurs
Anisocytosis is a sign, not a standalone diagnosis, arising from various conditions that disrupt the normal production or maturation of red blood cells. One common cause is iron deficiency anemia, where insufficient iron leads to the production of smaller-than-normal red blood cells. Megaloblastic anemias, often resulting from deficiencies in vitamin B12 or folate, cause the bone marrow to produce abnormally large red blood cells. Both scenarios lead to a mixed population of cell sizes and a high RDW.
Inherited conditions like thalassemia can also cause anisocytosis, resulting in smaller red blood cells. Similarly, sickle cell disease, a genetic disorder, produces abnormally shaped red blood cells that vary in size. Beyond anemias, other medical issues such as liver disease, kidney disease, and certain myelodysplastic syndromes can affect red blood cell development, contributing to size variation. Anisocytosis can also appear during pregnancy due to increased iron requirements, potentially signaling early iron deficiency.
Its Role in Diagnosis
An elevated RDW serves as an important clue for healthcare providers in diagnosing various conditions. It prompts further investigation into the underlying cause of red blood cell size variation. Anisocytosis helps differentiate between types of anemia when considered alongside other blood parameters, such as the Mean Corpuscular Volume (MCV), which measures the average size of red blood cells.
A high RDW combined with a low MCV might suggest iron deficiency anemia or thalassemia, while a high RDW with a high MCV could indicate vitamin B12 or folate deficiency. This allows medical professionals to narrow down possibilities and guide subsequent diagnostic tests. While not a definitive diagnosis, its presence helps to piece together a comprehensive picture of a patient’s blood health, directing the path toward identifying and addressing the root medical issue.