Macrocytosis is a condition where red blood cells are larger than normal. These enlarged cells, also known as macrocytes, are defined by a mean corpuscular volume (MCV) that exceeds the upper reference range established by the laboratory and hematology analyzer (usually >110 fL). Upon examination of a peripheral blood smear under microscope, these macrocytes appear larger than standard erythrocytes. It’s noteworthy that macrocytosis is a common morphological feature in neonatal peripheral blood. The presence of macrocytosis can indicate a range of conditions, from benign, treatable illnesses to more serious underlying disorders.

Types

Macrocytes may be oval or round. Oval macrocytes (also called megalocytes) are seen in conditions associated with dyserythropoiesis including megalobalstic anemia, myelodysplstic syndromes, Fanconi anemia and CDA type I & III. Round macrocytes are associated with other causes of macrocytosis.

Causes

In humans, the most prevalent causes of macrocytosis are often linked to alcoholism and deficiencies in vitamin B12 or folic acid (Vitamin B9), or a combination of these factors. These conditions can affect the production and development of red blood cells, leading to their enlargement. Another cause of macrocytosis is benign familial macrocytosis, which is a hereditary condition that doesn’t present any symptoms. Despite the larger size of the red blood cells, individuals with this condition typically have normal red blood cell function. It’s always important to consult with a healthcare professional for accurate diagnosis and treatment. Causes of Macrocytosis may include:

Complications

No complications arise from macrocytosis itself and a prognosis will be determined from its cause.