Macrocytosis

Last updated Nov. 2, 2025, 8:10 a.m. by ivo

Tags: Macrocytosis

Macrocytosis Macrocytosis refers to an increased red cell mean cell volume (MCV). The normal MCV will vary depending on the age of the patient, but in adults, is generally considered increased when it is > 100 fL. Macrocytosis is a common abnormality that is not pathological per se.

Causes

• B12 or folate deficiency.
• An isolated macrocytosis due to alcohol consumption is common
• Liver disease
• Medications (e.g., hydroxyurea, azathioprine, methotrexate). .
• Cigarette smoking has also been implicated.
• Hypothyroidism.
• An isolated macrocytosis may be an early feature of myelodysplastic syndrome.

Further evaluation

• B12 and folate studies
• Thyroid function tests
• Liver function tests
• Correlation with medication and alcohol history
• Making a diagnosis of Myelodysplastic Syndrome is difficult in the absence of cytopenias (i.e. Hb < 100 g/L, platelet count < 100 x 10⁹/L, neutrophils < 1 x 10⁹/L), and there is no treatment available to delay the progression of early Myelodysplastic Syndrome. As such, a watch and wait approach with 6-12 monthly FBCs is appropriate.

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When To Refer

• Anaemia (Hb <100 g/L)
• Thrombocytopenia (platelet count <100 x 10⁹/L)
• Neutropenia (neutrophil count <1 x 10⁹/L)
• Persistent monocytosis
• Left shift or immature cells (blasts or nucleated red cells) on peripheral blood
• Dysplastic changes on the blood film