From the Guidelines
An elevated MCV and MCH with normal RBC count, hemoglobin, and hematocrit typically indicates macrocytosis without anemia, suggesting vitamin B12 or folate deficiency, alcohol use disorder, liver disease, hypothyroidism, or certain medications as potential causes. This pattern is characterized by red blood cells that are larger than normal and contain more hemoglobin per cell, but the overall number of red blood cells and total hemoglobin remain adequate. Common causes of this condition include:
- Vitamin B12 or folate deficiency in early stages (before anemia develops) 1
- Alcohol use disorder
- Liver disease
- Hypothyroidism
- Certain medications (especially anticonvulsants, methotrexate, and some HIV medications)
- Myelodysplastic syndrome This finding warrants further investigation, including:
- Assessment of vitamin B12 and folate levels
- Liver function tests
- Thyroid function tests
- Medication review If alcohol consumption is significant, reducing intake is recommended, as alcohol abuse can lead to macrocytosis 1. The underlying mechanism typically involves impaired DNA synthesis leading to delayed nuclear maturation and larger red blood cells, while hemoglobin synthesis continues normally, resulting in cells that are both larger and contain more hemoglobin individually. In patients with inflammatory bowel disease (IBD), macrocytosis may also be indicative of vitamin B12 or folate deficiency, or thiopurine treatment 1. It is essential to distinguish between iron deficiency anemia and anemia of chronic disease, as treatment approaches differ 1. A comprehensive workup, including complete blood count with MCV, reticulocytes, serum ferritin, transferrin saturation, and CRP, can help identify the underlying cause of macrocytosis 1.
From the Research
Understanding CBC Results
- The provided CBC results show an elevated MCV (Mean Corpuscular Volume) and MCH (Mean Corpuscular Hemoglobin) with normal RBC, hemoglobin, and hematocrit levels.
- Elevated MCV indicates macrocytosis, which is defined as a red blood cell mean corpuscular volume >100 femtoliter (fL) 2.
- Macrocytic anemias are generally classified into megaloblastic or nonmegaloblastic anemia, with megaloblastic anemia being caused by deficiency or impaired utilization of vitamin B12 and/or folate 2, 3.
Possible Causes of Macrocytosis
- Megaloblastic anemia can be caused by vitamin B12 deficiency, folate deficiency, or other factors such as myelodysplastic syndrome (MDS), liver dysfunction, alcoholism, or hypothyroidism 2, 3, 4.
- Nonmegaloblastic macrocytic anemia can be caused by chronic liver dysfunction, hypothyroidism, alcohol use disorder, or myelodysplastic disorders 3.
- Macrocytosis can also result from the release of reticulocytes in the normal physiologic response to acute anemia 3.
Association with Vitamin B12 and Folate Deficiency
- Low vitamin B12 status has been associated with anemia and macrocytosis, with increased risk observed at values below commonly used B12 lower-reference thresholds 5.
- Low folate status has also been associated with anemia and macrocytosis, with similar findings to vitamin B12 deficiency 5.
- In seniors with low vitamin B12 status, high serum folate has been associated with anemia and cognitive impairment, while high serum folate with normal vitamin B12 status may be associated with protection against cognitive impairment 6.