What is the significance of an elevated Mean Corpuscular Volume (MCV) of 109.70 in the absence of anemia?

From the Guidelines

An MCV of 109.70 without anemia indicates macrocytosis, which requires investigation into its cause, as it may progress to anemia if left unaddressed, and management should focus on identifying and treating underlying conditions such as vitamin B12 or folate deficiency, liver disease, alcohol use, certain medications, hypothyroidism, or myelodysplastic syndromes 1.

Key Considerations

• Macrocytosis is characterized by larger than normal red blood cells, which can be due to various factors including vitamin deficiencies, liver disease, and certain medications.
• The absence of anemia does not negate the need for investigation, as macrocytosis can be an early sign of an underlying condition that may eventually lead to anemia.
• A comprehensive diagnostic approach should include tests for vitamin B12 and folate levels, liver function, thyroid function, and possibly a peripheral blood smear to identify the cause of macrocytosis.

Diagnostic Approach

• Initial steps should involve assessing the patient's medical history, lifestyle factors (such as alcohol consumption), and current medications to identify potential causes of macrocytosis.
• Laboratory tests should be ordered based on the clinical suspicion of underlying conditions, including vitamin B12 and folate deficiency, which are common causes of macrocytosis 1.
• The presence of inflammation, as indicated by elevated CRP or ESR, may complicate the diagnosis and require a more nuanced approach to differentiate between iron deficiency anemia and anemia of chronic disease 1.

Management

• If a deficiency is identified, supplementation with vitamin B12 (e.g., 1000 mcg daily) or folate (e.g., 1 mg daily) is recommended to address the underlying cause of macrocytosis.
• Lifestyle modifications, such as reducing alcohol consumption, may also be necessary depending on the identified cause.
• Regular follow-up with blood work in 3-6 months is crucial to monitor for changes in the MCV and to assess the effectiveness of the treatment plan.

Underlying Conditions

• Vitamin B12 or folate deficiency: These are common causes of macrocytosis and can be addressed through supplementation.
• Liver disease: May lead to macrocytosis due to impaired liver function affecting vitamin metabolism and red blood cell production.
• Alcohol use: Chronic alcohol consumption can lead to macrocytosis, and reducing or cessation of alcohol use may be necessary.
• Certain medications: Such as those used in chemotherapy or to treat certain autoimmune diseases, can cause macrocytosis as a side effect.
• Hypothyroidism: An underactive thyroid gland can lead to macrocytosis, and treatment of the underlying thyroid condition is necessary.
• Myelodysplastic syndromes: A group of disorders caused by poorly formed or dysfunctional blood cells, which can lead to macrocytosis.

From the Research

Causes of Macrocytosis without Anemia

• Macrocytosis, defined as a mean corpuscular volume (MCV) greater than 100 fL, can occur without anemia, as seen in the given MCV value of 109.70 2, 3, 4.
• The most common causes of macrocytosis without anemia are alcoholism, vitamin B12 and folate deficiencies, and medications 3, 4.
• A study found that 9 cases (20.9%) of Vitamin B12 deficiency presented with isolated macrocytosis without anemia 3.
• Another study suggested that macrocytosis needs to be evaluated even in the absence of anemia, as it may be the first clue to an underlying pathology 3.

Diagnostic Approach

• A complete medical history, red cell parameters, and peripheral blood smear are simple, inexpensive tools that can assist in identifying the underlying cause of macrocytosis 3, 4.
• Vitamin B12 level, reticulocyte count, and a peripheral smear are helpful in delineating the underlying cause of macrocytosis 4.
• When the peripheral smear indicates megaloblastic anemia, vitamin B12 or folate deficiency is the most likely cause 4.
• A serum vitamin B12 determination remains the best test for unmasking vitamin B12 deficiency 5.

Possible Etiologies

• Alcoholism is a common cause of macrocytosis, and patients with macrocytosis should be asked about their alcohol consumption 2, 3, 4.
• Vitamin B12 and folate deficiencies are also common causes of macrocytosis, and serum B12 vitamin should be measured at least when nonanemic macrocytosis is combined with a low red cell count or a high red cell distribution width (E-CDW) and the thrombocyte count and T-MCV are normal 2.
• Other possible etiologies include hypothyroidism, liver disease, and primary bone marrow dysplasias (including myelodysplasia and myeloproliferative disorders) 4, 6.