Mild Macrocytosis with Normal MCH in an Elderly Male
An MCV of 100.6 fL with MCH of 34.2 pg/dL in an elderly male indicates mild macrocytosis that requires systematic evaluation for vitamin B12/folate deficiency, medication effects, early myelodysplastic syndrome, and occult blood loss, even though the values are only marginally elevated. 1
Understanding These Values
- MCV of 100.6 fL is just above the upper limit of normal (100 fL), placing this patient in the macrocytic category, though only mildly elevated 2
- MCH of 34.2 pg is within normal range (normal ~27-33 pg), which is actually slightly elevated and typically accompanies macrocytosis 3
- The combination of borderline elevated MCV with normal-to-high MCH narrows the differential to macrocytic processes without concurrent iron deficiency 1
Critical First Steps
Order these essential tests immediately:
- Reticulocyte count to distinguish between ineffective erythropoiesis (low/normal) versus hemolysis or recent blood loss (elevated) 1, 4
- Serum vitamin B12 and folate levels are mandatory, as deficiency remains the most common cause even with mild MCV elevation 1, 5
- Peripheral blood smear to look for hypersegmented neutrophils (B12/folate deficiency), schistocytes (hemolysis), or dysplastic changes (myelodysplastic syndrome) 1, 3
- Complete iron studies (ferritin, transferrin saturation) because mixed deficiencies can mask each other—a normal MCH does NOT exclude concurrent iron deficiency 1
Most Likely Causes in Elderly Males
Vitamin B12 or folate deficiency remains possible even at MCV 100.6, particularly in elderly patients with malabsorption or dietary insufficiency 1, 5
Medication-induced macrocytosis should be strongly considered if the patient takes:
- Hydroxyurea, methotrexate, azathioprine, or other chemotherapeutic agents 2, 1
- Anticonvulsants like diphenytoin 2
- Antiretroviral medications 1
Early myelodysplastic syndrome (MDS) must be considered in elderly patients, though MDS typically presents with other cytopenias or more severe macrocytosis 1
Chronic alcohol use causes macrocytosis independent of nutritional deficiencies 3
Critical Pitfall to Avoid
Do not assume normal B12/folate levels exclude deficiency. If initial B12 and folate are normal but no other cause is identified, check methylmalonic acid (MMA) and homocysteine to detect tissue-level deficiency despite normal serum levels 1, 4
Mixed deficiency states are common in elderly patients. Concurrent iron deficiency with B12/folate deficiency can result in a falsely normal MCV, but will show elevated red cell distribution width (RDW) 1, 3
If Initial Workup Shows Normal B12/Folate
Review all medications thoroughly, as many drugs cause macrocytosis through myelosuppressive activity rather than vitamin deficiency 4
Check for hemolysis if reticulocyte count is elevated: obtain haptoglobin, LDH, and indirect bilirubin 4
Consider occult gastrointestinal blood loss, particularly in elderly males—endoscopy may be warranted to evaluate for malignancy if iron deficiency is also present 6
Monitoring Strategy
Even if no cause is identified, ongoing monitoring is essential because a significant percentage of patients with unexplained macrocytosis develop primary bone marrow disorders or worsening cytopenias over time 1
Repeat CBC every 3-6 months and reassess B12/folate levels periodically, as deficiencies may develop later 1
Consider hematology consultation if the cause remains unclear after initial workup, if MCV continues to rise, or if other cytopenias develop 4
Special Considerations for Elderly Patients
Anemia should never be regarded as normal aging. In elderly males, the combination of mild macrocytosis warrants thorough investigation for underlying malignancy, chronic kidney disease, or myelodysplastic syndrome 7, 6
Sensitivity of MCV for B12 deficiency is only 30-77% depending on the population studied, meaning many B12-deficient patients will have normal or only mildly elevated MCV 8, 9
In elderly patients with inflammatory conditions, serum ferritin up to 100 μg/L may still be consistent with iron deficiency, making comprehensive iron studies particularly important 2, 4