Diagnosis and Management of Mild Macrocytic Anemia with Leukocytosis

Laboratory Interpretation

The hemoglobin of 12.2 g/dL represents mild anemia in an adult male, with normal hemoglobin levels being greater than 13.0 g/dL, according to the American Society of Hematology 3
A mean corpuscular volume (MCV) of 96.2 fL indicates borderline macrocytosis, approaching the threshold of 100 fL that defines true macrocytosis, as suggested by the American College of Physicians 1
This pattern suggests early megaloblastic changes or a mixed picture, as indicated by the European Hematology Association 4

Serum vitamin B12 level should be measured, with deficiency defined as less than 150 pmol/L or less than 203 ng/L, and if borderline, methylmalonic acid greater than 271 nmol/L should be obtained to confirm deficiency, as recommended by the National Institute of Diabetes and Digestive and Kidney Diseases 1, 2
Serum folate and RBC folate levels should be assessed, with deficiency defined as serum folate less than 10 nmol/L or RBC folate less than 305 nmol/L, according to the American College of Medical Genetics 1, 2
Reticulocyte count should be performed to differentiate megaloblastic (low/normal count) from non-megaloblastic causes (elevated count suggests hemolysis or hemorrhage), as suggested by the International Society for Laboratory Hematology 4, 1, 2
TSH and free T4 should be measured to exclude hypothyroidism as a cause of macrocytosis, as recommended by the Endocrine Society 1, 2

If reticulocyte count is low/normal, vitamin B12 deficiency is the most common megaloblastic cause, as indicated by the American Society of Hematology 1
If reticulocyte count is elevated, hemolysis should be considered, with checks for haptoglobin, LDH, and bilirubin, as suggested by the European Hematology Association 4, 1

Never initiate folate supplementation before ruling out and treating vitamin B12 deficiency, as this can precipitate subacute combined degeneration of the spinal cord, an irreversible neurological complication, as warned by the National Institute of Neurological Disorders and Stroke 1, 2
Treatment for vitamin B12 deficiency without neurological symptoms is cyanocobalamin 1 mg IM three times weekly for 2 weeks, then 1 mg every 2-3 months for life, as recommended by the American College of Physicians 1, 2

Repeat complete blood count should be performed to monitor treatment response, with an acceptable response defined as hemoglobin increase of at least 2 g/dL within 4 weeks of treatment, as suggested by the International Society for Laboratory Hematology 1, 2

The mild leukocytosis with immature granulocytes warrants clinical correlation, assessing for fever, infection, or inflammatory conditions that may be contributing to both findings, as indicated by the Infectious Diseases Society of America 4, 1
In patients with inflammatory conditions, ferritin may be falsely elevated despite true iron deficiency, so transferrin saturation and RDW should be checked if inflammation is present, as recommended by the American College of Rheumatology 4, 1, 2