What is the next step in investigating a 44-year-old female with erythrocytosis (high Red Blood Cell count), elevated hematocrit (Hct), thrombocytosis (high platelet count), normal hemoglobin, iron deficiency (low ferritin), and vitamin B12 deficiency, who is on amlodipine (calcium channel blocker)?

Next Steps in Investigation for a 44-Year-Old Female with Erythrocytosis, Elevated Hematocrit, Thrombocytosis, Normal Hemoglobin, Low Ferritin, and Low B12

The next step in investigation should include a complete workup for iron deficiency and vitamin B12 deficiency, with reticulocyte count, iron studies (including transferrin saturation), and methylmalonic acid levels to confirm the deficiencies and rule out underlying causes. 1

Initial Assessment of the Abnormal Blood Profile

• The patient presents with a complex hematologic picture: high RBC count, high hematocrit, high platelets, normal hemoglobin, low ferritin, and low B12 1
• This combination suggests a mixed nutritional deficiency pattern with potential bone marrow response issues 1
• Abnormalities in multiple cell lines (RBCs and platelets) warrant careful evaluation and may require hematology consultation 1

Iron Deficiency Evaluation

• Complete iron studies should be obtained, including:

  • Serum ferritin (already low, confirming depleted iron stores) 1
  • Transferrin saturation (to assess iron available for erythropoiesis) 1
  • Serum iron levels 1
  • Percent hypochromic red blood cells if available 1

• Low ferritin with normal hemoglobin but high RBC count suggests a compensatory response to iron deficiency 1, 2

• In a 44-year-old female with iron deficiency, gastrointestinal blood loss must be ruled out with stool guaiac testing 1, 2

Vitamin B12 Deficiency Confirmation

• The low B12 level should be further investigated with:
  • Methylmalonic acid (MMA) measurement to confirm true B12 deficiency, especially with borderline B12 levels 3, 4
  • Homocysteine levels as an additional marker of functional B12 deficiency 5
  • Assessment for potential causes of B12 malabsorption including testing for H. pylori and intrinsic factor antibodies 3, 4

Additional Testing

• Reticulocyte count to assess bone marrow response to anemia 1
• Complete blood count with red cell indices to further characterize the anemia pattern 1
• Inflammatory markers (CRP) to assess for inflammation that could affect ferritin interpretation 1
• Kidney function tests to rule out renal causes of erythrocytosis 1

Medication Considerations

• Evaluate the potential impact of amlodipine on the hematologic parameters
• Consider whether other medications that might affect B12 absorption are being used (e.g., metformin, proton pump inhibitors) 3, 4

Potential Diagnostic Pitfalls

• Normal hemoglobin despite high RBC count suggests a compensatory mechanism at work 1
• Iron deficiency typically causes microcytosis, but concurrent B12 deficiency can result in a mixed picture 1, 6
• Ferritin is an acute phase reactant and may be falsely elevated in inflammatory states, potentially masking iron deficiency 1
• Normal B12 levels don't rule out functional B12 deficiency, which is why MMA testing is important 5, 6

Follow-up Plan

• After initial testing, treatment should be initiated for confirmed deficiencies 4, 2
• Repeat complete blood count after 4-8 weeks of treatment to assess response 5
• If no improvement with supplementation or if underlying cause remains unclear, hematology consultation is warranted 1