What is the appropriate management for a patient with iron deficiency anemia and persistent lymphocytosis, suggestive of a monoclonal disorder, in the context of borderline microcytosis and normal hemoglobin levels?

Management of Iron Deficiency with Persistent Lymphocytosis

Immediate Priority: Address Both the Iron Deficiency and Investigate the Lymphocytosis

You must initiate oral iron supplementation immediately while simultaneously pursuing urgent investigation of the persistent lymphocytosis with flow cytometry, as the laboratory comment explicitly suggests a monoclonal disorder that requires hematologic evaluation. 1

Iron Deficiency Management

Diagnostic Confirmation

• Your ferritin of 20 μg/L confirms iron deficiency (diagnostic threshold <30 μg/L without inflammation), and the borderline MCV of 81 fL with hypochromic cells and low MCH (25.0 pg) further supports this diagnosis 1, 2
• The RDW of 14% at the upper limit of normal is consistent with early iron deficiency 3

Treatment Protocol

• Start ferrous sulfate 200 mg three times daily immediately 1, 4
• Alternative formulations (ferrous gluconate or ferrous fumarate) can be used if ferrous sulfate is not tolerated 1
• Add ascorbic acid to enhance iron absorption if response is suboptimal 1
• Continue iron therapy for 3 months after hemoglobin normalization to replenish iron stores 1

Expected Response

• Hemoglobin should rise ≥10 g/L within 2 weeks if iron deficiency is the primary cause 2
• Failure to respond warrants consideration of malabsorption, ongoing blood loss, or non-compliance 2

Investigation of Iron Loss Source

• Despite normal hemoglobin (137 g/L), you must investigate the source of iron deficiency 1, 2
• Gastrointestinal evaluation is mandatory: upper endoscopy and colonoscopy to exclude occult GI malignancy, particularly given the laboratory's specific mention of "GI causes" 1
• Screen for celiac disease with tissue transglutaminase antibodies, as malabsorption is a common cause 1, 2
• Review for NSAID use and obtain detailed dietary history, though positive findings should not preclude full GI investigation 1

Monitoring

• Recheck hemoglobin and MCV at 3-month intervals for one year, then annually 1
• Repeat ferritin if hemoglobin or MCV falls below normal 1

Lymphocytosis Investigation - URGENT

Immediate Action Required

• Order lymphocyte flow cytometry on peripheral blood immediately, as specifically recommended by the laboratory comment suggesting a monoclonal disorder 1
• Your absolute lymphocyte count of 5.7 × 10^9/L (reference range 1.0-4.0) represents persistent lymphocytosis that requires hematologic evaluation

Differential Considerations

• The combination of lymphocytosis with slight rouleaux formation raises concern for:
  • Chronic lymphocytic leukemia (CLL)
  • Monoclonal B-cell lymphocytosis (MBL)
  • Other lymphoproliferative disorders
• Flow cytometry will identify clonal B-cell populations and characterize cell surface markers 1

Hematology Referral

• Refer to hematology if flow cytometry demonstrates monoclonal lymphocytosis 1
• Even if flow cytometry is negative, persistent unexplained lymphocytosis warrants hematology consultation

Critical Pitfalls to Avoid

• Do not attribute iron deficiency solely to dietary causes without full GI investigation - occult GI malignancy must be excluded 1, 2
• Do not delay lymphocyte flow cytometry - the laboratory has specifically flagged this as requiring follow-up investigation 1
• Do not assume normal hemoglobin excludes significant pathology - borderline microcytosis with low ferritin indicates depleted iron stores requiring investigation 1, 2
• Do not stop iron therapy prematurely - continue for 3 months after correction to replenish stores 1
• Do not overlook the possibility of combined pathology - iron deficiency may coexist with an underlying hematologic disorder 1

Follow-Up Timeline

• Week 2: Assess hemoglobin response to iron therapy 2
• Week 2-4: Complete flow cytometry and GI investigations 1
• Month 3: Recheck CBC, ferritin, and assess need for continued iron supplementation 1
• Months 3,6,9,12: Monitor hemoglobin and MCV 1
• Year 2: Final follow-up assessment 1