In a 57-year-old woman with normal hemoglobin and hematocrit, low mean corpuscular hemoglobin concentration, elevated platelet count (thrombocytosis), and normal iron studies, what is the likely cause and how should she be managed?

Management of Low MCHC with Thrombocytosis and Normal Iron Studies

Despite normal iron studies, this 57-year-old woman requires iron supplementation and close monitoring, as the combination of low MCHC (30.1) and reactive thrombocytosis (571) strongly suggests functional iron deficiency that standard iron panels may not fully capture. 1

Immediate Diagnostic Steps

Obtain complete iron studies including serum ferritin and transferrin saturation (TSAT) if not already done. 1 The most critical values to assess are:

• Ferritin <30 μg/L confirms iron deficiency in the absence of inflammation; <15 μg/L is diagnostic 1
• TSAT <15-20% supports iron deficiency and is less affected by inflammation than ferritin alone 1
• Reticulocyte count to evaluate bone marrow response—a low or normal count indicates impaired red cell production 1

Low MCHC (hypochromia) is a more reliable marker of iron deficiency than MCV because it is less dependent on storage conditions and reflects both absolute and functional iron deficiency. 2 Your patient's MCHC of 30.1 indicates hypochromic red cells even when hemoglobin appears "normal."

Understanding the Thrombocytosis

Reactive thrombocytosis commonly accompanies iron deficiency anemia and typically resolves with iron repletion. 1 The platelet count of 571 is consistent with this pattern and does not require immediate hematology referral unless it persists after iron correction. 1

However, persistent thrombocytosis after iron correction would require hematology evaluation for primary myeloproliferative disorders. 1

Critical Menstrual Assessment

A detailed menstrual history is essential, including duration of menses, frequency of pad/tampon changes, and passage of clots larger than a quarter. 1 Heavy menstrual bleeding is the most common cause of iron deficiency in premenopausal women (though your patient at 57 may be perimenopausal). 1

Rule Out Thalassemia Trait

If hemoglobin <11.5 g/dL in suspected thalassemia minor, screen for coexisting iron deficiency simultaneously (sensitivity 79.8%, specificity 82.6%). 3 While your patient's hemoglobin is 12.3 g/dL, the low MCHC with normal MCV warrants consideration of:

• Hemoglobin electrophoresis to exclude thalassemia trait, particularly if there is appropriate ethnic background 2
• Thalassemia minor patients commonly have coexisting iron deficiency (31% in one series) 3

Treatment Algorithm

Initiate Iron Supplementation

Start ferrous sulfate 325 mg (65 mg elemental iron) once to three times daily between meals. 1 Lower doses may be better tolerated and should be considered if gastrointestinal side effects occur. 2

• Expect hemoglobin increase of 1-2 g/dL every 2-4 weeks 1
• Continue iron for 3-6 months after hemoglobin normalizes to replenish stores 1
• Oral iron should be continued for 3 months after iron deficiency correction to replenish stores 2

Monitoring Schedule

Recheck CBC after 3 months of iron therapy. 1 Monitor for:

• Hemoglobin and MCHC normalization
• Resolution of thrombocytosis (should decrease as iron stores replete)
• Improvement in reticulocyte response if initially low

When to Refer to Hematology

Refer to hematology if iron studies are normal or thrombocytosis persists after iron correction. 1 Specifically:

• Platelet count >400 × 10³/μL persisting after 3-6 months of iron repletion 1
• No improvement in MCHC despite adequate iron supplementation
• Development of other cytopenias or concerning symptoms

Common Pitfalls to Avoid

Ferritin is an acute phase protein—apparently normal levels may occur with iron deficiency in the context of inflammatory disease. 2 An SF cut-off of 45 μg/L provides optimal trade-off between sensitivity (0.92 specificity) for iron deficiency in practice. 2

Do not assume normal iron studies exclude functional iron deficiency when MCHC is low and thrombocytosis is present. 1 The combination strongly suggests iron-restricted erythropoiesis that warrants empiric iron supplementation.

Avoid unnecessary gastrointestinal investigation at this stage unless iron supplementation fails or there are concerning symptoms (weight loss, change in bowel habits, occult blood). 2 At age 57 with normal hemoglobin, the threshold for invasive testing should be higher than in frank anemia.