What is the management approach for an adult patient with a low Mean Corpuscular Hemoglobin (MCH) level, indicating possible anemia or iron deficiency?

Management of Low MCH (32.1 pg)

Confirm iron deficiency with serum ferritin before proceeding with any investigation or treatment, as MCH alone is suggestive but not diagnostic of iron deficiency. 1, 2

Initial Diagnostic Workup

Your patient's MCH of 32.1 pg is actually within the normal range (27-33 pg), so this does not indicate hypochromia or iron deficiency. However, if you suspect iron deficiency based on other clinical factors, proceed as follows:

Essential Laboratory Tests

• Serum ferritin is the single most useful marker and must be obtained to confirm iron deficiency before investigation 1, 2

  • <15 μg/L is highly specific (99%) for iron deficiency 2
  • <30 μg/L indicates depleted iron stores 2
  • <45 μg/L suggests deficiency even with mild inflammation 2

  • 150 μg/L makes absolute iron deficiency unlikely 2

• Complete blood count including hemoglobin, MCV, and RDW to assess for anemia and evaluate bone marrow function 1, 3

  • Anemia is defined as Hb <130 g/L in men or <120 g/L in non-pregnant women over age 15 1, 2

• Transferrin saturation can be helpful if false-normal ferritin is suspected due to inflammation 1

Additional Testing When Indicated

• Hemoglobin electrophoresis should be obtained if microcytosis is present with normal iron studies to exclude thalassemia, particularly in patients of appropriate ethnic background 2

• Vitamin B12 and folate levels are essential if macrocytosis is present, as combined deficiencies can mask the typical microcytic picture of iron deficiency 4

• CRP or inflammatory markers should be assessed if inflammation may be affecting ferritin interpretation 4

Treatment Approach Based on Findings

If Iron Deficiency is Confirmed

• Oral iron therapy with ferrous sulfate 325 mg daily (containing 65 mg elemental iron) is first-line treatment 4, 5

• Monitor response: Expect hemoglobin rise ≥10 g/L within 2 weeks if iron deficiency is the cause 1, 4

  • A good response to iron therapy is highly suggestive of absolute iron deficiency, even if initial iron studies were equivocal 1, 2

Investigation for Underlying Cause

• Consider investigation at any level of anemia in the presence of confirmed iron deficiency, though the case is stronger with more severe degrees of anemia 1, 2

• Fast-track GI referral is warranted for Hb <110 g/L in men or <100 g/L in non-menstruating women, though these cut-offs may miss some cases of colorectal cancer, especially in men 1

• For non-anemic iron deficiency (if female patient with normal Hb), GI investigation is generally not warranted in premenopausal women but should be considered in men, postmenopausal women, or those with GI symptoms or family history of GI pathology 2

Common Pitfalls to Avoid

• Do not assume microcytosis must be present with iron deficiency, as coexisting macrocytic causes (B12/folate deficiency) can mask the typical microcytic picture 4

• Do not rely on MCH or MCV alone for diagnosis—while MCH has high sensitivity (97-100%) for identifying iron deficiency, it has moderate accuracy (ROC 0.67-0.72) and requires ferritin confirmation 2, 6

• Do not assume normal ferritin excludes iron deficiency in inflammatory states, as ferritin up to 45-100 μg/L may still represent iron deficiency with inflammation 2, 4

• Do not treat with folate before excluding B12 deficiency if macrocytosis is present, as this can cause irreversible neurological damage 4

• Assess compliance and absorption if iron deficiency persists despite adequate oral supplementation, as malabsorption is rare but possible, particularly in prolonged iron deficiency 7