Low MCH and MCHC with Hemoglobin 12.8 g/dL
Low MCH and low MCHC are suggestive but not diagnostic of iron deficiency, and you must confirm with serum ferritin before making a definitive diagnosis, even with a hemoglobin of 12.8 g/dL. 1
Understanding the Clinical Picture
Your patient has a hemoglobin of 12.8 g/dL, which may or may not represent anemia depending on sex and population:
- In men over 15 years: This is anemia (WHO defines anemia as Hb <130 g/L) 1
- In non-pregnant women over 15 years: This is NOT anemia (WHO defines anemia as Hb <120 g/L) 1
This distinction matters because you may be dealing with non-anemic iron deficiency (NAID) if the patient is female, which still requires investigation in certain populations 1.
Why MCH and MCHC Alone Are Insufficient
The specificity of MCH and MCHC for iron deficiency is limited because these parameters also occur in:
- Thalassemia and other hemoglobinopathies (where MCV is typically reduced out of proportion to anemia) 1
- Sideroblastic anemia 1
- Anemia of chronic disease 1
While MCH is probably a more reliable marker than MCV and may be more sensitive for iron deficiency 1, both microcytosis and hypochromia lose sensitivity in the presence of chronic disease, thalassemia, or vitamin B12/folate deficiency 1.
Required Diagnostic Approach
You must obtain serum ferritin to confirm iron deficiency before proceeding with investigation or treatment 1:
Ferritin Interpretation:
- <15 μg/L: Highly specific for iron deficiency (specificity 0.99) 1
- <30 μg/L: Generally indicative of low body iron stores 1
- <45 μg/L: Optimal trade-off between sensitivity and specificity (specificity 0.92), especially in chronic inflammatory conditions 1
- >150 μg/L: Unlikely to be absolute iron deficiency, even with inflammation 1
Important Caveat:
Ferritin is an acute phase protein, so apparently normal levels may occur with iron deficiency in the context of inflammatory disease 1. If you suspect false-normal ferritin, consider transferrin saturation or other iron parameters 1.
Additional Testing to Consider
If microcytosis is present with normal iron studies, obtain hemoglobin electrophoresis to exclude thalassemia, particularly in patients with appropriate ethnic background 1.
Diagnostic Performance Data
Recent research shows that among red cell parameters for diagnosing iron deficiency 2, 3:
- MCH has moderate accuracy (ROC curve 0.67-0.72) and high sensitivity (97-100% of iron-deficient anemic individuals identified) 2, 4
- MCHC has moderate accuracy (ROC curve 0.71) but was not significant as a predictor in some studies 2, 3
- MCV alone is less reliable than MCH 1
However, 25-39% of normal, non-anemic individuals may have low ferritin, making it less useful as a standalone screening test despite its specificity when truly low 4.
Clinical Action Based on Findings
If ferritin confirms iron deficiency, investigation should be considered at any level of anemia, though the case is stronger with more severe degrees as they are more likely to have serious underlying GI pathology 1.
For non-anemic iron deficiency (if patient is female with Hb 12.8 g/dL):
- GI investigation generally not warranted in premenopausal women (likely menstrual blood loss) 1
- Low threshold for investigation in men, postmenopausal women, or those with GI symptoms or family history of GI pathology 1
A therapeutic trial can be diagnostic: A good response to iron therapy (Hb rise ≥10 g/L within 2 weeks) is highly suggestive of absolute iron deficiency, even if iron studies are equivocal 1.