Low MCHC (31.9 g/dL): Diagnostic Approach and Management
A low MCHC of 31.9 g/dL indicates hypochromic anemia, most commonly caused by iron deficiency, and requires evaluation with complete blood count indices, iron studies, and targeted iron replacement therapy. 1
What Low MCHC Indicates
Low MCHC reflects reduced hemoglobin concentration within red blood cells (hypochromia), typically indicating iron deficiency anemia when accompanied by microcytosis. 2
MCHC should be interpreted alongside MCV (mean corpuscular volume), MCH (mean corpuscular hemoglobin), and RDW (red cell distribution width) for accurate diagnosis. 2, 1
Iron deficiency anemia characteristically presents with low MCV, low MCH, low MCHC, and elevated RDW (>14%), distinguishing it from thalassemia minor which shows low MCV but normal RDW. 2
In inflammatory bowel disease and chronic inflammatory conditions, microcytic hypochromic anemia (low MCHC) can result from either true iron deficiency or anemia of chronic disease. 2
Required Diagnostic Workup
The minimum workup must include: 2, 1
- Complete blood count with red cell indices (MCV, MCH, MCHC, RDW)
- Reticulocyte count to assess bone marrow response
- Serum ferritin to evaluate iron stores
- Transferrin saturation (TfS) to assess iron availability for erythropoiesis
- C-reactive protein (CRP) to detect inflammation
Diagnostic criteria for iron deficiency depend on inflammatory status: 2
- Without inflammation: serum ferritin <30 μg/L confirms iron deficiency 2
- With inflammation present: serum ferritin up to 100 μg/L may still indicate iron deficiency 2
- Transferrin saturation <16-20% supports iron-restricted erythropoiesis 2
Treatment Approach
Iron Supplementation
Iron replacement is the primary treatment for iron deficiency causing low MCHC: 1
- Initiate oral or intravenous iron supplementation based on severity and tolerance
- Expect hemoglobin improvement within 2-4 weeks of starting iron therapy 1
- Continue iron supplementation for 3-6 months after hemoglobin normalization to replenish iron stores 1
- Recheck CBC and iron studies after 4-8 weeks to assess treatment response 1
When to Consider Alternative Diagnoses
If no improvement occurs despite adequate iron supplementation, consider: 1
- Anemia of chronic disease (ferritin >100 μg/L with transferrin saturation <20%) 2
- Combined iron deficiency and chronic disease (ferritin 30-100 μg/L) 2
- Thalassemia minor (low MCV with normal or low-normal RDW) 2
- Vitamin B12 or folate deficiency if macrocytosis coexists 2
- Hematology consultation for persistent unexplained anemia 1
Important Caveats
Blood transfusion is not indicated for mild anemia with slightly low MCHC; reserve transfusion for hemoglobin <7.0 g/dL in stable patients 1
Higher transfusion thresholds (8-10 g/dL) may be appropriate in patients with cardiac disease or active bleeding 1
Erythropoiesis-stimulating agents (ESAs) are not first-line treatment for low MCHC anemia 1
Technical factors can cause falsely elevated or lowered MCHC, including cold agglutinins, lipemia, and cell dehydration; repeat testing if values seem inconsistent with clinical picture 3, 4
Normal MCV, MCH, or MCHC values do not exclude iron deficiency, as these indices have only moderate diagnostic accuracy (sensitivity ~50-70%) 5