MCHC and Anemia Definition
MCHC (Mean Corpuscular Hemoglobin Concentration) is not used to define anemia itself, but rather to classify the type of anemia once it has been diagnosed by hemoglobin or hematocrit levels. Anemia is defined by hemoglobin concentration below age- and sex-specific thresholds, not by MCHC values 1, 2.
How Anemia is Actually Defined
Anemia diagnosis requires:
- Hemoglobin <13 g/dL for men
- Hemoglobin <12 g/dL for women 3
- For children, age-specific cutoffs apply (e.g., <11.0 g/dL for ages 6 months-5 years) 4
Hemoglobin is preferred over hematocrit because it has better reproducibility across laboratories and is not affected by storage time or patient variables like serum glucose 2.
Role of MCHC in Anemia Classification
Once anemia is confirmed by low hemoglobin, MCHC helps classify the anemia type:
Normal MCHC (Normochromic Anemia)
- Typically 32-36 g/dL
- Seen in anemia of chronic disease, chronic kidney disease 2
- Most CKD-related anemia is normochromic and normocytic 2
Low MCHC (Hypochromic Anemia)
- Indicates iron deficiency anemia when combined with low MCV 1, 4
- However, MCHC is a late marker of iron deficiency 2
- Modern automated analyzers show MCHC often remains normal even in iron deficiency except in severe cases 5
High MCHC
- Values significantly above reference range are not physiologically possible due to hemoglobin solubility limits 6
- Elevated MCHC usually indicates interference (cold agglutinins, lipemia) or hemolytic conditions requiring peripheral smear review 7, 6, 8
Practical Clinical Algorithm
Step 1: Measure hemoglobin to diagnose anemia using sex/age-specific cutoffs
Step 2: If anemia present, obtain complete blood count including:
- MCV (mean corpuscular volume) - primary classifier
- MCHC
- RDW (red cell distribution width)
- Reticulocyte count 2, 4
Step 3: Classify by MCV first:
- Microcytic (MCV <80 fL): Check iron studies, ferritin, transferrin saturation 1, 2
- Normocytic: Evaluate for chronic disease, hemolysis, bone marrow disorders 9
- Macrocytic (MCV >98 fL): Check B12, folate, thyroid function 10, 9
Step 4: Use MCHC as supporting data, not primary diagnostic criterion
Critical Pitfall
Do not rely on MCHC alone for iron deficiency diagnosis. Serum ferritin (<30 μg/L without inflammation, <100 μg/L with inflammation) and transferrin saturation are far more sensitive and specific markers 3, 4, 3. MCV is more useful than MCHC for initial anemia classification 1, 2, 4.