What do the mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and platelet count represent in a laboratory finding?

Red Blood Cell Indices and Platelet Count: Clinical Interpretation

These laboratory parameters are fundamental measurements that characterize red blood cell size, hemoglobin content, and platelet numbers—essential for diagnosing and classifying anemias and other hematologic conditions.

Mean Corpuscular Volume (MCV)

MCV measures the average volume of individual red blood cells, reported in femtoliters (fL). 1, 2, 3

• Normal range: 80-100 fL in adults
• Measured directly by automated counters or calculated as the ratio of hematocrit to red blood cell count 1
• MCV is highest at birth, decreases during the first 6 months of life, then gradually increases during childhood to adult levels 1

Clinical Significance:

• Microcytic (MCV < 80 fL): Indicates small red blood cells

  • Most commonly caused by iron deficiency anemia 2, 3
  • Other causes: thalassemia, anemia of chronic disease, sideroblastic anemia 2
  • If lead poisoning, infection-related anemia, chronic inflammatory disease, and thalassemia minor can be excluded, a low MCV serves as a specific index for iron-deficiency anemia 1

• Normocytic (80-100 fL): Normal-sized red blood cells

  • May indicate hemorrhage, hemolysis, bone marrow failure, anemia of chronic inflammation, or renal insufficiency 2
  • In anemia of chronic disease, MCV may be normal or low 3

• Macrocytic (MCV > 100 fL): Indicates large red blood cells

  • Most commonly indicates vitamin B12 or folate deficiency 2, 3
  • Also seen with thiopurine medications (azathioprine, 6-mercaptopurine), alcohol abuse, hypothyroidism, myelodysplastic syndrome 3

Mean Corpuscular Hemoglobin (MCH)

MCH measures the average amount of hemoglobin per red blood cell, reported in picograms (pg). 3

• Reflects the hemoglobin content of individual red blood cells
• Decreases in iron deficiency anemia (microcytic, hypochromic cells) 4
• Useful alongside MCV for anemia classification 3
• Iron deficiency is indicated by MCV < 80 fL and MCH < 27 g/dL 4

Clinical Context:

• MCH values may be artificially elevated when red blood cells are coated with antibodies (positive Coombs test) or after certain medications like azathioprine 5
• Recent evidence shows MCH exhibits an inverse association with cancer risk, particularly for lymphoma, leukemia, breast cancer, and kidney cancer 6

Mean Corpuscular Hemoglobin Concentration (MCHC)

MCHC measures the average concentration of hemoglobin within red blood cells, reported in g/dL. 2, 7

• Calculated as: hemoglobin concentration divided by hematocrit
• Normal range: 27-35 g/dL 7
• Iron deficiency is indicated by MCHC < 27 g/dL 4

Critical Pitfall:

MCHC values above 36 g/dL indicate a technical problem with the sample 5, 8:

• Cold agglutinins (most common cause)
• Paraproteins
• High bilirubin levels
• Elevated leukocyte counts
• Lipemic samples 8

When MCHC is abnormally elevated, reheat the sample at 37°C for 1 hour and reanalyze. If values normalize, cold agglutinins are present; if unchanged, investigate other interfering factors 5, 8.

Red Cell Distribution Width (RDW)

RDW quantifies the variation in red blood cell size, expressed as a percentage. 1, 3

• Calculated as: (standard deviation of red blood cell volume / MCV) × 100
• Elevated RDW (> 14.0%) indicates increased variation in cell size 1

Diagnostic Algorithm:

• Low MCV + RDW > 14.0% = Iron deficiency anemia 1
• Low MCV + RDW ≤ 14.0% = Thalassemia minor 1
• High RDW is an indicator of iron deficiency, particularly useful when microcytosis and macrocytosis coexist and neutralize each other, resulting in falsely normal MCV 3

Platelet Count

Platelet count measures the number of platelets per volume of blood, reported as × 10⁹/L.

• Normal range: Varies by laboratory, typically 150-400 × 10⁹/L
• Critical for assessing bleeding and clotting risk
• Platelet count is higher in females than males 9

Technical Consideration:

In microcytic anemia (MCV < 80 fL), impedance-based platelet counts may be falsely elevated due to small red blood cells being counted as platelets 10. When MCV < 72.9 fL, use optical platelet counting methods for accurate results 10.

Integrated Diagnostic Approach

The minimum workup for anemia should include: 3

• Complete blood count with MCV, MCH, MCHC
• Reticulocyte count
• Red cell distribution width (RDW)
• Serum ferritin
• Transferrin saturation
• C-reactive protein (CRP)

For iron deficiency diagnosis: 4, 11, 3

• Without inflammation: Ferritin < 30 μg/L indicates iron deficiency
• With inflammation present: Ferritin up to 100 μg/L may still indicate iron deficiency
• Transferrin saturation < 20% with ferritin 30-100 μg/L suggests combined iron deficiency and anemia of chronic disease 11