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Red Blood Cell (RBC) Indices
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Red Blood Cell (RBC) Indices

RBC indices provide detailed information about the size, shape, and hemoglobin content of your red blood cells to help diagnose different types of anemia.

Overview

Red blood cell (RBC) indices are measurements that describe the physical characteristics of your red blood cells (erythrocytes). These indices are typically part of a complete blood count (CBC) and are used to identify the specific type of anemia you may have.

The Four RBC Indices

  • Mean corpuscular volume (MCV): Measures the average size of your red blood cells.
  • Mean corpuscular hemoglobin (MCH): Measures the average amount of hemoglobin in a single red blood cell.
  • Mean corpuscular hemoglobin concentration (MCHC): Measures the concentration of hemoglobin within your red blood cells.
  • Red cell distribution width (RDW): Measures the variation in the size and volume of your red blood cells.

Why do I need this test?

You may receive this test during a routine checkup or if you show symptoms of anemia, such as fatigue, weakness, dizziness, shortness of breath, pale skin, or cold hands and feet.

What do the results mean?

Abnormal results help your provider narrow down the cause of anemia:

MCV (Size)

  • Smaller than normal: May indicate iron deficiency anemia or thalassemia.
  • Larger than normal: May indicate vitamin B deficiency or liver disease.

MCH (Hemoglobin Amount)

  • Lower than normal: Often linked to iron deficiency anemia.
  • Higher than normal: Often linked to vitamin B deficiency.

MCHC (Hemoglobin Concentration)

  • Lower than normal: May indicate iron deficiency anemia or thalassemia.
  • Higher than normal: May indicate hemolytic anemia or hereditary spherocytosis.

RDW (Size Variation)

Normal results indicate that your red blood cells are uniform in size. Abnormal results indicate a variation in size, which is used in conjunction with other indices to confirm a diagnosis.

Because no single index is sufficient for a diagnosis, your provider will interpret these results alongside your symptoms, medical history, and other blood tests.

Frequently Asked Questions

high RDW indicates variability in red blood cell size. This can occur in early iron deficiency, vitamin B12 or folate deficiency, or after recent blood loss. Even if hemoglobin is within normal limits, a high RDW can signal that the bone marrow is producing cells of different sizes, prompting further evaluation of nutrient status or hidden bleeding.
If any of the indices (MCV, MCH, MCHC, RDW) are outside the reference range, a repeat CBC in 4–6 weeks is useful to assess response to treatment or to detect evolving anemia. Persistent abnormalities may warrant additional tests such as reticulocyte count, iron studies, vitamin B12/folate levels, or a bone marrow evaluation.
Low MCHC often points to iron deficiency or thalassemia. Increasing dietary iron (heme iron from red meat, iron‑fortified cereals, or plant sources with vitamin C to enhance absorption) and avoiding inhibitors such as tea or coffee during meals can raise MCHC. If iron deficiency is confirmed, oral iron supplements and monitoring of ferritin levels are recommended.
In iron deficiency anemia, the MCV is typically low (microcytic). A value below 80 fL suggests that iron stores are depleted. Your clinician may order ferritin, transferrin saturation, or a complete iron panel to confirm iron deficiency and guide iron supplementation.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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