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Why can hemoglobin concentration differ from the red blood cell count?

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blood analysis The physical and chemical properties of a sample of blood are examined during blood analysis. The examination of blood is important for the accurate diagnosis of disease.

Hemoglobin concentration and red blood cell (RBC) count can differ because they measure distinct properties of the blood. While the RBC count indicates the total number of erythrocytes present, the hemoglobin concentration measures the amount of the iron-containing protein responsible for oxygen transport.1

These values may not align due to variations in the size and hemoglobin content of individual cells. For example, in hypochromic microcytic anemia—often caused by an iron deficiency—the circulating red blood cells are smaller than normal and contain less hemoglobin. Conversely, in macrocytic anemia, the cells are larger than normal.2

Clinicians use these measurements, along with the hematocrit, to calculate the mean corpuscular volume (MCV) and the mean corpuscular hemoglobin concentration (MCHC). These indexes provide a more accurate assessment of the nature of a blood disorder than either count alone, as they reveal whether the cells are appropriately sized and adequately filled with hemoglobin.2