A number of red blood cell tests are performed together in a complete blood count (CBC). These tests (called red cell indices) are assessed together to point to specific causes of red blood cell dysfunction. These tests include:
Red blood count: The count of all red blood cells in a volume of blood
- Adult women: 3.9-5.0 million cells/µL
- Adult men: 4.3-5.7 million cells/µL
- Please refer to previous posts for detailed discussion of causes of low and high RBC.
Hemoglobin (Hb): The amount of hemoglobin in a volume of blood
- Adult women: 12.0-15.5 grams/dL
- Adult men: 12.5-17.5 grams/dL
- Hemoglobin constitutes about 95% of the mass of a red blood cell.
- Hemoglobin binds oxygen so that red cells can carry them through the blood into the tissues.
- Common causes of low hemoglobin include vitamin or mineral deficiency, chronic inflammation, autoimmune disease, hemoglobinopathies, thalassemia, GI bleeding, surgery and blood loss.
- Common causes of high hemoglobin include lung disease, neoplastic conditions including cancers, and dehydration.
- If red blood cell count and hematocrit are low, usually hemoglobin is low, too. If red blood cell count and hematocrit are high, usually hemoglobin is high, too.
- Even if red blood cell count is normal, low hemoglobin will cause symptomatic anemia.
- Anemia is a decreased ability to carry oxygen from lungs to tissues.
Hematocrit (HCT): The portion of a volume of blood that is red blood cells
- Adult women: 34.0-44.5%
- Adult men: 38.8-50.0%
- Equal to (red blood cell count)/(volume of blood measured)
- Used to assess severity of blood loss.
- Common causes of low hemoglobin include vitamin or mineral deficiency, chronic inflammation, autoimmune disease, hemoglobinopathies, thalassemia, GI bleeding, surgery and blood loss.
- Common causes of high hemoglobin include lung disease, neoplastic conditions including cancers, and dehydration.
- If red blood cell count and hemoglobin are low, usually hematocrit is low, too. If red blood cell count and hemoglobin are high, usually hematocrit is high, too.
Definitions:
- Microcytic anemia: low MCV
- Normocytic anemia: normal MCV
- Macrocytic anemia: high MCV
- Hypochromic anemia: low MCH
- Normochromic anemia: normal MCH
- Hyperchromic anemia: high MCH
Mean corpuscular volume (MCV): Identifies if red cells are the right size
- 80-96 fL/cell
- Equal to (hematocrit)/(red blood cell count)
- The size of red cells tells you what causes anemia.
- Low MCV with low red cell count and low hemoglobin indicates microcytic anemia.
- Common causes of microcytic anemia (low MCV) include iron deficiency, blood loss, anemia of chronic inflammation, sideroblastic anemia, thalassemia, pyridoxine deficiency and lead poisoning.
- High MCV with low red cell count and low hemoglobin indicates macrocytic anemia.
- Common causes of macrocytic anemia (high MCV) include megaloblastic anemia, alcoholism, COPD, hypothyroidism, MDS, liver disease and deficiency of vitamin B12 and/or folate.
Mean corpuscular hemoglobin (MCH): The average hemoglobin in a red blood cell in a volume of blood
- 5-33.2 pg/cell
- Equal to (hemoglobin)/(red blood cell count)
- MCH usually mirrors MCV. If MCV is low, MCH is usually low. If MCV is high, MCH is usually high.
- Common causes of low MCH include iron deficiency, blood loss, anemia of chronic inflammation, sideroblastic anemia, thalassemia, pyridoxine deficiency and lead poisoning.
- Common causes of high MCH include megaloblastic anemia, alcoholism, COPD, hypothyroidism, MDS, liver disease and deficiency of vitamin B12 and/or folate.
Mean corpuscular hemoglobin concentration (MCHC): Determines size of red cells
- 4-35.5 g/dL
- Equal to (hemoglobin)/(hematocrit)
- Low MCHC is associated with hypochromic (“too little color”) anemia. Cells with less hemoglobin have less intense red color. Patients with hypochromic anemia often have a green tinge to their skin.
- MCHC is usually low in microcytic anemia.
- MCHC is sometimes normal in some macrocytic anemias. This is called normochromic anemia (“normal color”).
- Common causes of low MCHC include thalassemia, vitamin B6 deficiency, lead poisoning, Faber’s syndrome, GI bleeding and iron deficiency.
- Common causes of normal MCHC in the presence of anemia (normocytic anemia) include anemia of chronic inflammation, aplastic anemia, blood loss, hemolysis, and deficiency of vitamins B2 or B6.
- High MCHC is associated with hyperchromic (“too much color”) anemia.
- Common causes of high MCHC include sickle cell disease, hereditary spherocytosis, autoimmune hemolytic anemia and hemoglobin C disease.
Red blood cell distribution width (RDW): The amount of variation in the size of red cells
- 5-14.5%
- RDW is normal or high. A “low” RDW should be read as normal.
- RDW helps to identify the cause of anemia.
- A high RDW indicates that there are large amounts of both new and mature red cells.
- Variation in size of red cells is called anisocytosis.
- Common causes of high RDW include
Reticulocyte count: The amount of new red cells in a volume of blood
- 5-1.5%
- Elevated reticulocyte count is called reticulocytosis.
- Common causes of reticulocytosis include hemolytic anemia, pernicious anemia, deficiency of iron, vitamin B12 or folate, anemia of chronic inflammation, cancers affecting bone marrow and chemotherapy.
In conditions with low RBC, low hemoglobin and/or low hematocrit:
- Low MCV with high RDW: Iron deficiency anemia
- High MCV with high RDW: Vitamin B12 and/or folate deficiency
- Variable MCV (low, high or normal) with high RDW: Mixed deficiency (iron and B12 or folate)
- Normal MCV with high RDW: Large blood loss (hemorrhage)
- Normal MCV with normal MCH: chronic illness, aplastic anemia, prosthetic heart valves, sepsis or kidney failure
- Low MCV with low MCH: iron deficiency, thalassemia, lead poisoning, long term inflammation
- High MCV with normal or high MCH: deficiency of B12 or folate