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Mixed-deficiency (iron + B 12 or folate) anemia usually presents with high RDW and variable MCV. Recent hemorrhages typically present with high RDW and normal MCV. A false high RDW reading can occur if EDTA anticoagulated blood is used instead of citrated blood. See Pseudothrombocytopenia. By severity, elevated RDW can be classified as follows:
Normally, MCV is expressed in femtoliters (fL, or 10 −15 L), and [RBC] in millions per microliter (10 6 / μL). The normal range for MCV is 80–100 fL. If the hematocrit is expressed as a percentage, the red blood cell concentration as millions per microliter, and the MCV in femtoliters, the formula becomes
Mean corpuscular volume (MCV) is the average volume of a red blood cell and is calculated by dividing the hematocrit (Hct) by the concentration of red blood cell count. [citation needed] = [] Normal range: 80–100 fL (femtoliter)
Anisocytosis is a medical term meaning that a patient's red blood cells are of unequal size. This is commonly found in anemia and other blood conditions. False diagnostic flagging may be triggered on a complete blood count by an elevated WBC count, agglutinated RBCs, RBC fragments, giant platelets or platelet clumps due to anisocytosis.
The normal mean corpuscular volume (abbreviated to MCV on full blood count results, and also known as mean cell volume) is approximately 80–100 fL. When the MCV is <80 fL, the red cells are described as microcytic and when >100 fL, macrocytic (the latter occurs in macrocytic anemia). The MCV is the average red blood cell size.
The Mentzer index, described in 1973 by William C. Mentzer, [1] is the MCV divided by the RBC count. It is said to be helpful in differentiating iron deficiency anemia from beta thalassemia trait. [2] [3] The index is calculated from the results of a complete blood count.
A diagnosis of PA first requires demonstration of megaloblastic anemia by conducting a full blood count and blood smear, which evaluates the mean corpuscular volume (MCV), as well the mean corpuscular hemoglobin concentration (MCHC). [50] PA is identified with a high MCV (macrocytic anemia) and a normal MCHC (normochromic anemia). [54]
A low RDW has no clinical significance, but an elevated RDW represents increased variation in red blood cell size, a condition known as anisocytosis. [118] Anisocytosis is common in nutritional anemias such as iron deficiency anemia and anemia due to vitamin B12 or folate deficiency, while people with thalassemia may have a normal RDW. [118]