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Macrocytosis is a condition where red blood cells are larger than normal. [1] These enlarged cells, also known as macrocytes, are defined by a mean corpuscular volume (MCV) that exceeds the upper reference range established by the laboratory and hematology analyzer (usually >110 fL). [2]
In pernicious anemia (macrocytic), MCV can range up to 150 femtolitres. [4] (as are an elevated GGT and an AST/ALT ratio of 2:1). Vitamin B12 and/or folic acid deficiency has also been associated with macrocytic anemia (high MCV numbers).
Folate and vitamin B 12 deficiency anemia usually presents with high RDW and high MCV. 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.
Macrocytic anemias have several causes but with the implementation of folic acid fortification in North America, folate deficiency has become a rare cause of megaloblastic macrocytic anemia in that part of the world. [1] In this region, Vitamin B 12 deficiency is a far more common cause of megaloblastic macrocytic anemia. [1]
Polycythemia is defined as serum hematocrit (Hct) or hemoglobin (HgB) exceeding normal ranges expected for age and sex, typically Hct >49% in healthy adult men and >48% in women, or HgB >16.5 g/dL in men or >16.0 g/dL in women. [8] The definition is different for neonates and varies by age in children. [9] [10]
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]
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.
Increased mean corpuscular volume (MCV, >100 fL) and mean corpuscular hemoglobin (MCH) Normal mean corpuscular hemoglobin concentration (MCHC, 32–36 g/dL) Decreased reticulocyte count due to destruction of fragile and abnormal megaloblastic erythroid precursor. The platelet count may be reduced. [8]