Megaloblastic Anemia and Other Causes of Macrocytosis

Abstract

The term macrocytosis refers to a blood condition in which red blood cells (RBC) are larger than normal. Macrocytosis is reported in terms of mean corpuscular volume (MCV). Normal MCV values range from 80 to 100 femtoliters (fl) and vary by age and reference laboratory. 1 MCV is calculated according to the following formula:Macrocytosis can be identified by reviewing peripheral blood smears and/or by automated RBC indices. The peripheral blood smear is more sensitive than RBC indices for identifying early macrocytic changes because the MCV represents the mean of the distribution curve and is insensitive to the presence of small numbers of macrocytes. 2 However, compared to the peripheral blood smear, MCV may underestimate macrocytosis in over 30% of cases. 3 Although determination of the MCV by automated blood cell counter is rarely inaccurate, hyperglycemia, marked leukocytosis and cold agglutinins may result in false elevations of the MCV. [4][5][6] Moreover, partial occlusion of the instrument aperture and/or leaving the blood sample at room temperature for several hours may also result in false elevations of the MCV value. Clinical SignificanceMacrocytosis is a relatively common finding in the era of automated blood cell counters, with prevalence estimates ranging from 1.7% to 3.6%. 3,7,8 Its significance tends to be underestimated by physicians, since about 60% of patients present without associated anemia, 8 unless there are other accompanying abnormalities noted.No complications arise from macrocytosis itself as an isolated finding. However, its identification can provide important information regarding the presence of an underlying disease state. Thus, in the appropriate clinical setting, MCV values above the upper limit of normal or those that differ significantly from the patient's baseline values may require further clinical and laboratory assessment to determine the underlying cause of the macrocytosis. 9

Megaloblastic anemia in a teenage patient

“…This in turn will go a long way in preventing the unnecessary and excessive use of antibiotics. 10 r e f e r e n c e s…”

“…10 Vegetarian diets are subclassified into lactovegetarian, (diet includes only dairy products), ovovegetarian (diet includes only eggs) and lactoovovegetarian (diet includes both dairy products as well as eggs). Vegan diets are those which exclude all animal products.…”

“…However, megaloblastic anemia, solely as the cause of pyrexia, is indeed very rare. 10 The presence of severe pallor prompted an urgent initiation of a battery of investigations to find out its exact etiology. The PBS and bone marrow findings, augmented by a low serum iron and vitamin B12 levels confirmed the diagnosis of megaloblastic anemia due to vitamin B12 deficiency.…”

105 Cases of Macrocytosis- Etiologic Profile Reflecting Lifestyle Changes

“…Severe hyperglycemia, leukocytosis, cold agglutinins and presence of a paraprotein as in multiple myeloma can lead to artifacts of electronic cell sizing. [3] [12] Moreover partial occlusion of instrument aperture, leaving the blood sample at room temperature for several hours may also result in false elevations in MCV value. [12] Cold agglutinins make RBCs clump, making them appear larger to automatic cell counters.…”

“…Homocysteine levels are elevated in both while MMA is raised only in vitamin B12 deficiency. [12] Many drugs can cause folate deficiency. Valproic acid which is an anticonvulsant, inhibits mitochondrial folate metabolism.…”