Chapter 100. Megaloblastic Anemias (Part 7)

Ineffective Hemopoiesis There is an accumulation of unconjugated bilirubin in plasma due to the death of nucleated red cells in the marrow (ineffective erythropoiesis). Other evidence for this includes raised urine urobilinogen, reduced haptoglobins and positive urine hemosiderin, and a raised serum lactate dehydrogenase. A weakly positive direct antiglobulin test due to complement can lead to a false diagnosis of autoimmune hemolytic anemia.Causes of Cobalamin DeficiencyCobalamin deficiency is usually due to malabsorption. The only other cause is inadequate dietary intake.Inadequate Dietary IntakeAdultsDietary cobalamin deficiency arises in vegans who omit meat, fish, eggs, cheese, and other animal products from their...
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Chapter 100. Megaloblastic Anemias (Part 7) Chapter 100. Megaloblastic Anemias (Part 7) Ineffective Hemopoiesis There is an accumulation of unconjugated bilirubin in plasma due to thedeath of nucleated red cells in the marrow (ineffective erythropoiesis). Otherevidence for this includes raised urine urobilinogen, reduced haptoglobins andpositive urine hemosiderin, and a raised serum lactate dehydrogenase. A weaklypositive direct antiglobulin test due to complement can lead to a false diagnosis ofautoimmune hemolytic anemia. Causes of Cobalamin Deficiency Cobalamin deficiency is usually due to malabsorption. The only other causeis inadequate dietary intake. Inadequate Dietary Intake Adults Dietary cobalamin deficiency arises in vegans who omit meat, fish, eggs,cheese, and other animal products from their diet. The largest group in the worldconsists of Hindus, and it is likely that many millions of Indians are at risk ofdeficiency of cobalamin on a nutritional basis. Subnormal serum cobalamin levelsare found in up to 50% of randomly selected, young, adult Indian vegans, but thedeficiency usually does not progress to megaloblastic anemia since the diet ofmost vegans is not totally lacking cobalamin and the enterohepatic circulation ofcobalamin is intact. Dietary cobalamin deficiency may also arise rarely innonvegetarian individuals who exist on grossly inadequate diets because ofpoverty or psychiatric disturbance. Infants Cobalamin deficiency has been described in infants born to severelycobalamin-deficient mothers. These infants develop megaloblastic anemia at about3–6 months of age, presumably because they are born with low stores ofcobalamin and because they are fed breast milk of low cobalamin content. Thebabies have also shown growth retardation, impaired psychomotor development,and other neurologic sequelae. Gastric Causes of Cobalamin Malabsorption See Tables 100-3 and 100-4. Table 100-3 Causes of Cobalamin Deficiency Sufficiently Severe toCause Megaloblastic Anemia Nutritional Vegans Malabsorption Pernicious anemia Gastric causes Congenital absence of intrinsic factor or functional abnormality Total or partial gastrectomy Intestinal Intestinal stagnant loop syndrome: jejunalcauses diverticulosis, ileocolic fistula, anatomic blind loop, intestinal stricture, etc. Ileal resection and Crohns disease Selective malabsorption with proteinuria Tropical sprue Transcobalamin II deficiency Fish tapeworm