Anemia:- Part 3 – Megaloblastic Anemias, Macrocytic, Vitamin B12 and Folic Acid Deficiency, and Lab findings
June 15, 2022HematologyLab Tests
- Prepare the peripheral blood smears.
- Can take blood in the EDTA.
- Also, make a direct fresh blood smear.
- Take blood for the study of Vit. B12 and folic acid.
- A bone marrow examination may be needed.
Pathophysiology of Megaloblastic Anemias
- Megaloblastic anemia is a subgroup of macrocytic anemia characterized by defective nuclear maturation. There is defective deoxyribonucleic acid (DNA) synthesis.
- Vitamin B12 and folic acid are needed to synthesize thymidine triphosphate and convert Homocysteine to Methionine.
- There are megaloblasts, large and abnormal RBC precursors in the bone marrow, and macrocytes in the peripheral blood smear.
- White blood cells show giant metamyelocytes in the bone marrow are a characteristic feature.
- Megakaryocytes are also abnormal.
Classification of megaloblastic anemia:
- Megaloblastic anemia may be of three types:
- Anemia is caused by folate deficiency.
- Anemia is caused by Vit.B12 deficiency.
- Anemia where there is no response to either of the treatment. This third group does not respond to vitamin B12 or folic acid therapy.
Vitamin B12 deficiency causes and mechanism:
- Vitamin B12 sources are meat, eggs, and dairy products.
- Gastric parietal cells secrete the Intrinsic factor, which binds to B12 and allows its absorption in the ileum.
The deficiency of vitamin B12 causes are:
- Decreased intake in the diet.
- Poor diet.
- For vegetarians.
- Malabsorption due to any cause, e.g., gastrectomy (partial or complete), antibodies to intrinsic factor, sprue, celiac disease, malignancies (lymphomas), and parasitic infestation.
- Intestinal causes:
- Jejunal diverticulosis.
- Blind loop stricture.
- Ileal resection.
- Fish tapeworms.
- Increased demand of the body:
- During pregnancy.
- Malignant tumors.
- Enzyme deficiency.
The deficiency of Folate is seen in:
- Decreased intake.
- Poor diet.
- Inadequate use of vegetables.
- In alcoholism.
- Malabsorption like:
- Tropical sprue.
- Celiac disease.
- Gluten-induced enteropathy.
- Partial gastrectomy (some cases).
- Extensive jejunal resection.
- Pathological causes like:
- Hemolytic anemia.
- Malignant diseases like:
- Increased demand of the body:
- Malignant tumors.
- Oral contraceptives.
- Inflammatory diseases of GIT like:
- Crohn’s disease.
- Rheumatoid arthritis.
- Exfoliative dermatitis.
- Drugs like:
- Folic acid antagonists like triamterene and trimethoprim.
- If there is an enzyme deficiency.
Clinical presentation of megaloblastic anemia:
- The onset is insidious, and gradually signs and symptoms of anemia appear.
- The patient may have mild jaundice due to an excessive breakdown of RBCs.
- There is glossitis, which is the beefy-red sore tongue.
- There is angular stomatitis.
- The patient may have weight loss due to malabsorption.
- There is purpura due to thrombocytopenia.
- There is pigmentation; the cause is unknown and may be the presenting feature.
- In the case of Vitamin B12 or Folate, deficiency leads to:
- Megaloblastic anemia.
- Neuropathy is only due to a deficiency of Vitamin B12.
- Melanin skin pigmentation.
- There is a decreased osteoblastic activity.
- There may be a neural tube defect in the fetus.
Laboratory findings of megaloblastic anemia are:
- MCV is increased to 110 to 115 fl, where the normal value is 77 to 93 fl.
- MCV > 99 fL, Increased MCV (>95 ) may reach 100 to 140 µm2.
- MCH is slightly increased where the normal value is 27 to 32 pg.
- MCHC is within normal limits where the normal value is 20 to 25 g/dl.
- Low hemoglobin. Hemoglobin is typically low (may reach 2 g/dL).
- The peripheral blood smear shows macrocytosis and many hypersegmentation of neutrophils.
- Occasionally may see leucopenia and thrombocytopenia.
- Reticulocytes are not in comparison to the degree of anemia.
Peripheral blood picture in megaloblastic anemia:
- Hb is reduced to 9 to 10 G /dl.
- The total RBC count is reduced.
- WBCs are normal or decreased. There is around 5% Poly with more than 5 lobes, and normally these have 3 to 4 lobes.
- DLC shows marked neutropenia and relative lymphocytosis. There are macrocytes (macroovalocytes) or hypersegmented neutrophils; these are characteristics of megaloblastic anemia.
- Peripheral blood smears show anisocytosis poikilocytosis with Macrocytes with MCV = 100 to 140 µm2.
- Myelocytes may be seen.
- RBCs show Macrocytosis, anisocytosis, poikilocytosis, polychromasia, punctate basophilia, and occasionally nucleated RBCs.
- Platelets show thrombocytopenia and the presence of giant platelets.
- Reticulocytes are normal or decreased.
- The reticulocyte index is used to evaluate effective RBC production.
- Normally increased after blood loss or hemolysis.
- Decreased in:
- Nutritional deficiency.
- Marrow aplasia or replacement.
- Exposure to toxic agents.
- Biochemical findings are:
- High serum iron.
- Indirect bilirubin is high.
- Serum LDH is raised.
- When there is a high gastrin level indicates pernicious anemia.
- Vitamin B12 level is low in B12 deficiency in serum and RBCs.
- The folic acid level is low in folic acid deficiency in serum and RBCs.
- Antibodies to gastric cells and intrinsic factors are seen in pernicious anemia.
- An abnormal Schilling test is seen in pernicious anemia.
Bone marrow in megaloblastic anemia:
- It usually is not needed to make the diagnosis of vitamin B12 deficiency.
- It is hyperplastic with megaloblastic erythropoiesis.
- Megaloblasts and normoblasts are seen.
- Megaloblastic changes with the degree of severity of the anemia.
- Leucopoiesis is abnormal. Macropolycytes are seen. There are hypersegmented nuclei.
- The myeloid and erythroid ratio is reduced.
- Megakaryocytes are usually normal or slightly increased.
- Hemosiderin storage is normal.
- Vitamin B12 serum level is reduced where the normal values are 160 to 925 ng/dl.
- Vitamin B12 level in the RBCs is also decreased where the normal value is 72 to 512 ng/dl.
- Serum Folate level is also decreased in the folic acid deficiency, where the normal value is 10 to 15 µg /L.
- RBC folate is also reduced and may be very low. The normal value is 300 to 350 µg /L.
- Iron in plasma is raised or normal.
- Serum bilirubin is moderately raised and is predominantly unconjugated bilirubin.
- Serum LDH is also raised due to ineffective erythropoiesis. In severe cases, there is a markedly increased level.
Diagnostic tests for megaloblastic anemia are:
- The diagnostic test is an assay of Vit B12, which is <90 pg/mL.
- The associated normal level of Folate indicates a B12 deficiency.
- The diagnostic test for Folate is the estimation of the folate level.
- If Folate is <3 ng/mL with a normal B12 level suggests Folate deficiency.
- Serum homocysteine level increases with B12 or Folate deficiency.
- Antibodies against intrinsic factors strongly suggest B12 deficiency (pernicious anemia).
- Urine methylmalonic acid levels are increased in B12 deficiency.
- Schilling test is also diagnostic.
Megaloblastic anemia features and differential diagnosis:
|Clinical characteristics||Serum vitamin B12 deficiency||Serum folate deficiency||RBC folate level|
||Rare and seen in strict vegetarians||Commonly seen in alcoholics.
|Etiology for malabsorption||
|Increased demand for the body||
|Effect of drugs||Dilantin sodium||Methotrexate|
|Inheritance||Transcobalamine II deficiency||None|
|Normal biochemical picture||200 to 900 pg/mL||5 to 16 ng/mL||>150 ng/mL|
|Vit. B12 deficiency||Low <100 pg/ml||Normal or high (>16 ng/mL)||Low <150 ng/mL|
|Folic acid deficiency||Normal 200 to 900 pg/mL||Low < 3 ng/mL||Low (better test)|
|Deficiency of both||Low||Low||Low|
Summary of the Vitamin B12 and Folates deficiency and lab findings:
|Parameters||Results (Lab findings)|
|Peripheral blood smear and complete blood count||
Clinical and laboratory findings in Vitamin B12 and Folate deficiencies:
|Lab/clinical parameters||Pernicious anemia (Vit.B12 Deficiency)||Folate deficiency|
|Serum gastrin level||Increased||Increased|
|Urine methylmalonic acid||Increased||Normal|
|Chronic atrophic gastritis||Present||Absent|
|Risk for gastric carcinoma||Present||Absent|
Thanks for your team ?
Thanks for appreciation