Hematology & immune disorders
Anemia
Vitamin B12 deficiency
Author: R. Amita, M.D.
Last author update: 1 July 2016
Last staff update: 4 October 2023
Copyright: 2002-2024, PathologyOutlines.com, Inc.
PubMed Search: Vitamin B12 deficiency [title]
Table of Contents
Definition / general | Epidemiology | Pathophysiology | Etiology | Clinical features | Diagnosis | Laboratory | Case reports | Treatment | Clinical images | Microscopic (histologic) description | Microscopic (histologic) images | Peripheral smear description | Peripheral smear images | Differential diagnosis | Additional referencesCite this page: Amita R. Vitamin B12 deficiency. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/hematologyvitaminb12deficiency.html. Accessed December 2nd, 2024.
Definition / general
- Vitamin B12 deficiency, also known as hypocobalaminemia, refers to low blood levels of vitamin B12
Epidemiology
- 6% of those under age 60 and 20% over age 60
- Rates may be as high as 80% in parts of Africa and Asia
Pathophysiology
- Total amount of vitamin B12 stored in the body is between 2 - 5 mg in adults
- Of this, 50% is stored in the liver, 0.1% is lost each day as secretions into the gut
- Most of the vitamin B12 excreted into the bile is recycled via enterohepatic circulation
- Because of this mechanism, the liver can store three to five years’ worth of vitamin B12 under normal conditions and functioning
- Deficiency of Vitamin B12 affects the metabolic pathway in 2 critical points:
- Homocysteine to methionine, catalyzed by methionine synthase needs cyanocobalamin as a cofactor; resulting hyperhomocysteinemia may lead to a prothrombotic state
- The end product methionine aids in purine and thymidine synthesis, myelin production, protein / neurotransmitters / fatty acid / phospholipid production and DNA methylation, which becomes deficient in these individuals
- Methylmalonyl-CoA to succinyl-CoA also requires Vitamin B12 as a cofactor
- Homocysteine to methionine, catalyzed by methionine synthase needs cyanocobalamin as a cofactor; resulting hyperhomocysteinemia may lead to a prothrombotic state
Etiology
- Poor absorption from the stomach or intestines
- Pernicious anemia
- Surgical removal of the stomach
- Chronic inflammation of the pancreas
- Intestinal parasites, certain medications
- Some genetic disorders
- Decreased intake
- Vegan diet
- Malnutrition
- Increased requirements
- HIV / AIDS
- Rapid red blood cell breakdown
Clinical features
- Extreme tiredness
- Lack of energy
- Pins and needles (paraesthesia)
- Sore and red tongue
- Mouth ulcers
- Muscle weakness
- Disturbed vision
- Psychological problems, which may include depression and confusion
- Problems with memory, understanding and judgement
- Rarely hyperpigmentation (Indian J Endocrinol Metab 2013;17:S254)
Diagnosis
- Vitamin B12 levels in blood below 120 – 180 picomol/L in adults
- Elevated methylmalonic acid levels (values > 0.4 micromol/L)
- Hyperhomocysteinuria is a non-specific marker of deficiency
Laboratory
- Hyperhomocysteinuria is a non-specific marker of deficiency
- Methylmalonic acid is a more specific test of B12 deficiency
Case reports
- 14 year old girl with neuropathy and ileal tuberculosis (J Med Case Rep 2008;2:90)
- 64 year old woman with confusion (Encephale 2003;29:560)
- 66 year old woman with major depressive disorder (Prim Care Companion J Clin Psychiatry 2009;11:269)
Treatment
- Oral or parenteral supplements (J Hum Nutr Food Sci 2013;1: 1008)
- When large doses (1 - 2 mg) are given by mouth, its absorption does not rely on the presence of intrinsic factor or an intact ileum - the free crystalline B12 is absorbed along the entire intestine by passive diffusion
Clinical images
Images hosted on other servers:
Hyperpigmentation before treatment
Microscopic (histologic) description
- Individuals with autoimmune gastritis may develop pernicious anemia because of extensive loss of parietal cell mass and anti-intrinsic factor antibodies
- Autoimmune gastritis is usually restricted to the gastric corpus and fundus; lymphocytes infiltrate the gastric mucosa, destroy epithelial cells and cause gastric atrophy
Microscopic (histologic) images
Images hosted on other servers:
Atrophic gastritis with intestinal metaplasia
Peripheral smear description
- Decreased red blood cell (RBC) count and hemoglobin levels
- Increased mean corpuscular volume (MCV > 100 fL) and mean corpuscular hemoglobin (MCH)
- Reticulocyte count is decreased due to destruction of fragile and abnormal megaloblastic erythroid precursor
- Platelet count may be reduced
- Neutrophil granulocytes may have hypersegmented nuclei
- Anisocytosis (increased variation in RBC size) and poikilocytosis (abnormally shaped RBCs)
- Macrocytes (larger than normal RBCs) are present
- Ovalocytes (oval-shaped RBCs) are present
- Howell-Jolly bodies (chromosomal remnant) also present
Peripheral smear images
Images hosted on other servers:
Hypersegmented neutrophil
Macrocytes, macro-ovalocytes,
nucleated RBCs and hypersegmented neutrophils
Differential diagnosis
Additional references
