1. Risk factors
1.1. African, Northern European decent
1.2. Family history
1.3. Removal or partial removal of stomach or small intestines
1.4. Autoimmune disorders involving endocrine glands such as type 1 DM
1.5. Intestinal disorders that affect absorption such as Chron's, celiac disease, HIV
1.6. Antibiotics/Seizure medication
1.7. Vegetarian diet
2. Diagnostic Test
2.1. complete blood count
2.1.1. Hemoglobin
2.1.2. Hematocrit
2.1.3. Red blood cell
2.1.4. Platelet
2.1.5. Mean corpuscular volume
2.1.6. Reticulocyte count
2.2. Serum folate, iron binding capacity
2.3. Vitamin B12 level
2.4. Homocysteine level
2.5. Methylmalonic acid level
2.6. Intrinsic factor and parietal cell antibodies
2.7. Bone marrow aspiration and biopsy
3. Treatment
3.1. Intramuscular/oral Vitamin B12 supplamentation
3.2. Monitoring of symptoms and biochemical markers
4. Pathophysiologic etiology
4.1. Loss of parietal cells
4.1.1. no intrinsic factor realeased
4.1.1.1. vitamin b12 unable to be absorbed by intestine
4.1.1.1.1. Accumulation of homocysteine
4.1.1.1.2. Pyrimidine bases unable to from
4.1.1.1.3. Accumulation of methylmalonic acid
4.2. Alteration in intestinal flora or parasitic infection
4.2.1. Intake of vitamin B12 by intestinal microorganism instead of intestine
4.3. Insufficient dietary intake of vitamin B12
5. Common Findings
5.1. Anemia
5.1.1. Fatigue
5.1.2. Shortness of breath
5.1.3. dizziness
5.1.4. headache
5.1.5. Chest pain
5.1.6. Palor
5.1.7. Tachycardia
5.2. Neurologic
5.2.1. Tingling/numbness
5.2.2. Weakness
5.2.3. Decreased reflexes
5.2.4. Peripheral neuropathy
5.2.5. Ataxia
5.3. Gastrointestinal
5.3.1. Nausea/Vomiting
5.3.2. Heartburn
5.3.3. Bloating, constipation, diarrhea
5.3.4. Loss of appetite, weight loss
6. Atrophic gastritis
6.1. Helicobacter pylori infection
6.1.1. Inflammation of gastric mucosa
6.1.1.1. Loss of parietal cells
6.1.2. Immune response
6.2. Autoimmune
6.2.1. Loss of T cell function
6.2.1.1. autoantibodies destroy parietal cells and intrinsic factor