Hematology and Oncology Book

http://www.fpnotebook.com/

Vitamin B12 DeficiencyAka: Pernicious Anemia, B12 Deficiency, Cobalamin Deficiency

Advertisement

  1. See Also
    1. Macrocytic Anemia
    2. Vitamin B12
  2. Causes: Vitamin B12 deficiency
    1. See Medications Affecting Cobalamin
    2. Pernicious Anemia
      1. Autoimmune parietal cell destruction
      2. Results in insufficient intrinsic factor production
    3. Elderly with atrophic Gastritis (10-30% over age 60)
      1. Can not absorb Vitamin B12 bound to protein
      2. However can absorb crystalline Vitamin B12 normally
    4. Malabsorption
      1. Crohn's Disease
      2. Zollinger-Ellison Syndrome (Gastrinoma)
      3. Whipple's Disease
      4. Intestinal infection (e.g. parasite or Tapeworm)
      5. Blind Loop Syndrome (Gastrectomy and ileal resection)
    5. Inadequate Vitamin B12 intake
      1. Vegan
      2. Elderly
      3. Alcoholism
  3. Symptoms
    1. Initial
      1. Generalized weakness
      2. Paresthesias
    2. Next
      1. Leg stiffness
      2. Ataxia
    3. Late
      1. Memory Impairment
      2. Personality change
      3. Depressed mood
  4. Signs
    1. Mnemonic: "The 5 P's"
      1. Pancytopenia
      2. Peripheral Neuropathy
      3. Posterior spinal column Neuropathy
        1. Dorsal Column Degeneration
        2. Decreased proprioception
        3. Decreased vibration sense
        4. Ataxia
        5. Hyporeflexia (e.g. decreased ankle jerk)
      4. Pyramidal tract signs
      5. Papillary atrophy of Tongue (Atrophic Glossitis)
    2. Other changes
      1. Dementia
      2. Major Depression
      3. Psychosis
      4. Optic Neuritis
      5. Anorexia
  5. Labs
    1. Complete Blood Count (CBC)
      1. Anemia
        1. See Hemoglobin Cutoffs for Anemia
        2. See Hematocrit Cutoffs for Anemia
      2. Megaloblastic Macrocytic Anemia
        1. Mean Corpuscular Volume >100 um^3
        2. MCV cutoff varies by age and per reference
      3. Changes in other cell lines
        1. Leukopenia
        2. Thrombocytopenia
    2. Peripheral Blood Smear
      1. Megaloblastosis: Oval Macrocytes
      2. Hypersegmented Neutrophils
      3. Giant platelets
    3. Serum Vitamin B12 <200 pg/ml (<150 pmol/L)
      1. Neurologic changes occur in normal B12 level (50%)
      2. Low serum Vitamin B12 is poorly specific for deficiency
      3. Confirm low value with additional testing
        1. Serum Homocysteine increased
        2. Serum Methylmalonic acid increased
    4. Serum RBC Folate decreased
    5. Other lab tests
      1. Schilling Test: Radiolabeled Vitamin B12 excretion
        1. Rarely performed now
      2. Antibodies to intrinsic factor
  6. Evaluation
    1. Step 1: Obtain Vitamin B12 and Folic Acid Levels
    2. Step 2: Interpret Folic Acid Level
      1. Folic Acid Normal: Go to Step 3
      2. Folic Acid deficiency
        1. Provide Folic Acid Supplementation
        2. Return to Step 1 to recheck levels
    3. Step 3: Interpret Vitamin B12 level
      1. Vitamin B12 > 400 pg/ml: Normal, no further testing
      2. Vitamin B12 100 to 400 pg/ml: Go to Step 4
      3. Vitamin B12 < 100 pg/ml: Treat Vitamin B12 Deficiency
    4. Step 4: Obtain secondary B12 Deficiency markers
      1. Lab markers (B12 dependent reaction substrates)
        1. Serum methylmalonic acid
        2. Serum Homocysteine
      2. Interpretation
        1. Either level high: Treat Vitamin B12 Deficiency
        2. Levels normal: Normal, no further testing
    5. References
      1. Oh (2003) Am Fam Physician 67(5):979
      2. Snow (1999) Arch Intern Med 159:1297
  7. Management
    1. See Vitamin B12 Supplementation
  8. References
    1. Babior in Wilson (1991) Harrisons, McGraw, p. 1523-9
    2. Brigden (1995) Postgrad Med 97(5):171
    3. Dharmarajan (2003) {a 6611} 58(3):30
    4. Oh (2003) Am Fam Physician 67(5):979

Navigation Tree