Source: Cook K, Ineck BA,
Lyond WL. Anemias. In: DiPiro, JT, Talbert RL, Yee GC, Matzke GR,
Wells BG, Posey LM. Pharmacotherapy: A Pathophysiologic Approach.
8th ed. http://www.accesspharmacy.com/content.aspx?aid=7999561.
Accessed June 12, 2012.
- Decreased oxygen-carrying capacity of blood characterized
by a decrease in hemoglobin (Hb) or red blood cells (RBCs)
- World Health Organization (WHO definition)
Hb <13 g/dL (<130 g/L; <8.07 mmol/L)
- Women: Hb <12 g/dL (<120 g/L; <7.45
- Major causes of vitamin B12 deficiency
- Inadequate dietary intake
- Decreased absorption
- Pernicious anemia: Deficiency
of intrinsic factor can cause decreased absorption of vitamin B12
- Chronic gastritis due to Helicobacter
- Inadequate utilization
- Vitamin B12 functions
- With folate
in the synthesis of building blocks for DNA and RNA
- In maintaining the integrity of the neurologic system
- In fatty acid biosynthesis and energy production
- Vitamin B12 deficiency develops over several years
of deprivation because of efficient enterohepatic circulation and
- Macrocytic, megaloblastic anemia
- Increasing age
- Use of gastric acid–suppressing agents
- Neurologic findings often precede hematologic findings
and may occur in the absence of anemia.
- Neurologic findings
- Numbness and paraesthesias
- Peripheral neuropathy
- Diminished vibratory sense
- Decreased proprioception
- Vision changes if optic nerve is involved
- Psychiatric findings
- Personality changes
- Memory impairment
- In children: prolonged deficiency can lead to poor brain development
- Mild icterus
Means of Confirmation
- Reticulocyte count
- Vitamin B12 serum levels
pg/mL (<111 pmol/L), together with appropriate
peripheral smear and clinical symptoms, is diagnostic of vitamin
- Serum homocysteine
- Serum methylmalonic acid (MMA)
>1000 nmol/L can confirm diagnosis.
- Shilling test to help identify intrinsic factor deficiency
- Bone marrow aspirate
- Folic acid deficiency (another cause of megaloblastic
- Myelodysplastic syndrome (another cause of macrocytic anemia)
- Other causes of neurologic symptoms
- Reversal of hematologic manifestations
- Replacement of body stores
- Prevention or resolution of neurologic manifestations
- Early treatment is critical. Neurologic damage may be
irreversible if vitamin B12 deficiency not detected and
corrected within months.
- Counsel patients on types of food high in vitamin B12.
- Oral vitamin B12 supplementation appears to be
as effective as parenteral, even in patients with pernicious anemia, because
alternate vitamin B12 absorption pathway is independent
of intrinsic factor.
- Initiate oral cobalamin 1–2
mg daily for 1–2 weeks, followed by 1 mg daily.
- Parenteral vitamin B12 may also be used. Recommended
- Cyanocobalamin 1000 mcg IM daily for 1
week, then weekly for 1 month, and then monthly.
- Cyanocobalamin 100 mcg IM daily ...