Vitamin B12 deficiency

Vitamin B12 deficiency is a state in which the body lacks enough cobalamin for normal blood-cell production and nervous-system function. It can cause megaloblastic anemia, neurological damage, and cognitive symptoms.

Vitamin B12 metabolism: The absorption, transport, cellular uptake, and use of cobalamin in the body. Deficiency develops when any step in cobalamin handling fails.
Serum vitamin B12 test: A blood test that measures circulating vitamin B12 concentration. It is commonly used to assess suspected deficiency.
Vitamin B12: An essential water-soluble vitamin required for DNA synthesis and normal nervous-system function. Deficiency is the clinical consequence of inadequate available vitamin B12.
Folate deficiency: A lack of folate that can impair DNA synthesis and cause megaloblastic anemia. It can resemble B12 deficiency in blood tests but does not typically cause the same nerve injury.
Megaloblastic anemia: An anemia marked by abnormally large, immature red-cell precursors caused by impaired DNA synthesis. Low B12 disrupts DNA synthesis in developing blood cells.
Methylmalonic acid test: A blood or urine test that measures methylmalonic acid concentration. An elevated result can clarify borderline B12 measurements.
Vitamin B12 malabsorption: Impaired uptake of dietary or supplemental vitamin B12 from the digestive tract. Absorption failure is a major route to deficiency despite adequate intake.
Iron-deficiency anemia: An anemia caused by insufficient iron for hemoglobin production, often producing small red blood cells. Its microcytic pattern contrasts with the macrocytosis commonly associated with B12 deficiency.
Subacute combined degeneration: Progressive damage to spinal-cord pathways that can impair vibration sense, position sense, and movement. B12-related nerve injury can produce this characteristic spinal-cord syndrome.
Pernicious anemia: An autoimmune disorder in which impaired intrinsic-factor production causes vitamin B12 malabsorption. It is a frequent cause of B12 deficiency and changes long-term treatment needs.

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