Low Vitamin B12 (deficiency)

Quick Overview

  • Normal B12: ≥180 ng/L → No further action if asymptomatic
  • Borderline B12: 145–180 ng/L → Check IFAB if high clinical suspicion
  • Low B12: <145 ng/L → Start treatment straight away, also send IFAB

If B12 is <145 ng/L and NO neurological symptoms

  • Do NOT wait for IFAB before starting treatment
  • Start IM hydroxocobalamin 1 mg three times a week for 2 weeks
  • Then:
    • If cause is dietary (e.g. vegan): use oral B12 daily (OTC 50-150 mcg)
    • If non-dietary (e.g. pernicious anaemia): continue IM every 3 months for life

If B12 is <145 ng/L and NEUROLOGICAL symptoms

  • Seek specialist advise (neuro/gastro etc.. depending on cause)
  • Start IM hydroxocobalamin 1mg every other day immediately
  • Continue until symptoms improve or stabilise
  • Then continue IM every 2-3 months for life (if advised by specialist)
  • Do not wait for blood tests before starting treatment

Neurological symptoms to watch for:

  • Pins and needles (usually in hands or feet)
  • Unsteady gait or frequent falls
  • Burning or numbness in limbs
  • Memory issues or cognitive decline
  • Visual disturbance (e.g. blurred vision)
  • Mood or psychiatric changes (e.g. depression, confusion)

If B12 is 145–180 ng/L

  • Only check IFAB if patient has symptoms or strong suspicion (e.g. vegan, atrophic gastritis)
  • If IFAB is positive → manage as pernicious anaemia
  • If IFAB negative + no symptoms → reassure and monitor or trial OTC B12

When to Refer or Seek Advice

  • No improvement in Hb after 3 months of treatment
  • Neurological symptoms are progressing
  • Unclear cause (e.g. negative IFAB, non-dietary)
  • Use local referral pathways (ERS, Consultant Connect)
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