B₁₂ DEFICIENCY

• Vitamin deficiency usually develops slowly over several months to years
• Vitamin deficiency signs and symptoms may be subtle at first
• increase as the deficiency worsens

Symptoms

Neurological

• Numbness or paraesthesia
• Muscle weakness
• Unsteady movements

Megaloblastic anaemia

• Breathlessness
• Fatigue
• Dizziness

Non-specific

• Memory loss
• Personality changes
• Mental confusion or forgetfulness
• Irregular heartbeats

Signs

• Pale or yellowish skin
• Glossitis
• Peripheral neuropathy
• especially proprioception
• Sub-acute combined degeneration of the cord
• which may occur in the absence of anaemia

Assessment

• Diet
• Features of malabsorption
• Personal/FH of autoimmune conditions
• GI surgery
• Medication use
• e.g. proton pump inhibitors, metformin, OCP
• Pregnancy and OCP
• oestrogen reduces serum B₁₂ (but not functional B₁₂)
• by 25% on oral contraceptive pill
• by <30% by third trimester of pregnancy
• level >150 pg/mL may therefore be normal

Investigations

• FBC
• Folate
• Serum cobalamin (B₁₂)
• Anti-intrinsic factor Ab (anti-IF Ab)
• if suspect PA, test for anti-IFAB regardless of cobalamin levels

Symptoms/signs of B₁₂ deficiency present

Management of low serum cobalamin (B₁₂) levels where symptoms/signs of B12 deficiency present

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B₁₂  low but symptoms/signs absent

• B₁₂ ≤ 200 pg/mL
• Non-specific symptoms

Management of low serum cobalamin (B₁₂) levels in the absence of objective clinical parameters

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Pernicious anaemia

• Prescribe vitamin B₁₂ as hydroxocobalamin
• Treatment regimens are dependent on symptoms/signs. See BNF

Dietary cause

• Dietary sources of B₁₂ include eggs, milk/dairy products, salmon, fortified products e.g. cereals
• In the absence of neuropathy, consider oral cyanocobalamin 50–250 microgram daily taken between meals (although higher doses <2000 mg may be required)
• check B₁₂ levels at 1–3 months
• Duration of B₁₂ supplementation depends on the cause of the deficiency and response
• When using oral cyanocobalamin, caution regarding possible emerging pernicious anaemia

RBC transfusion in chronic anaemia 

• Consider a single unit RBC transfusion in patients with:
• moderate/severe symptoms
• haemodynamically stable
• reversible cause of anaemia
• Hb <90 g/L
• Remember each unit transfused is a treatment decision
• See Chronic Anaemia: RBC transfusion

• If patient receiving IM hydroxocobalamin, do not routinely check B₁₂ levels
• Monitor for hypokalaemia after commencing B₁₂ replacement and consider replacement
• If PA, assess reticulocyte response at 7–10 days
• suboptimal response may indicate concomitant iron deficiency

• Inform GP of:
• cause
• treatment
• monitoring required