Investigating vitamin B12 deficiency

### What you need to know A 44 year old woman attends her general practitioner with a two year history of lethargy, which has resulted in her being unable to continue her job as a primary school teacher. She had a history of anaemia a few years ago and was not taking any regular medication, except for the combined contraceptive pill. Her mother has hypothyroidism for which she takes levothyroxine; there is no other family history of note. Physical examination was unremarkable. Recent blood tests showed haemoglobin 110 g/L (reference range 115-160) and mean corpuscular volume 102 fL (range 80-100). To further investigate the cause of her macrocytic anaemia, blood tests for vitamin B12 and folate were requested, which showed vitamin B12 138 pmol/L (reference range 148-600 (to convert from pmol/L to ng/L, multiply by 1.355)) and folate 40.5 nmol/L (4.5-45 (to convert to μg/L, divide by 2.27)). The prevalence of vitamin B12 (B12) deficiency is approximately 6-12% in adults under 60 years old and around 17% in all adults with macrocytic anaemia.123 However, elderly people, pregnant women, and vegans are more susceptible to B12 deficiency, so have a higher index of suspicion in these populations in the presence of suggestive symptoms and signs (box 1). Some …