Quantification of one or more of total vitamin B12, holotranscobalamin, methylmalonic acid or homocysteine for a patient: a) who: (i) is still experiencing symptoms of vitamin B12 deficiency 3 to 6 months after a service described in item 66838 or 66839 was rendered for the patient; or(ii) obtained inconclusive results from a service described in item 66839; or b) to whom one or more of the following applies: (i) the patient has a diet low in vitamin B12;(ii) the patient has a family history of vitamin B12 deficiency or an autoimmune condition;(iii) the patient has previously had abdominal or pelvic radiotherapy;(iv) the patient has previously had surgery involving the gastrointestinal tract;(v) the patient uses, or has a recent history of using, recreational nitrous oxide;(vi) the patient requires monitoring of vitamin B12 treatment;(vii) the patient uses vitamin B12-antagonistic medicines;(viii) the patient has one or more clinical conditions with a recognised risk of vitamin B12 deficiency