I recently had a routine checkup (52-y-o male) with standard blood work. I got a call from the doctor s office that everything was good on the blood work. I had requested the results be sent to me. A few days later I got them, and everything was within the normal range (magnesium was literally on the lower edge of the range), except my B12 levels, which were incredibly high. I had 1703 pg/mL, and normal was given as 243-894. I take a B12 supplement (at my doctor s suggestion a few years ago), but understand that supplements do not affect blood serum levels. I came across a Dec. 2013 study from Denmark (Arendt et al.) that showed high B12 levels associated with an increased risk of certain cancer diagnoses in subsequent years, primarily the first year after the high level was noted. Something like 6-7% of those with high levels had cancer detected in the next year. My question is, should I follow up with anything despite no apparent concern from my doctor?