vitamin b12 injection medication or for certain illness or disease like anemia Compounded Hydroxocobalamin (Vitamin B12) Injection
Description
Normal ranges are 500-900 pg/mL

Although prion diseases primarily affect the central nervous system, causing neurodegenerative conditions, prions can also spread to other tissues, such as lymphoid organs, sometimes resulting in systemic involvement

Semin Cell Dev Biol 2011;22:61923

People who are B12 deficient either dont get enough of the nutrient in their diet, or they have a difficult time absorbing the nutrient
"How Nature builds the pigments of life" (PDF)

NHS website
