Patent ID: 8202507

Claim:
A method of determining absorption of vitamin B12 in a subject, said method comprising: (a) orally administering B12 labeled with 14 C, 13 C, deuterium, or tritium to said subject, wherein the specific activity of the labeled B12 is at least 10 Ci/mol and the B12 mass is less than 10 μg; (b) taking a blood sample from said subject, (c) subjecting said blood sample to mass spectroscopy and measuring elevation of 14 C, 13 C, or tritium associated with the labeled B12 above background 14 C, 13 C, deuterium, or tritium concentrations, respectively and (d) comparing said concentration of labeled B12 found in the subject to the concentration of B12 in subjects with normal B12 absorption to determine the B12 absorption in the subject.