Here’s how readers responded to a You Make the Call question about 42-year-old female patient who has had very low B12 levels for at least a decade.
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Measure holotranscobalamin levels.
A. Saifudeen, MBBS, MD, FRCP
Thank you for posting this difficult clinical scenario of a patient with Crohn disease and low B12 levels. Given her normal methylmalonic acid levels and no manifestation of B12 I feel somewhat reassured. Have you tried sublingual B12 or B12 patches?
Satvir Singh, MD
Back to basics: Treat the patient, not the tests.
Catherine Cole, MBBS, FRACP, FRCPA
Have you done the old time-honored Schilling test? If that is normal, I would not do any B12 quantitation, as long as she is asymptomatic.
Susumu Inoue, MD
Have you tried sublingual B12 supplements?
Daniel O. Cuscela, DO
West Palm Beach, FL
This patient obviously has low/very-low vitamin B12 levels for many years without any symptoms suggesting a vitamin B12 deficiency (neither any hematologic nor neurologic symptomatology). This is compatible with haptocorrin deficiency. Haptocorrin (previously denoted transcobalamin I and III) carry about 70 to 90 percent of the total vitamin B12 in serum, however this part of vitamin B12 is not available for most cells, such as erythroid precursors. Only vitamin B12 bound to transcobalamin (previously denoted transcobalamin II) is available for most cells, such as hematopoietic precursors. This transcobalamin-bound vitamin B12 is therefore considered to be the “active vitamin B12 ” and constitutes only 10 to 30 percent of the total measured vitamin B12.
This patient, therefore, probably has normal active vitamin B12 ; this could be confirmed by measuring specifically holotranscobalamin. The low vitamin B12 level is likely caused by low holohaptocorrin (i.e., the vitamin B12 bound to haptocorrin).
No treatment will be needed in this woman.
Bernhard Lämmle, MD