In several articles on this website, we have explained when and how to order and interpret laboratory tests related to vitamin B12 deficiency. For links to those articles, please see the Related Pages section below.
For one of my outpatients, to whom I prescribed metformin for antipsychotic-induced weight gain, I ordered a serum vitamin B12 level. In another article on this website, we noted that this should be done once a year in all patients on metformin.
I put in all the psychiatric and non-psychiatric diagnosis codes that I thought applied to this patient, including the following non-psychiatric codes:
E66.9 Obesity, unspecified
R73.03 Prediabetes
E78.1 Pure hypertriglyceridemia
G47.33 Obstructive sleep apnea
Sometime later, I got a notice from Labcorp, a major laboratory chain in the United States, requesting additional diagnosis codes because the patient’s insurance company had denied payment for vitamin B12 testing. Below is a screenshot from the denial letter:
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