Help needed - B12 Binding Capacity test result


Senior Member
Western Nebraska

Maybe you can glean some nuggets from the references given in this article by LabCorp about their UBBC test.

I had some journal references in my files that might interest you. And maybe not, because I'm doubtful any of them seem to address TCII deficiency.
Mild Transcobalamin I (Haptocorrin) Deficiency and Low Serum Cobalamin Concentrations
Conclusions: Mild TC I/HC deficiency is frequently associated with low cobalamin, is often familial, and its biochemical phenotype appears identical to the heterozygous state of severe TC I/HC deficiency. Severe TC I/HC deficiency also appears to be more common than suspected. Both diagnoses should be considered in all patients with unexplained serum low cobalamin. Genome-wide association study identifies novel loci associated with serum level of vitamin B12 in Chinese men.
Although previous genome-wide association studies (GWAS) identified several genes, including FUT2, CUBN, TCN1 and MUT, that may influence VitB12 levels in European populations, common genetic determinants of VitB12 remain largely unknown, especially in Asian populations.
Inherited cobalamin malabsorption. Mutations in three genes reveal functional and ethnic patterns
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Senior Member
From the reading I've done on it, it sounds like the UBBC represents a deficiency in carriers, which essentially means you have enough serum b12 floating around but probably not enough of it getting into the cells. The mystery is whether it's a TCI/III deficiency or a TCII which would seem more serious.

The aymptoms I've been dealing with past 4 years include nausea, bloating, extreme weight loss pretty much muscle as I was in great shape prior, brain fog, POTS, low bp, muscle aches, chills w/o fever, mild anemia, very easy brushing with prolonged heal time, feelings of muscle tightness, and a few others.

My diagnosis was Lyme disease but this makes me wonder if it is incorrect or if there is another piece to the puzzle. If the UBBC is reflecting even a mildly low TCII it would seem to point towards not enough b12 in the cells them self.

If the wheelbarrow was full to use the reference above, reflected by UBBC being low, I would expect serum b12 to be especially high, not 400 or even 500. But I might be understanding exactly how the process works incorrectly.

All I know is that the research papers on true hereditary TCII deficiency all show normal serum b12 and low UBBC as lab findings. Scientists have also started finding that true Heridatary TCII isn't the only possible issue, and that there can be 'mild' deficiency or partial, still causing issues.
Well this is a very old thread, but I want to make some important clarifications here.

Lynch's analogy of a wheelbarrow and dirt to represent the UBBC test and B12 is right. UBBC measures the available capacity of the wheelbarrow not filled by dirt.

Here is the problem: there are two main classes of binding proteins as you have noted: haptocorrin (TCI and TCIII) for the inactive form and transcobalamin (TCII) for the active form. TCII is the only protein that carries active B12, and unfortunately, only 5% to 20% of the B12 in the body is bound to TCII. 80% of the B12 in the body is bound to TCI or TCIII ("haptocorrin"). This makes it confusing when you say that studies of hereditary TCII deficiency measure normal serum B12 and low UBBC. One might expect a person with low TCII to have normal TCI and TCIII, thus normal B12 and normal UBBC. That's just simple weighting of the variables, if TCI and TCIII hold 80% of the bound B12 and are unaffected by the low TCII.

Does anyone have some PubMed studies of hereditary TCII deficiency reporting the lab findings with UBBC? I would love to read their explanation.

I find it really frustrating that B12 lab testing is incredibly primitive and does not reflect well the complexity of the biochemistry. If they developed a UBBC test, why can they not develop a test that reports the total amount of TCI, TCII, and TCIII, and then report the binding saturation for each of those proteins separately? That's the level of detail that we need to really understand if you have a transport protein deficiency.