Holo TC Assay - jimmylegs….do you know?

[christobelle]

Hi all, but in particular jimmy legs with your super knowledge!!!

I just got my levels back for the transcobalamin - Holo TC Assay.

Do you know much about what these mean?? My level was 40 pmol/L

Thanks very much

[jimmylegs]

hi here's some relevant info

Screening for metabolic vitamin B12 deficiency by holotranscobalamin in patients suspected of vitamin B12 deficiency: a multicentre study
http://acb.sagepub.com/content/49/2/184.short
Critical evaluation of cut-off values of holoTC indicated that a cut-off value of 32 pmol/L can be considered in screening for metabolic vitamin B12 deficiency (defined by MMA > 0.45μmol/L) in a mixed patient population.

also:

Holo-transcobalamin is an indicator of vitamin B-12 absorption in healthy adults with adequate vitamin B-12 status
http://ajcn.nutrition.org/content/85/4/1057.full
...The three 9-μg vitamin dose sequence used in this study has previously been chosen to minimize passive absorption and to maximize the amount of actively absorbed vitamin B-12 (17, 18). This aspect of the protocol would be important in a clinical vitamin B-12 absorption test, because it is the capacity to actively absorb vitamin B-12 that is being assessed. Further studies evaluating the necessity of 3 doses and the exact timing of the doses are warranted.

Studies of biomarker responses to intervention with vitamin B-12: a systematic review of randomized controlled trials
http://www.ncbi.nlm.nih.gov/pubmed/19403638
The available evidence suggests that plasma and serum concentrations of total vitamin B-12, methylmalonic acid, and total homocysteine are all effective biomarkers of a change in vitamin B-12 intake; however, because the available data were limited, it was not possible to examine fully the factors that could explain the substantial heterogeneity in total vitamin B-12. Future trials should include low-dose vitamin B-12 in adults across the entire age spectrum and measure the holotranscobalamin response to supplementation.

Holotranscobalamin, a marker of vitamin B-12 status: analytical aspects and clinical utility
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3127504/
A major concern has been the possible elevation in holoTC after intake of vitamin B-12–rich food. The few studies that have addressed this issue have shown very limited variations related to intake of a normal diet (9, 29) and because of that, blood can be drawn both from fasting and nonfasting individuals. However, repeated intakes of high physiologic doses of vitamin B-12 (eg, 9 μg 3 times in 1 d) elevate the holoTC concentration (and to a lesser degree the total vitamin B-12 concentration) within 24 h (30).

[christobelle]

Thanks very much for all that info.

Reading through it seems my 40 reading combined with the 283 B12 means it isn't classified as deficient, even though it doesn't hit the 400 or 500 mark for the B12 itself. That is how I understood from the reading.

So much information to digest. I'm not quite sure I will ever get to the level of actual comprehension lol!!

[jimmylegs]

it's an interesting one. although 500 has been proposed as a cutoff to prevent cognitive deficits, and although it is true that serum lower cutoffs are associated more with hematological than cognitive criteria, when i apply the same approach to b12 as i have with other essential nutrients, i don't find that healthy control groups consistently have serum levels above 500. it's definitely a mix.

since optimizing my cofactors, eating a balanced diet including b12-rich foods, and reducing nutrient-draining foods, plus taking a daily multi, my serum b12 seems to have been floating around the high 400s. so, i'm comfortable with it being there

i haven't had enough time looking at studies on holo tc to really evaluate whether hcy and mma effects are the only relevant markers of concern when it comes to b12, or if those are just the latest thing!