Table 5.
Mean VB12/MMA and plasma tHCY levels and % VB12-deficient patients according to different criteria.
| Characteristic | Number (% Total) |
|---|---|
| A. Single serum measurements [VB12, MMA, and tHCY] | |
| I. VB12 levels | |
| Ia. VB12 level (pg/mL) | |
| Mean ± SEM | 394 ± 14 |
| (range) | (71–999) |
| Ib. Proposed VB12 deficiency | |
| # with VB12 level < 200 pg/mL (a) | 18 (10%) |
| # with VB12 level 200–350 pg/mL (b) | 67 (38%) |
| II. MMA levels | |
| IIa. MMA value (uM) | |
| Mean ± SEM | 0.25 ± 0.01 |
| (range) | (0.06–0.83) |
| IIb. Proposed VB12 deficiency < 200 pg/mL (c) | |
| # with MMA level > 0.26 (uM) (a) | 53 (30%) |
| # with MMA level > 0.37 (uM) (b) | 32 (18%) |
| IIII. Plasma tHCY levels | |
| IIIa. tHCY value (uM) | |
| Mean ± SEM | 10.20 ± 0.41 |
| (range) | (4.0–47) |
| IIIb. Proposed VB12 deficiency (d) | |
| # with tHCY level > 13 uM (a) | 22 (13%) |
| # with tHCY level > 15 uM (a) | 14 (8%) |
| B. Combination blood measurements [VB12, MMA, and tHCY] | |
| # with VB12 level < 200 pg./mL + MMA > 0.37 uM (e) | 14 (8%) |
| # with VB12 level < 200 pg./mL + tHCY > 15 uM (e) | 8 (4.6%) |
| # with MMA level > 0.37 uM or tHCY > 15 uM and response to VB12 administration [normal folate] (f) | 37 (21%) |
Abbreviations: MMA—serum methylmalonic acid level; tHCY—plasma total homocysteine level; and VB12 level: serum vitamin B12 concentration. (a) Numerous studies have proposed a serum VB12 level of <200 pg/mL for diagnosing VB12-deficient patients [112,113,114,115,118,120,233,235]. (b) Serum VB12 levels over the range of 200–350 pg/mL have been reported to represent a low-level range that could suggest VB12 deficiency [115,116,118]. (c) Many studies propose that an MMA level > 0.37 uM should be generally used to identify VB12-deficient patients [115,116,117,118] and a few recommend using an MMA level of >0.26 uM [116,235,236,237]. These recommendations are only for patients with normal renal function [113,116,236,238]. (d) Various studies have proposed either a tHCY level of >13 uM [113,115,234] or >15 uM [112,114,115,235] as the upper limit of normal. (e) Numerous combinations of serum VB12 levels with either MMA or tHCY levels have been reported to be more sensitive than either one alone [112,113,114,115,119,120]. (f) The response of blood MMA/tHCY with normal serum folate levels and renal function to the administration of crystalline VB12 either given orally or parenterally is considered by many to be one of the single best measurements of VB12 deficiency [112,114,117,236,237].