One of two working forms of vitamin B12, the only one active inside the cell's energy compartments. That it corrects a shortfall and the blood and nerve problems that follow is well established; that the ready-made form beats the manufactured one is not. Harm signals cluster in folic-acid combinations, men who smoke, and diabetic kidney disease. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Serum vitamin B12 (total cobalamin) | 500–900 pg/mL | Confirms the supplement is reaching the bloodstream |
| Methylmalonic acid | Below 0.27 µmol/L | The direct functional readout of the adenosylcobalamin-dependent reaction |
| Holotranscobalamin (holoTC) | Above 50 pmol/L | Measures the fraction of cobalamin actually deliverable to cells |
| Homocysteine | Below 9 µmol/L | Tracks the cytosolic arm of cobalamin metabolism |
| Serum folate | 10–20 ng/mL | Prevents misreading a combined shortfall and flags over-supplementation |
| Complete blood count with mean corpuscular volume (MCV) | MCV 82–90 fL | Detects the enlarged red cells of cobalamin deficiency and their correction |
| Ferritin | 50–150 ng/mL | Rules out the iron deficiency that masks cobalamin-driven cell enlargement |
| Serum potassium | 4.0–4.5 mmol/L | Catches the transient fall that accompanies rapid correction of severe anaemia |
| Creatinine with estimated glomerular filtration rate (eGFR) | eGFR above 90 mL/min/1.73 m² | Required to interpret methylmalonic acid and to identify the DIVINe risk group |
Cadence: Baseline, then a recheck at 8–12 weeks, then at 6 months, then every 6–12 months indefinitely