Low Active B12
Low Active B12 indicates functional vitamin B12 deficiency, meaning insufficient biologically available B12 for cellular use. B12 deficiency can lead to anaemia, neurological symptoms (such as neuropathy, memory problems, and confusion), fatigue, muscle weakness, and mood changes, some of which may become irreversible if untreated. Thus, low Active B12 is clinically significant and warrants treatment to prevent progression to deficiency anaemia and neurological damage.

High Active B12
A high Active B12 level is less clinically significant and is not associated with toxicity. Elevated levels may occur through supplementation or reflect increased transport proteins. A high B12 is not identified as a clinical disorder, and raised levels alone do not indicate deficiency or disease.