Diagnostic challenge of high vitamin B12 levels: a case report and review of the literature

Vitamin B12 (cobalamin) deficiency is a well-documented clinical condition, with several causes and important consequences. High serum B12 level (hypercobalaminemia) is less common and not easily explained, being caused by different conditions, such as blood disorders, autoimmune diseases, and solid tumors. Moreover, cases of increased B12 levels due to the presence of polymers formed by vitamin B12 and other proteins have been described to show falsely elevated serum levels when measured by conventional methods. A 47-year-old white Italian man presented to an internal medicine ward complaining a sensation of a swollen tongue and upper limb paresthesias. Laboratory tests showed an increased level of cobalamin in the blood (6173 pg/ml); excessive cobalamin intake, solid tumors, autoimmune diseases, and hematological disorders were excluded. The use of polyethylene glycole precipitation allowed for the detection of macro-B12, a polymer composed of B12 and high-molecular-weight proteins, such as antibodies. The true value of vitamin b12 in the blood of our patients was normal. High serum B12 levels may be due to a wide range of conditions, including severe diseases; when high levels of vitamin B12 are detected, it is useful to perform a screening for the most well-known conditions associated with this finding. The use of methods such as polyethylene glycole precipitation consent to identify the possible presence of a macro-B12.