Functional Markers of Vitamin B12 Metabolism in Modern Laboratory Diagnostics

Abstract

Traditional laboratory evaluation of the total serum cobalamin pool is characterized by low diagnostic specificity, frequently masking profound intracellular vitamin B12 deficiency amidst borderline or falsely normal analytical metrics. This study investigates the diagnostic and prognostic efficacy of functional metabolic markers—holotranscobalamin (HoloTC), methylmalonic acid (MMA), and homocysteine (Hcy)—in verifying true tissue cobalamin deficiency. Within a prospective observational framework, the clinico-laboratory parameters of 215 patients presenting with neurological and hematological symptomatology underwent comprehensive biochemical screening utilizing electrochemiluminescence immunoassay (ECLIA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Mathematical modeling and logistic regression analysis exposed a phenomenon of metabolic discordance: 42.3% of patients exhibiting clinical polyneuropathy possessed total vitamin B12 levels within the reference range (220-400 pg/mL), whereas active HoloTC concentrations were critically depleted (< 35 pmol/L), accompanied by pathological MMA accumulation (> 0.45 µmol/L). Multivariate evaluation of ROC curves demonstrated the absolute analytical superiority of the integrated "HoloTC + MMA" panel (AUC 0.942, sensitivity 91.5%, specificity 88.4%) over isolated total cobalamin measurement (AUC 0.654). The acquired data substantiate the urgent necessity to revise routine diagnostic algorithms. Implementing the assessment of active fractions and cobalamin metabolites minimizes the risk of diagnostic errors, prevents the progression of irreversible demyelinating processes, and facilitates precise patient stratification for targeted replacement therapy.