Growth Differentiation Factor-15 (GDF-15) is a stress-responsive cytokine belonging to the Transforming Growth Factor-beta (TGF-β) superfamily. Initially identified as macrophage inhibitory cytokine-1 (MIC-1), GDF-15 is expressed in various tissues and markedly upregulated under pathological conditions involving inflammation, oxidative stress, and tissue injury. Notably, GDF-15 upregulation has been associated with several cardiovascular events, such as heart failure, atrial fibrillation, atherosclerosis, coronary artery disease, and stroke. Furthermore, it has been observed that GDF-15, either alone or in combination with other cardiac biomarkers, can provide valuable complementary information enhancing risk assessment, early detection of cardiovascular events, and prediction of adverse outcomes. GDF-15 can be measured in various body fluids, using different methods. Immunoassays are widely employed and offer good sensitivity and reproducibility; however, variability between methods and potential interference from genetic variants highlight the need for standardization. This review summarizes current insights into GDF-15, with emphasis on its quantification methods, biological functions in cardiovascular diseases, and its emerging role as a diagnostic and prognostic biomarker.

Vitamin B12 is an essential water-soluble vitamin required for critical biological processes such as DNA synthesis, erythrocyte maturation, and maintenance of nervous system integrity. Deficiency of vitamin B12 can lead to serious clinical outcomes, including megaloblastic anemia, and potentially irreversible neurological damage. Conversely, hypercobalaminemia may be associated with severe disorders, including solid neoplasms, hematological malignancies and, in some cases, may result from inappropriate supplementation or immunoglobulin–B12 macro-complexes. Although current guidelines recommend total serum vitamin B12 and holotranscobalamin (holoTC) as first-line biomarkers, total serum vitamin B12 remains the most widely used test in routine clinical practice. However, since holoTC represents the biologically active fraction of vitamin B12 available for receptor-mediated cellular uptake, it appears to provide a more reliable assessment of cobalamin status, particularly in specific clinical contexts. Compared with total vitamin B12 measurement, holoTC is assessed using a more limited number of analytical methods and the majority of available kit are aligned with the WHO reference standard, thereby improving inter-assay harmonization. This review explores literature data about the role of vitamin B12 and holoTC, discussing analytical challenges and clinical interpretation, highlights the potential advantages of holoTC over total serum B12.

Background: Vitamin B12 is an essential water-soluble vitamin required for critical biological processes such as DNA synthesis, erythrocyte maturation, and maintenance of nervous system integrity. Deficiency of vitamin B12 can lead to serious clinical outcomes, including megaloblastic anemia and potentially irreversible neurological damage. Conversely, hypercobalaminemia may be associated with severe disorders, including solid neoplasms and hematological malignancies, or may result from inappropriate supplementation or immunoglobulin–B12 macrocomplexes. Current guidelines recommend total serum vitamin B12 and holotranscobalamin (holoTC) as first-line biomarkers for assessing cobalamin status. Content: Despite guideline recommendations, total serum vitamin B12 remains the most widely used test in routine clinical practice. However, holoTC represents the biologically active fraction of vitamin B12 available for receptor-mediated cellular uptake and may therefore provide a more reliable assessment of cobalamin status, particularly in specific clinical settings. Compared with total vitamin B12 measurement, holoTC is evaluated using a more limited number of analytical methods, and most commercially available assays are traceable to the WHO reference standard, improving interassay harmonization. This review examines the role of vitamin B12 and holoTC, focusing on analytical challenges and clinical interpretation. Summary: The available evidence suggests that holoTC may offer important advantages over total serum vitamin B12 in the evaluation of B12 status. Its biological relevance and improved analytical harmonization support its potential utility as a more reliable biomarker in selected clinical contexts.