Железосвязывающая способность сыворотки общая (ОЖСС, TBIС)

Total iron-binding capacity (TIBC), also called serum iron-binding capacity, assesses the amount of iron that circulating transferrin can bind. The test is typically ordered with serum iron, unsaturated iron-binding capacity (UIBC), and transferrin to calculate transferrin saturation and to characterize iron status. It supports evaluation of anemia by helping distinguish iron deficiency from alternative etiologies such as anemia of chronic disease or vitamin B12 deficiency. TIBC also contributes to the assessment of iron excess; in iron deficiency, serum iron decreases and TIBC increases, whereas in acute iron exposure or hereditary hemochromatosis, serum iron increases and TIBC is decreased or within the reference interval.

Iron is an essential trace element incorporated into hemoglobin within erythrocytes, enabling oxygen transport, and into myoglobin and numerous enzymes. Dietary iron is absorbed in the gastrointestinal tract and circulates bound to transferrin, a transport protein synthesized in the liver. The human body contains approximately 4–5 g of iron, with about 3–4 mg (approximately 0.1% of total body iron) circulating in plasma bound to transferrin. Transferrin concentration is influenced by hepatic function and nutritional status. Under physiological conditions, roughly one third of transferrin binding sites are occupied by iron, leaving the remainder available for binding. TIBC is determined by adding a defined amount of iron to serum in vitro to saturate available transferrin binding sites and then measuring the iron bound to transferrin; the result reflects the serum transferrin concentration. In iron deficiency, hepatic synthesis of transferrin increases, leading to a higher TIBC and expansion of the unsaturated iron-binding capacity. In iron excess, most transferrin binding sites are occupied, so the unsaturated fraction decreases and TIBC is reduced or remains within the reference interval. Although serum iron exhibits notable diurnal and day-to-day variability—most prominently in the morning—TIBC remains relatively stable.