Pathophysiology
Clinical meaning
The NP must master the iron studies panel as an integrated diagnostic tool rather than interpreting individual values in isolation. The core iron panel includes serum iron, total iron binding capacity (TIBC), transferrin saturation (TSAT), and serum ferritin, each reflecting different aspects of iron metabolism. Serum iron measures the concentration of iron bound to transferrin in the plasma at the time of sampling; it has significant diurnal variation (highest in the morning, lowest in the evening with a 30-50% swing), is acutely affected by recent iron intake, and drops rapidly during acute infection or inflammation as part of the innate immune response to sequester iron from pathogens. TIBC is an indirect measure of transferrin concentration in the serum: since each transferrin molecule binds two iron atoms, TIBC reflects the total plasma iron-carrying capacity. The liver regulates transferrin synthesis inversely to iron stores -- in iron deficiency, the liver upregulates transferrin production (increasing TIBC) to maximize iron scavenging; in iron overload, transferrin synthesis decreases (decreasing TIBC). Transferrin saturation (TSAT) is calculated as (serum iron / TIBC) x 100 and represents the...