[Biochemical markers of iron status]

Traditionally, the standard biochemical markers of iron status are serum iron, transferrin, transferrin saturation, ferritin and, more recently, soluble transferrin receptor. Diagnosis of iron deficiency is usually associated with a low serum ferritin concentration. The diagnosis can be difficult in diseases in which there is an acute-phase response, because ferritin is an acute-phase reactant. In this case, measuring soluble transferrin receptor may be useful because an increased concentration is an indicator of iron deficiency. Iron stores are frequently diminished in patients on dialysis, as a result of increased blood loss and poor iron absorption. Demand for available iron is increased further by the use of erythropoietin and iron deficiency is one of the primary causes for decreased response to recombinant human erythropoeitin therapy (rHuEpo). Prevalence of inflammation in patients on dialysis is estimated to be high (as 50% patients). Because ferritin is an acute-phase reactant, levels may be elevated in cases of inflammation. The aim of recent guidelines is to better assess anaemia and iron stores. Serum ferritin and transferrin saturation are regarded as the most reliable indicators of iron status. A newer alternative laboratory measurement is the soluble transferrin receptor. Some authors suggest that the circulating soluble transferring receptor levels may be useful in monitoring iron status in patients on dialysis if rHuEpo doses are maintained constant. Prospective longitudinal studies are needed to evaluate this hypothesis.