Table 1.

Overview of iron deficiency parameters.

Parameter	Elevated	Reduced	Shows	Disadvantages
Serum Iron	Iron overload (preanalytical hemolysis)	Iron deficiency and acute/chronic inflammation	Amount of iron (Iron bound to transferrin & non-transferrin bound iron)	High intra- and inter-individual variability Neither sensitive nor specific
Ferritin	Acute phase, liver disease, lymphoma	Iron deficiency with depleted iron storage	Iron stores	Acute phase reactant, no direct conclusion for erythropoiesis
Transferrin	Iron deficiency, pregnancy (last trimester)	Chronic inflammation, tumors, hemolysis	Transport iron, demand by erythropoiesis	By itself only indicates demand, not supply
Transferrin saturation	Iron overload	Iron deficiency, acute phase, pregnancy (last trimester)	Percentage of filled transferrin binding sites	Acute phase reactant, requires two measurements (transferrin, iron)
Soluble transferrin receptor	Increased erythropoiesis during iron deficiency	Chronic kidney disease with reduced EPO	Secreted fragment of transferrin receptor	Not elevated during acute phase, reference interval highly dependent on specific test, expensive
Transferrin receptor	Iron overload	Iron deficiency, acute phase, pregnancy (last trimester)	Target of transferrin iron transport, mediates iron uptake by endocytosis	Acute phase reactant
sTfR-Ferritin index	Iron deficiency	Anemia of chronic disease	sTfR/log Ferritin	Requires two measurements, thus complex and costly
Hepcidin	Iron deficiency anemia, CKD, inflammation	Iron overload	Iron absorption and release from storage	Complex measuring methods, reference interval highly dependent on specific technology
RET-He		Iron deficient erythropoiesis	Functional availability of iron	Not available from all manufacturers

CKD = chronic kidney disease; EPO = erythropoietin; sTfR = soluble transferrin receptor; Ret-H_e = mean reticulocyte hemoglobin.