Soluble transferrin receptor (sTfR) is a biochemical parameter used for the detection of iron deficiency in situations where ferritin has limited diagnostic value owing to the present chronic disease. The sTfR concentration was determined in 118 patients divided according to their inflammatory status and underlying disease into groups of patients with iron-deficiency anemia (IDA), anemia of chronic disease (ACD) and patients with a coexisting state of iron deficiency and anemia of chronic disease (ID+ACD). All patients with iron deficiency had elevated sTfR levels, but ferritin concentrations were normal or increased in patients with inflammatory characteristics. Diagnostic efficiencies of sTfR, sTfR/log ferritin index (sTfR/F) and ferritin were evaluated by receiver operating characteristic curve (ROC) analysis. According to the results obtained, the best diagnostic efficiency for differential diagnosis of anemic patients with iron deficiency compared to the control group had a sTfR concentration (0.884) that was significantly higher than ferritin (0.638), but not higher than the calculated ratio sTfR/F (0.820). The cut-off value of the sTfR/F index differentiating the best control group from the IDA and ID+ACD groups was 1.30, and for differentiation of ACD from IDA and ID+ACD, the value was 0.90. Soluble transferrin receptor is an additional parameter to ferritin for the diagnosis of IDA and differential diagnosis of ID+ACD, but calculation of the sTfR/F index did not improve the diagnostic value of determining sTfR alone.