In clinical practice, for the diagnosis of iron deficiency (ID), doctors use markers whose level changes in the presence of a systemic inflammatory process: ferritin, iron and transferrin saturation with iron. Soluble transferrin receptor (sTFR) is the only marker of ID, the content of which does not depend on the pathogenetic mechanisms of inflammation. Due to the fact that ferritin reflects iron stores in the body, and sTFR — its functional need, for the diagnosis of ID it is also recommended to use the index sTFR/log Ferritin (index sTFR-F). The purpose of this study is to assess the diagnostic value of determining the serum level of sTFR, as well as the index sTFR/log Ferritin in identifying the true ID in the background of anemias of various origins. We analyzed the sTFR level and the index sTFR-F in the blood of 106 patients with anemia. In the group of ID anemia, the level of sTFR was significantly higher compared with the control group and comparison groups. During the ROC analysis, the sensitivity of sTFR was 91.7%, the specificity was 86.8%, and the sensitivity and specificity of the index sTFR-F were 89.2% and 92.9%, respectively.