Soluble transferrin receptors and ferritin index in the diagnosis of iron deficiency in patients with spondyloarthritis and anemia

Aim. To assess the diagnostic value of the detection of soluble transferrin receptors (sTfR) and ferritin index (sTfR/log Fer) in patients with spondyloarthritis (SpA) and anemia for the revealing absolute iron deficiency (ID). Materials and methods. The study included 68 patients with SpA: median age 39 [34; 47] years, men: 38 (55.9%). Hemogram, C-reactive protein levels and ferrokinetics parameters were assessed, including sTfR testing by the method of quantitative enzyme-linked immunosorbent assay (Monobind Inc., USA). We also calculated sTfR/log Fer. Based on ferrokinetics parameters and C-reactive protein levels, chronic disease anemia (CDA), iron deficiency anemia (IDA), or their combination (CDA/IDA) were diagnosed. Results. CDA was diagnosed in 16 patients, CDA/IDA in 32 patients, and 20 patients had no anemia. An increase in sTfR concentration in patients with CDA/IDA (1.7 [1.4; 2.2] mg/L) compared with patients with CDA (1.5 [1.1; 1.7] mg/L, p0.05) was revealed. sTfR/log Fer in patients with CDA/IDA (0.93 [0.82; 1.24]) was higher than in patients with CDA (0.64 [0.48; 0.75], p0.0001). When evaluating the ROC curves, it was found that sTfR levels 1.39 mg/L and sTfR/log Fer levels 0.83 indicate the presence of absolute ID. The area under the ROC curve for sTfR was 0.72 (95% confidence interval 0.600.82, p0.001), for sTfR/log Fer 0.85 (95% confidence interval 0.740.92, p0.001). The sensitivity and specificity of sTfR/log Fer (75 and 83%, respectively) were higher compared with sTfR (53 and 81%, respectively). Conclusion. In patients with SpA having CDA/IDA, sTfR and sTfR/log Fer are statistically significantly increased. The results obtained indicate the possibility of diagnosing ID by using these parameters.