AB0720 SOLUBLE TRANSFERRIN RECEPTOR IN DIAGNOSIS OF IRON DEFICIENCY ANEMIA IN PATIENTS WITH SPONDYLOARTHRITIS
Authors: K. Safarova, A. Rebrov
Journal: Annals of the Rheumatic Diseases (2020)

Background: Anemia is a frequent hematological disorder in patients with rheumatic diseases. The main pathogenetic variants of anemia are anemia of chronic disease (ACD), iron deficiency anemia (IDA), and anemia of chronic disease with iron deficiency (ACD/IDA). The presence of systemic inflammation hinders to diagnose absolute iron deficiency, because standard tests of iron status are affected by it. Soluble transferrin receptors (sTfR) measurement and the calculation of the sTfR/ log ferritin index (sTfR index) are recommended, but data about diagnostically significant levels of these indicators in patients with spondyloarthritis (SpA) is currently limited. Objectives: To assess the diagnostic significance of sTfR and the sTfR index for detecting absolute iron deficiency in patients with SpA and anemia. Methods: Complete blood count, standart iron metabolism parameters, C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) were evaluated in 68 patients with SpA. Serum concentration of sTfR was measured with enzyme-linked immunosorbent assay (ELISA) using sTfR ELISA kit («Monobind Inc.», USA). The sTfR index was calculated by the formula sTfR/log 10 ferritin. Anemia was defined using the World Health Organization criteria. Depending on the serum ferritin concentration, transferrin saturation, and CRP level, ACD, IDA, or combined anemia (ACD/IDA) were diagnosed. Disease activity was determined by the BASDAI (Bath Ankylosing Spondylitis Disease Activity Index) and ASDAS-CRP (Ankylosing Spondylitis Disease Activity Score based on CRP) scales. Receiver operating characteristic (ROC) analysis was performed with MedCalc. Results: Anemia was found in 48 of 68 (70,6%) SpA patients. 16 (33,3%) patients had ACD and 32 (66,7%) had ACD/IDA. Hemoglobin level in ACD was 118 [112; 123] g/L, in ACD/IDA – 110 [106; 120] g/L, in non-anemic patients – 133 [129; 145] g/L (p&lt;0.001 for all groups). CRP and ESR values were higher in ACD compared to ACD/IDA patients (31.5 [20.3; 46.4] mg/L and 27.0 [16.0; 35.5] mm/h versus 9.8 [5.6; 16.9] mg/L and 15.5 [12.0; 22.5] mm/h, respectively [p=0.00 and p=0.038]). No statistically significant difference was found between all groups in BASDAI and ASDAS-CRP scores. ACD/IDA patients had significant increases in serum sTfR levels (1.7 [1.4; 2.2] mg/L) compared to ACD (1.5 [1.1; 1.7] mg/L, p=0,04) and to non-anemic patients (1,3 [1,1; 1,6] mg/L, p=0,003). The sTfR index was significantly higher in ACD/IDA (0.93 [0.82; 1.24]) compared to patients with ACD (0.64 [0.48; 0.75], p&lt;0.001) and without anemia (0.67 [0.56; 0.81], p&lt;0.001). The areas under the curves (AUCs) for distinguishing between ACD/IDA and ACD were 0.85 for sTfR index (p&lt;0,001), 0.72 for sTfR (p&lt;0,001). The sTfR index (cutoff &gt;0.83) and sTfR (cutoff &gt;1.39 mg/L) had sensitivities of 75% and 53%, and specificities of 83% and 81%, respectively. Conclusion: According to obtained data, serum concentration of sTfR &gt;1.39 mg/L and the sTfR index &gt;0.83 point to the presence of iron deficiency component in the structure of anemic syndrome in patients with SpA. References: Management of patients with SpA requires constant monitoring of side effects of therapy, in particular induced by the non-steroidal anti-inflammatory drugs. Use of sTfR and the sTfR index can improve the detection of IDA. A significant advantage of these indicators is their independence from systemic inflammation. Disclosure of Interests: None declared