Background During last years, the great attention is paid to the identification of biomarkers which can help in differentiating the type of arthritis. The recent studies have shown Adenosine deaminase (ADA) can be useful in this regards . ADA, an enzyme of purine metabolism, catalyses the irreversible deamination of (deoxy)adenosine to (deoxy)inosine. It plays a significant role in the immune system . The enzyme is released into synovial fluid followed by significant elevation of its activity during inflammatory joint disorders such as rheumatoid arthritis (RA). Endogenous adenosine, a substrate of ADA, is provided with tissue protective property against damages. It’s anti-inflammatory effect is conditioned by decreasing the level of pro-inflammatory cytokines, increasing the level of anti-inflammatory cytokines, cytokine modulation of macrophage and monocytes and regulation of endothelial cell inflammatory functions. Therefore, ADA can help in understanding some pathologic aspects of diseases, in relieving the triggering factors of inflammation and promoting a new diagnostic approach.
Objectives The goals of this work were to compare the levels of ADA activity in synovial fluid of patients with RA and osteoarthritis (OA), to determine the proper cut-off level for ADA in differentiating of RA and OA, to calculate the sensitivity and specificity of ADA-test.
Methods The study involved 40 patients (23 - with RA and 17- with OA). They were diagnosed according to the accepted classification criteria of diseases. Synovial fluid samples obtained from patients and stored at -20°C, were refrozen, centrifuged, diluted three times and the aliquots were taken for the enzyme assay. The ADA activity was assayed by evaluation of ammonia amount, liberated in the reaction of adenosine deamination, using a phenol-hypochlorite colorimetric method. Statistical analyses were performed with GraphPad software, version 3, for Windows (USA). Unpaired two-tailed t-test with Welch correction was applied.
Results The obtained mean values of ADA activity were 33.9 ± 22.4 (mean ± SD) IU/L (maximum – 99.6, minimum – 10.5) in RA patients and 4.6 ± 3.99 (mean ± SD) IU/L (maximum - 12.7, minimum - 0.3) in OA patients. They evidence statistically significant difference (p < 0.0001) between ADA levels in joint synovial fluid in RA and OA patients. The optimal cut-off value of ADA activity for differentiating these diseases was evaluated using ROC curve method as 12 IU/l. Based on this value, for ADA test, the sensitivity (the ratio of positive diagnoses - 22, to the sum of this number and the number of false negative diagnoses - 1), was 96%, the specificity (the ratio of negative diagnoses - 15, to the sum of this number and the number of the false positive diagnoses - 2), was 88%.
Conclusions In spite of limited number of studied samples, the obtained data on ADA activity are statistically significant and evidence the high specificity and sensitivity of the test. However, it requires further study on a larger number of patients with inflammatory and degenerative diseases of joints.
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Disclosure of Interest None Declared
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