Albertine Donker

TSAT/Hepcidin Ratio discriminates TMPRSS6 -related Anemia from IDA 289 8 DISCUSSION In this study we aimed to (i) validate the TSAT/hepcidin ratio as a diagnostic tool to distinguish TMPRSS6- related IRIDA from other disorders presenting with IDA unrelated to TMPRSS6 and (ii) to establish a cutt-off value for the ratio to differentiate between both groups with high specificity. Using standardized hepcidin values, we confirmed that the TSAT/hepcidin ratio is able to distinguish IRIDA patients from IDA controls in a broad iron deficient population, provided moderate or severe inflammation is absent and no recent iron therapy has been given. Based on our findings, we reasoned that using our standardized hepcidin assay a ratio of 5.9%/nM or lower strongly indicates the presence of IRIDA, as a low TSAT/hepcidin ratio was highly specific for TMPRSS6- related IRIDA. To our knowledge, there is only one research group that elaborated a comparable biochemical method to distinguish IRIDA from other forms of IDA. Heeney et a l 13 evaluated the TSAT/log 10 (hepcidin) ratio to predict which patients were most likely to have bi-allelic TMPRSS6 mutations in a group of patients who had a high pre-test probability of having IRIDA, as they had chronic iron deficiency with TSAT≤15% and a poor response to at least one course of oral iron supplementation. After genetic evaluation of TMPRSS6 , they included for further analysis 44 patients with bi-allelic TMPRSS6 defects and 59 IDA controls without identifiable TMPRSS6 mutations by Sanger sequencing. In agreement with their observations, 13 we also found that hepcidin levels were significantly higher in TMPRSS6 -related IRIDA patients compared to IDA controls. Moreover, while Heeney et al apply the TSAT/log 10 (hepcidin), we observed better ROC characteristics with higher specificity using the TSAT/hepcidin ratio, to distinguish IRIDA patients from IDA controls. A higher pre-test probability of having TMPRSS6 -related IRIDA in the study population of Heeney et al might explain the difference in ROC characteristics, since they included IDA patients that failed to respond to oral iron supplementation, while we did not test responsiveness to oral iron in our IDA controls. 38 In addition, we argue that our IDA controls might have been more iron deficient compared to Heeney’s et al controls, resulting in lower hepcidin levels and that recent iron therapy could have increased hepcidin levels in their study population.