Inclusion and exclusion criteria: Patients examined in our outpatient clinic for further work-up of presumed kidney damage were evaluated prospectively as previously published to examine the link between selenoprotein P, thyroid hormone, and renal impairment [28]. Thus, serum samples were drawn from July 2013 to July 2014. After centrifugation, serum samples were stored frozen (−80°) and analyzed between August 2014 and October 2014.

Reasons for study exclusion were previous known thyroid disorder requiring thionamides or levothyroxine treatment, and/or presence of antibodies against thyroid peroxidase, as well as medication with known or potential influence on thyroid hormone function (current or past intake of amiodarone, a high-dose steroid or furosemide, anticonvulsives, heparin, or estrogen-replacement therapy). Our local ethics committee approved the study. All patients gave informed consent to undergo testing and to be included in this pseudonymized analysis.