β-Trace protein (BTP) is a low-molecular-weight glycoprotein with multiple isoforms of varying molecular weight (23-29kDa) and an emerging marker of glomerular filtration rate (GFR).1,2 Equations for estimated GFR (eGFR) that incorporate BTP have been proposed.1,3 As of 2013, assays for BTP in biological fluids were commercially available from Cayman Chemicals (an immunometric ELISA using monoclonal murine antibodies4) and Siemens (a particle-enhanced nephelometric immunoassay using polyclonal rabbit antibodies against human urinary BTP5).