The effect of burosumab on intact and C‐terminal FGF23 measurements

Abstract

This article describes a negative analytical interference by burosumab in an intact FGF23 immunoassay. The recovery of C-terminal FGF23 is not significantly affected by the presence of burosumab. In vivo, both assays demonstrate extreme FGF23 elevations in the presence of the drug. Furthermore, the measurement of FGF23 blocked by burosumab is not clinically useful regarding hypophosphataemia.