FGF23 and atrial fibrillation: For example, we have previously shown that ICTP and gal-3 have lower intra-cardiac than peripheral levels, with no significant difference in the cases of FGF-23 and PIIINP.[9] Therefore, it appears that if any AF-related cardiac processes are indeed causing release of these biomarkers into the bloodstream, systemic fibrosis masks this in peripheral blood.