Background:Fibroblast growth factor 23 (FGF23) levels are elevated in cardiopulmonary bypass (CPB)-associated acute kidney injury (AKI); however, it is unknown how much of the circulating FGF23 is intact and bioactive. Hypoxia may induce FGF23 production, yet its impact in humans is unknown. Pediatric cardiac surgery patients have both a high incidence of CPB-associated AKI and a high prevalence of chronic hypoxemia. Methods:We assessed the effects of hypoxemia and CPB-associated AKI on C-terminal FGF23 (cFGF23) and intact FGF23 (iFGF23) levels in 32 pediatric cardiac surgery patients with normal eGFR. Plasma cFGF23 and iFGF23 were measured pre-operatively and serially post-operatively. Results:Despite normal renal and ventricular function, pre-operative cFGF23 levels were high and elevated out of proportion to iFGF23 levels. Pre-operative oxygen saturation correlated inversely with FGF23. Pre-operative cFGF23 and oxygen saturation both predicted post-operative AKI. Post-operatively, cFGF23 and iFGF23 increased early post-reperfusion; although cFGF23 levels remained elevated, iFGF23 levels soon returned to baseline.Conclusions:Pre-operative cFGF23 may predict CPB-associated kidney dysfunction. Changes over time in cFGF23 and iFGF23 levels post-CPB differ. Chronic hypoxemia may affect FGF23 production in humans
