Other factors that were not studied could contribute to changes in TmP/GFR such as: variations in growth hormone or cortisol,(36, 37) iron deficiency,(38) iron infusions,(39, 40) and nicotinamide phosphoribosyltransferase.(41) Third, physiologic fluctuation of TmP/GFR may explain the fall in TmP/GFR after PTH1‐34, but the degree of lowering at 58%, in conjunction with changes in both NcAMP and bone turnover markers, would be difficult to explain as a chance occurrence. Here, GH1 is linked to Iron deficiency anemia.