In a different study in dogs, mean calcitriol concentrations were lower in the CKD group compared to healthy dogs even at early stages.145 The decrement of calcidiol was considerably more prominent than the decrease in calcitriol.154 It is not surprising that calcitriol was not suppressed below the reference interval due to the correcting effects explained by the calcitriol trade-off hypothesis in which increased PTH promotes more renal synthesis of calcitriol. Here, PTH is linked to chronic kidney disease.