Chronic Renal Failure and Calcium Unlike primary hyperparathyroidism, in which the parathyroid glands function autonomously and lead to a high total serum calcium level secondary to increased production of calcitriol and calcium absorption from the gut. Total calcium concentrations with renal secondary hyperparathyroidism can be normal, elevated, or low (Nelson RW & Feldman EC,2004). Studies looking at calcium concentrations in dogs with CRF have mainly focused on the total calcium concentration. Hypercalcemia, based on total calcium levels, has been observed in approximately 10% of dogs with CRF, and the prevalence appears to increase with the severity of azotemia (Schenck PA, et al.,2006). The phosphate theory of renal secondary hyperparathyroidism. With chronic renal disease, a decreased glomerular filtration rate (gFr) leads to an increased serum phosphate concentration and a decreased Calcium level, which stimulates the release of PTH (Chew DJ,1990).