Primary hyperparathyroidism (PHPT) is the most common etiology of hypercalcemia in the ambulatory setting and usually presents with an intact parathyroid hormone (PTH) level that is elevated or inappropriately near the upper limit of the laboratory reference range. However, PHPT with low-normal PTH level is reported in the peer-reviewed literature, and this atypical presentation may delay diagnosis of PHPT. We present a case of PHPT with persistently low-normal PTH level in which the PTH dependence of hypercalcemia was demonstrated by the response to treatment with the calcimimetic agent cinacalcet.

Chronic Kidney Disease-Mineral Bone Disorder (CKD-MBD) is a systemic disorder which includes abnormal bone chemistry, vascular or soft tissue calcification, and abnormal bone formation. Many of the parameters of CKD-MBD have been associated with an increased mortality risk in renal patients. There were three main facets to this research project. The first aim of this research was to perform two different studies using the Chronic Renal Insufficiency Standards Implementation Study (CRISIS) data. This prospective epidemiological study is designed to identify factors associated with renal progression and survival in the pre-dialysis CKD population. We have shown that for each 0.323mmol/L (1mg/dL) increase in serum phosphate there was a significant stepwise increased risk of death. (HR1.3 (1.1, 1.5) P=0.01). The association of baseline phenotypic data against vascular stiffness measurements was also investigated. Augmentation index measured at the radial artery was associated with a raised systolic blood pressure but no association with biochemical abnormalities was found.We hypothesised that the phosphate effect on survival was related to the effects within the CKD-MBD spectrum and therefore control of secondary hyperparathyroidism would improve bone and cardiovascular parameters. Therefore for the second part of this research we performed a randomised controlled trial to examine the effects of cinacalcet with standard therapy compared to standard therapy alone on bone and cardiovascular parameters in haemodialysis patients with uncontrolled hyperparathyroidism. The change of biochemical parameters and cardiovascular markers were also further explored in secondary analyses alongside survival data. The primary end point of change in vascular calcification at 52 weeks showed no significant difference between arms. As equivalent control of phosphate and iPTH was achieved in both arms secondary analyses were performed. This showed a significant regression of left ventricular hypertrophy and carotid intima-media thickness associated with phosphate but not iPTH reduction. Patients whose phosphate reduced during the study had a survival advantage when followed for 5 years (HR=10.2 (1.1, 104.5) P=0.049). The third part of this research was to investigate iPTH assay variability. We explored the variation in iPTH assays across the North West and paired this with regional audit data. This study showed that despite there being significant variation among iPTH assays across the region the variation in clinical management was still accounting for some variation in achieving PTH targets.In conclusion, serum phosphate, within the normal laboratory range, is associated with an increased mortality in CKD patients. Haemodialysis patients may have improvement of cardiovascular outcomes with tight control of secondary hyperparathyroidism, by whichever therapeutic means. Intact PTH assays variation may alter our clinical management but variation in practice still affects guideline achievement.