Mysterious PTH values after parathyroidectomy in a patient on maintenance dialysis

A 25-year-old patient with end-stage renal disease on maintenance peritoneal dialysis underwent parathyroidectomy when his secondary hyperparathyroidism did not respond to medical management. However, over the subsequent months he developed extremely raised parathyroid hormone (PTH) levels. When surgical removal of the autotransplant was considered, preoperative work-up revealed a PTH level within the target range. It became apparent that the very high PTH values were due to the location of the blood draw close to the autotransplant, thus measuring a local rather than the systemic PTH value. The multiple causes of varying PTH measurements other than clinical and physiological reasons are reviewed.