Parathyroid hormone secretion in chronic renal failure.

The aim of study was to introduce and evaluate a method for quantifying the parathyroid hormone (PTH) secretion during hemodialysis in secondary hyperparathyroidism due to end-stage renal failure. We developed a method suitable for inducing sequential hypocalcemia and hypercalcemia during hemodialysis. During the development of the method we found significantly different results of blood ionized calcium and serum PTH concentration when obtained from the arterial blood line on the dialysis unit or from peripheral venous blood. However, when corrected for the calculated recirculation of 3 to 25%, the result obtained from arterial blood was comparable to the result from venous blood. Furthermore, the results obtained from venous blood were comparable to the results of sequential citrate and calcium clamping performed on a non-dialysis day. From our data of venous blood during hemodialysis, blood PTH/ionized calcium curves were constructed, and a mean calcium set-point of 1.16 mmol/liter was estimated compared to the normal mean of about 1.13 mmol/liter. In conclusion, we demonstrate that it is important to use a standardized method to evaluate parathyroid hormone dynamics in chronic renal failure. By the use of a standardized method we show that the calcium set-point is normal or slightly elevated, indicating normal parathyroid reactivity to calcium in chronic renal failure.