HDCN Article Review/Hyperlink

Graham KA, Hoenich NA, Tarbit M, Ward MK, Goodship THJ

Correction of acidosis in hemodialysis patients increases the sensitivity of the parathyroid glands to calcium

J Am Soc Nephrol (May) 8:627-632 1997

To determine if acidosis or calcitriol affected the sensitivity of parathyroid glands to calcium, the authors conducted calcium stimulation/suppression tests in 8 hemodialyis patients.

The study consisted of two 6 week periods separated by a 2 weeks wash-out period. Patients received their usual dialyis with 35 mmol/L bicarbonate dialysate for 4 weeks. They then received a dialysis where the dialysate Ca was decreased to zero and then increased to 2.5 mmol/L (all in one treatment). The patients then received IV 2 ug calcitriol after each of three hemodialysis treatments and the curves were repeated. The other arm was identical to the first except the dialysate bicarbonate was increased to 40 mmol/L throughout.

There were differences in ionized Ca (Ica) or P levels in the 2 groups. The bicarbonate levels were 18.6 at baseline and 25.3 with correction of the bicarbonate level. After correct of the acidosis the majority of the PTH-ICa curves moved down ward and to the left, suggesting increased sensitivity to Ca. There was no effect of calcitriol (data not given). The authors suggest that dialysate bicarbonate should be individualized to maintain pre-dialysis bicarbonate > 22 mmol/L and post-dialysis bicarbonate between 28 and 32 mmol/L to avoid post-dialysis alkalosis.

Comment: If correction of the low bicarbonate increases the sensitivity of the parathyroid glands to Ca, one would expect the baseline PTH values to decrease. Oddly, no values are given. Therefore, one cannot rule out an acute effect of the higher dialysate bicarbonate on PTH secretion as the sole etiology of the results. If acidosis really decreases the sensitivity of the gland to Ca, it would be of interest to know the status of the Ca receptor. The authors are quite right in recommending monitoring the post-dialysis bicarbonate in those patients treated with a high bicarbonate dialysate. (James A. Delmez, M.D., Washington University, St. Louis, MO)