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Article Review/Hyperlink
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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)
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