Hypoparathyroidism, desired phosphate & low or normal calcium

Patient Scenario: Hypoparathyroidism, desired phosphate & low or normal calcium

 

Assessing the Clinical and Laboratory Parameters

Was there a prior parathyroidectomy? Low or undetectable PTH levels are an expected finding. Current calcium and phosphate levels are appropriately managed.

Are parathyroids intact (or partially resected/reimplanted during prior parathyroid surgery)? PTH secretion is suppressed, usually secondary to use of calcium based binders and/or use of vitamin D analogues; Parathyroid gland remains sensitive to ambient ionized calcium, i.e. is not autonomous

• Discontinue or lower dose  of vitamin D analogue
• Lower dose of calcimimetic.

Approximately 3% of all patients are in this category.

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Dialysis Prescription

Lowering the dialysis calcium concentration ( e.g. from 1.25 to 1.0 mmol/L) in this patient may have the effect of providing a stimulus to PTH formation and release.

 

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Phosphate and Calcium Management

Dietary phosphate control, and adherence to prescribed dose of binder is successful.

Phosphate Binders

Therapeutic avenues include;

• Manipulate dose of calcium-based phosphate binder
• No change or increase in calcium-based binder (if already prescribed vitamin D analogues), depending on serum calcium
• Stop aluminum-based binders if prescribed, and check serum aluminum levels.  Aluminum intoxication includes toxic effects on PTH secretion

 

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PTH Management

Vitamin D Sterols

Active 1-hydroxylated vitamin D sterols (calcitriol, 1-alpha) cause direct suppression of  PTH. Therapeutic avenues are based on lowering the effective dose;

• Consider discontinuation of vitamin D analogue
• Switch from daily to alternate day, (night-time) oral dosing.
• Switch to intravenous dosing on dialysis 3- or 2- times weekly

Calcimimetics

Over suppression of parathyroid glands with a calcimimetic  is possible; hypocalcemia with normal Pi control is consistent with this diagnosis

• Modify calcium-based phosphate binder, and vitamin D dose first.
• Reduce the dose of calcimimetic to maintain serum intact PTH levels between 10-50 pmol/L

Guideline suggestions include;

CSN

7. Vitamin D sterols can be used in the treatment of secondary hyperparathyroidism, but should be discontinued when PTH levels decrease below target levels, or if calcium or phosphate levels increase above target levels.

(Grade C)

KDIGO

4.2.4.f) We suggest that, if the intact PTH levels fall below two times the upper limit of normal for the assay, calcitriol, vitamin D analogs, and/or calcimimetics be reduced or stopped (2C).