The best replacement for parathyroid is thyroid.

The best alternatives to parathyroid are rated as following:
★★★★★  thyroid
★★★  calcitonin
★★★  thyroid gland
  thyroid nodules

Your alternative for parathyroid is not listed? Suggest!
Speaking about parathyroid, one probably shouldn't forget about normal calcium.

Other search terms related to parathyroid and their ratings are:

★★★★★ normal calcium
★★★ low calcium
high calcium
You have in mind a companion for parathyroid and it is not yet here? Propose!

Google Trends

Scale is based on the average worldwide traffic of parathyroid in all years. Click on graph for more.