Bone density ?
I had my bone density pre-op and again at 18 months. My bone density had actually increased slightly at 18 months. I was much higher than the average person my age on the scale. I take 1260 mg of Calcium Citrate +D daily now. Much of the time since surgery I did the 2400 mg Tums or Viactin daily. Why the change in dosage? My surgeon told me I was just wasting the money that 1000 gms a day was all I needed.
I hope when you see the doctor that it will be something you can quickly correct. Like you, I figure if they want you to come in there is a problem. I've read that people with thyroid problems have more problems with calcium.
Best of luck!