A 66-year-old woman is evaluated in hospital for serum and laboratory findings. A diagram is shown illustrating her serum parathyroid hormone (PTH) levels versus serum calcium levels. A magenta point represents her results. Which of the following is the most likely explanation for these findings?
Hypoparathyroidism
Lobular carcinoma of the breast
Osteomalacia
Osteoporosis
Primary hyperparathyroidism
