Most calcium stones trace back to diet and urine chemistry. But for a small group of stone formers, the real problem is a pea-sized gland behind the thyroid. Primary hyperparathyroidism — one or more parathyroid glands producing too much parathyroid hormone — pulls calcium out of bone, raises blood calcium, and spills the excess into urine. It is one of the few stone causes that is genuinely curable, and it is frequently missed.
Primary hyperparathyroidism is common enough to matter — roughly 1 in 1,000 people — and more common in women, especially after menopause. The catch is that many patients have no dramatic symptoms; the condition is often found when a routine blood test shows calcium slightly above normal. For a stone former, the clue is the pattern: recurrent calcium stones, especially with high blood calcium or low bone density, should prompt a check of PTH. The 24-hour urine test that every stone former should do becomes the map — high urine calcium with high blood calcium points away from diet and toward the gland.
The treatment is striking in its effectiveness. Parathyroidectomy — removing the abnormal gland — normalizes calcium quickly and, in the Saint John's data, about 90 percent of patients form no new stones afterward. Cambridge University Hospitals NHS notes the surgery is usually short and can be curative, with calcium monitored afterward. Medication and monitoring are reserved for people who cannot have surgery or have only mildly elevated calcium.
While the diagnosis is pending, the low-oxalate plate keeps the dietary side of the ledger quiet:
| Food | Oxalate (mg) | Serving | Rating |
|---|---|---|---|
| Water, still | 0 mg | 1 glass | Safe |
| Chicken breast, roasted | 0 mg | 4 oz | Safe |
| Yogurt, plain whole-milk | 5 mg | 6 oz | Safe |
| Apple, fresh | 2 mg | 1 medium | Safe |
| Banana | 6 mg | 1 medium | Safe |
Fluid and the low-oxalate staples are appropriate for anyone with calcium stones while the cause is being worked out. The important note is that people with hyperparathyroidism should not cut dietary calcium on their own — the bone loss side of the condition argues for adequate calcium, and the specific target is set by the clinician managing the case.
If you have recurrent calcium stones, especially with fatigue, bone pain, or a family history, ask your doctor whether calcium and PTH have been checked — it is two blood tests that can find a curable cause. If your blood calcium has ever run high on a routine panel, mention it at the stone visit rather than dismissing it. And treat a stone recurrence as a signal to look beyond diet: when the pattern repeats, the question is not "what did I eat" but "what is my chemistry doing," and the answer sometimes lives in a gland, not a grocery list.
See how oxalate values are measured and verified on our data methodology page.