Hyperparathyroidism is reported to be present in 2–8 % of kidney stone formers [6]. Therefore, those seen in a stone clinic or stone referral center have a higher likelihood of having this glandular disorder, and the degree of suspicion for hyperparathyroidism should be relatively high. Serum calcium evaluation is the simplest way to screen for hyperparathyroidism, but it may not be persistently elevated, and defining the upper limit of abnormal has been difficult. A blatantly high serum calcium (>10.5 mg/dL on most total calcium assays) may prompt immediate testing and diagnosis of hyperparathyroidism. Surgical treatment by removal of the gland(s) may then correct the problem. But serum calcium within normal laboratory ranges should not necessarily rule out further work up. Normal calcium in hyperparathyroidism has been described and is not rare in stone formers. The fact that the patient has already formed a stone should heighten suspicion of abnormal parathyroid activity, and normal serum calcium in this case should not end the evaluation for it.

If calcium phosphate is present in at least 5 % of a patient’s stone, the parathyroid axis (blood calcium, phosphorus, parathyroid hormone, and 25-OH vitamin D) should be tested, even if serum calcium was previously normal. To evaluate for phosphorus and calcium wasting, fractional excretion of phosphorus and calcium can be checked when the blood tests are being done. These tests may identify patients with elevated urine phosphorus, low serum phosphorus, and relatively normal PTH levels, which would suggest a primary leak of phosphorus at the level of the kidney. A check of 1,25 vitamin D is not needed in the majority of patients. However, if sarcoidosis or malignancy is suspected, this test should be done. Hypophosphatemia may suggest disorders of renal phosphate reabsorption such as mutations in the genes encoding the sodium-phosphate cotransporters.