Metabolic studies in kidney stone disease.

Patients with kidney stones (n = 59) and healthy controls (n = 31) collected a 24-hour urine sample and later underwent a 6-hour 'fast and load' test in which an oral calcium load was taken after 2 hours. In the 24-hour urine sample, mean calcium excretion was higher in patients than controls, while mean urate, oxalate and citrate levels were similar. The patients had higher levels of fasting plasma calcium, serum calcitriol and fasting urinary calcium, and lower levels of plasma phosphate than did the controls. Following the calcium load, plasma and urinary calcium increased similarly in both groups. Serum parathyroid hormone (PTH) levels were similar in both groups and decreased similarly following the calcium load. Multiple linear regression, relating the presence or absence of stone formation to all variables, found the only variables significantly related to stone formation to be plasma levels of calcium (p less than 0.001) and phosphate (p = 0.001) and fasting urinary urea (p less than 0.001), and 24-hour urinary calcium excretion (p less than 0.05). Urinary oxalate and citrate were not related to stone formation. The data do not support the hypothesis that primary stimulation by calcitriol produces a normal fasting plasma calcium level, with an exaggerated increase after an oral calcium load. The findings instead suggest an abnormality of parathyroid cell 'set point', such that PTH secretion continues until the plasma calcium level is a little higher and the phosphate a little lower than in controls.

Measurement of bone in the os calcis: a clinical evaluation.

Bone mineral content (BMC) was measured in the os calcis of 232 normal subjects aged 17-82 years. The mean reproducibility (coefficient of variation) of the measurement was 1.8%. Substantial bone loss occurred between the ages of 20 and 50 years, and in females the menopause was associated with additional bone loss. There was no significant difference in the rate of bone loss in females and males, but the mean BMC was greater at all ages in males than in females. We also compared os calcis BMC with spinal bone mineral density (BMD), measured by quantitative computed tomographic (CT) scanning, in 85 subjects: 33 were normal controls, 19 had osteoporosis defined by the presence of one or more pathological fractures, and in the remainder the CT examination was performed at the patient's request. Os calcis BMC correlated with spinal BMD in both females (r = 0.69, p less than 0.001) and males (r = 0.84, p less than 0.001). However, the os calcis BMC did not reliably predict spine values around the CT "fracture threshold" of 90-100 mg/cm3 and did not correlate with osteoporotic fracture as well as did spinal BMD. It is concluded that measurement of the os calcis BMC is of limited clinical usefulness for the early diagnosis of osteoporosis.

Bone mass is low in relatives of osteoporotic patients.

STUDY OBJECTIVE: To determine whether the failure to attain normal bone mass in young adulthood contributes to the later development of osteoporotic fractures. DESIGN: Case-control study. SETTING: Referral-based bone clinic at a large teaching hospital. PATIENTS: Sequential sample of 35 asymptomatic relatives, aged 19 to 59 years, of patients with osteoporotic fractures, and 24 patients with osteoporotic fractures. MEASUREMENTS AND MAIN RESULTS: Bone mineral density in the spine was measured by quantitative computed tomographic scanning. Bone mineral content in the os calcis was measured in 19 of the relatives of osteoporotic patients by single-photon absorptiometry. The values for bone mineral density in the spine were corrected to age 50 years with the regression equation derived from the normal values in the controls. The values were lower in relatives of osteoporotic patients than in controls. In men, the mean values (+/- standard deviation [SD]) for relatives were 91 +/- 16 mg/cm3, and for controls, 129 +/- 21 mg/cm3 (P less than 0.001). In women, the mean values for relatives were 96 +/- 17 mg/cm3 and for controls, 126 +/- 19 mg/cm3 (P less than 0.001). In the osteoporotic patients, the corrected mean value for men was 53 +/- 12 mg/cm3, and for women, 77 +/- 20 mg/cm3. The os calcis values did not correlate with the spine values and were mostly well within the normal range. CONCLUSIONS: Mean bone mass is lower in apparently healthy young and middle-aged adult relatives of osteoporotic patients than in normal persons with no family history of osteoporosis. Our findings suggest that the failure to attain an adequate peak bone mass may play an important role in the later development of osteoporotic fractures. Relatives of osteoporotic patients should be advised to have measurements of bone mass taken. This measurement should be taken at the spine, because peripheral sites do not appear to provide adequate information about early osteoporosis.