Effect of testosterone treatment on bone mineral density in men over 65 years of age

As men age, their serum testosterone concentrations decrease, as do their bone densities. Because bone density is also low in hypogonadal men, we hypothesized that increasing the serum testosterone concentrations of men over 65 yr to those found in young men would increase their bone densities. We randomized 108 men over 65 yr of age to wear either a testosterone patch or a placebo patch double blindly for 36 months. We measured bone mineral density by dual energy x-ray absorptiometry before and during treatment. Ninety-six men completed the entire 36-month protocol. The mean serum testosterone concentration in the men treated with testosterone increased from 367 +/- 79 ng/dL (+/-SD; 12.7 +/- 2.7 nmol/L) before treatment to 625 +/- 249 ng/dL (21.7 +/- 8.6 nmol/L; P < 0.001) at 6 months of treatment and remained at that level for the duration of the study. The mean bone mineral density of the lumbar spine increased (P < 0.001) in both the placebo-treated (2.5 +/- 0.6%) and testosterone-treated (4.2 +/- 0.8%) groups, but the mean changes did not differ between the groups. Linear regression analysis, however, demonstrated that the lower the pretreatment serum testosterone concentration, the greater the effect of testosterone treatment on lumbar spine bone density from 0-36 months (P = 0.02). This analysis showed a minimal effect (0.9 +/- 1.0%) of testosterone treatment on bone mineral density for a pretreatment serum testosterone concentration of 400 ng/dL (13.9 nmol/L), but an increase of 5.9 +/- 2.2% for a pretreatment testosterone concentration of 200 ng/dL (6.9 nmol/L). Increasing the serum testosterone concentrations of normal men over 65 yr of age to the midnormal range for young men did not increase lumbar spine bone density overall, but did increase it in those men with low pretreatment serum testosterone concentrations.

Osteoporosis and bone morbidity in cardiac transplant recipients

PURPOSE

To evaluate the incidence and etiology of osteopenia and pathologic fractures in cardiac transplant recipients.

PATIENTS

Thirty-one adult male cardiac transplant recipients and 14 adult men with congestive heart failure (CHF) awaiting cardiac transplantation.

METHODS

Assessment of indices of bone and mineral metabolism and of bone mineral density (BMD) by dual-energy x-ray absorptiometry.

RESULTS

BMD in the proximal femur was below normal in both groups compared to that in age-matched control subjects, whereas BMD in the lumbar spine was normal. There was no significant difference in BMD at any site between the two groups. No clinical parameter predicted BMD. In all patients, laboratory indices of bone mineral metabolism, except parathyroid hormone (PTH) levels, were normal and not statistically different between the two groups. CHF patients had a trend toward elevations of PTH, 1,25-dihydroxyvitamin D, and urinary calcium excretion compared to transplant patients. Eight of 31 transplant patients and 2 of 14 CHF patients had vertebral compression fractures (c2 = 11.8, p < 0.0006). Transplant recipients with fractures had twice as many rejection episodes as did transplant patients without fractures, but did not differ in cumulative dose of steroids. Two patients developed avascular necrosis of the femoral head following transplantation.

CONCLUSIONS

Cardiac transplant recipients and patients with CHF awaiting transplantation had decreased hip BMD, but normal spine BMD. Although immunosuppressive therapy did not appear to influence bone mass, loop diuretics prior to transplantation may have stimulated a mild secondary increase in PTH that could have differentially caused loss of bone density at the hip in both groups. Pulse corticosteroids used in treating rejection may have contributed to the increased incidence of vertebral fractures in transplant patients. These data suggest that severe CHF with its associated diuretic use and decreased activity are primary contributors to osteopenia in these patients.

A longitudinal study of metacarpal bone morphometry in anorexia nervosa

Osteoporosis is a known complication of anorexia nervosa. Although calorie and mineral malnutrition may contribute to changes in bone mass and morphometry, hypoestrogenism is thought to be the most important etiologic factor. In a seven-year longitudinal study of six women aged 19 to 35 years with adolescent-onset anorexia nervosa, the objective was to correlate menstruation and bone morphometry. At the onset of the study, five women were amenorrheic and had abnormal metacarpal bone morphometry. After seven years, three women remained amenorrheic and below 85% of ideal body weight. Anteroposterior roentgenographs of the nondominant second metacarpal taken at the beginning and end of the study revealed an increase in medullary canal diameter (p less than 0.03) and medullary area (p less than 0.04) and a decrease in combined cortical thickness (p less than 0.04) and percent cortical area (p less than 0.02). These findings suggest progressive endosteal resorption in the absence of compensatory periosteal apposition. Such bone remodeling characteristics are distinctly abnormal in this age group. The three women who regained menses showed up to one third less endosteal resorption and less cortical thinning than did the three women who remained amenorrheic. Resumption of menses may be an important milestone in preventing further cortical bone loss in anorexia nervosa.

Management of severe hypercalcemia

Severe hypercalcemia is a medical emergency requiring urgent treatment. It most commonly is caused by malignant tumors, as in the case study, but can also be caused by advanced hyperparathyroidism or high serum levels of vitamin D. The patient described in the case study shows clinical evidence of volume contraction due to hypercalcemia-related anorexia and vomiting. His elevated serum concentrations of urea nitrogen and creatinine reflect intravascular volume depletion and hypercalcemia-induced reduction of renal perfusion. He is also likely to have irreversible renal damage as a result of nephrocalcinosis. His central nervous system depression is most likely a result of hypercalcemia, but other central nervous system disorders such as cerebral metastases should be considered. Appropriate treatment would include intravenous fluids to correct volume depletion, dilute extracellular fluid calcium, and promote renal calcium excretion. Before waiting for the effects of volume expansion, the first dose of an inhibitor of bone resorption should be given. The agent of choice now (this may change when second-generation bisphosphonates become available) is plicamycin. Etidronate is a reasonable second choice. Because both drugs require at least 48 hours before their hypocalcemic action is manifest, calcitonin could be used to accelerate the rate of decline of the serum calcium. As the patient becomes more alert, weight-bearing and ambulation should be encouraged. With this combination of therapeutic modalities, this patient's serum calcium level should be corrected within 3 to 5 days. Intermittent injections of mithramycin or etidronate could be given on an outpatient basis approximately once a week in order to maintain the serum calcium within the normal range. One of the most important aspects of treatment in hypercalcemic patients is eradication of the underlying disease, which usually calls for specific antitumor therapy, including chemotherapy, radiation therapy, or surgery. Most of the agents currently available for the correction of hypercalcemia have cumulative toxicities or are only transiently effective and, therefore, their use should be considered a temporizing measure until specific treatment directed at the primary disease takes effect.

WR-2721 reduces bone loss after hindlimb tenotomy in rats

WR-2721 is a thiophosphate analog of cysteamine that produces hypocalcemia in vivo. Previous studies suggest that WR-2721 produces hypocalcemia by independent inhibitory effects on parathyroid hormone (PTH) secretion, osteoclastic bone resorption, and tubular reabsorption of calcium. We sought to determine if WR-2721 would decrease bone loss in an animal model of disuse osteoporosis produced by unilateral knee tenotomy in the rat. Tenotomy significantly increased osteoclast number in tibias on the side of the procedure compared with tibias on the opposite side which had not undergone the procedure at 3 and 14 days. Femoral weight of tenotomized limbs were also reduced significantly compared with the contralateral limb at 3 and 14 days. WR-2721 treatment (240 mg/kg daily) prevented 26% of the loss of femoral dry weight and 29% of the loss of femoral ashed weight produced 14 days after tenotomy. In addition, WR-2721 treated (240 mg/kg daily) animals had fewer osteoclasts in tenotomized tibias than control animals at 3 days (6.6 +/- 0.7/mm versus 10.3 +/- 0.9/mm, p less than 0.02) and at 14 days (5.8 +/- 0.3/mm versus 8.7 +/- 0.4/mm, p less than 0.02). These data suggest that WR-2721 decreases bone loss in this model by decreasing osteoclastic bone resorption.

Treatment of hypercalcemia

Severe hypercalcemia is a potentially life-threatening complication of several diseases. Most commonly it is caused by cancers that enhance bone resorption. Impaired renal calcium excretion resulting from a combination of volume contraction and calcium-induced renal injury (nephrocalcinosis) plays a critical role in the genesis and aggravation of hypercalcemia. Treatment of hypercalcemia is based on treating the underlying disease, restoring extracellular volume, correcting electrolyte deficiencies (potassium and magnesium), and reducing bone resorption. Several measures are available to reduce bone resorption, of which the most efficacious are the bisphosphonates and plicamycin (mithramycin). One of these agents in combination with volume expansion can reduce serum calcium concentrations to near normal in most patients within 3 to 6 days. Because of the delayed hypocalcemic action of these agents, they should be administered early. Calcitonin has a more modest hypocalcemic action than the bisphosphonates or plicamycin but has a more rapid effect. Combining calcitonin with plicamycin or a bisphosphonate can enhance the rate of decline of the serum calcium level. Bone resorption also can be reduced by getting patients out of bed to stand or walk. Glucocorticoids may be effective in patients with hypercalcemia associated with high levels of vitamin D, such as sarcoidosis, some lymphomas, or vitamin D intoxication. Patients with mild to moderate hypercalcemia may be asymptomatic. Therapy in these patients should be directed at the primary disease as well as at preventing complications that could raise the level of serum calcium. Efforts should be made to prevent volume contraction and prolonged bed rest. Sedatives and narcotic analgesics, by reducing activity and oral intake, can raise serum calcium levels. In the future it may be possible to predict which patients with cancer are likely to develop accelerated local tumor-mediated or humorally mediated osteolysis. For example, high circulating levels of PTH-like peptides in patients with lung cancer might suggest a greater risk of developing hypercalcemia. These patients could be monitored more closely by periodically measuring urinary calcium. Another prophylactic approach would be to treat patients at risk of developing hypercalcemia with drugs, such as the bisphosphonates, that inhibit bone resorption.

Primary hyperparathyroidism in infancy

Primary hyperparathyroidism in the neonate is a rare and often fatal disorder. These infants typically display severe hypercalcemia, respiratory distress, muscular hypotonia, and skeletal demineralization. They are usually diagnosed within the first three months of life and have hyperplasia of the four parathyroid glands. Twenty-nine infants with primary hyperparathyroidism are reported in the literature. Mortality is 87.5% in medically managed patients and 24% in surgically managed patients. Surgical management has not been satisfactory, in that recurrent hypercalcemia has been encountered in most patients undergoing subtotal parathyroidectomy, and total parathyroidectomy has resulted in the need for lifelong calcium and vitamin D supplementation. We have recently cared for a term newborn female in whom the diagnosis of primary hyperparathyroidism was made clinically on the second day of life, and later was confirmed biochemically. The baby underwent neck exploration on the 11th day of life and was successfully treated with total parathyroidectomy and parathyroid autotransplantation. Although initially rendered eucalcemic, the infant subsequently developed recurrent hypercalcemia requiring the removal of some of the autograft. Currently, the child is more than 2 years following surgery, growing well, and off all medication. The world literature is reviewed in this report of one of the first and the youngest infants, to our knowledge, to undergo parathyroid autotransplantation. In view of its success in avoiding the complication of repeated neck exploration for recurrent hyperparathyroidism or the creation of permanent hypoparathyroidism, we recommend this surgical approach for the rare neonate with primary hyperparathyroidism.

Modulation of intracellular Ca2+ in the parathyroid cell. Release of Ca2+ from non-mitochondrial pools by inositol trisphosphate

Stimuli which enhance secretion from parathyroid cells such as low extracellular Ca2+ or Mg2+ are associated with a decrease in the cytosolic Ca2+ concentration as measured by quin2. Current evidence suggests that increased production of inositol 1,4,5-triphosphate (IP3) releases Ca2+ from cellular stores thus increasing cytosolic Ca2+. We used saponin-permeabilized dispersed bovine parathyroid cells to study the effect of IP3 on intracellular Ca2+. IP3 released Ca2+ from these cells in a dose-dependent manner; half-maximal response occurred with 0.3 microM IP3 and maximal response with 1.2 microM IP3. Permeabilized cells incubated in the presence of the mitochondrial inhibitor antimycin A released a similar amount of Ca2+ suggesting that IP3 releases Ca2+ from a non-mitochondrial pool. These results suggest that IP3 regulates cytosolic Ca2+ in this system and may function as a second messenger controlling hormone secretion.

Bone and parathyroid inhibitory effects of S-2(3-aminopropylamino)ethylphosphorothioic acid. Studies in experimental animals and cultured bone cells

S-2-(3-aminopropylamino)ethylphosphorothioic acid (WR 2721) is a radio- and chemoprotective agent which produces hypocalcemia in humans. Intravenous injection of 30 mg/kg WR 2721 in rats and 15 mg/kg in dogs lowers serum calcium by 19 and 25%, respectively. Hypocalcemia in dogs is associated with a fall in serum immunoreactive parathyroid hormone (PTH), which suggests that the mechanism of its hypocalcemic effect is acute hypoparathyroidism. Despite this effect on PTH, in eight chronically parathyroidectomized rats on a low phosphate diet, WR 2721 reduced serum calcium from 9.4 +/- 0.6 to 7.7 +/- 0.5 mg/dl (P less than 0.01) at 3 h. Furthermore, in dogs rendered hypercalcemic by continuous infusion of PTH, WR 2721 reduced serum calcium from 11.0 +/- 0.5 to 10.6 +/- 0.5 mg/dl (P less than 0.01). To determine whether WR 2721 causes hypocalcemia by enhancing the exit of calcium from the circulation or inhibiting its entry, the drug was infused 3 h after administration of 45Ca to rats. WR 2721 did not significantly increase the rate of disappearance of 45Ca from the circulation even though serum calcium fell by 19%. However, serum 45Ca specific activity was higher at 1.5 h (P less than 0.01) and 3 h (P less than 0.05) in rats given WR 2721 than in rats given vehicle alone, which suggests that WR 2721 blocks the entry of nonradioactive calcium into the circulation, presumably from bone. In incubations with fetal rat long bone labeled in utero with 45Ca, 10(-3) M WR 2721 inhibited PTH-stimulated, but not base-line release of 45Ca. Bone resorption by primary culture of chick osteoclasts was inhibited by WR 2721 at concentrations as low as 10(-4) M in the absence of hormonal stimulation. These studies suggest that WR 2721 lowers serum calcium predominantly by blocking calcium release from bone. This acute hypocalcemic effect is at least in part independent of its effect on the parathyroid glands, and is most likely a direct effect of the agent on bone resorption.

Urinary calcium excretion in familial hypocalciuric hypercalcemia. Persistence of relative hypocalciuria after induction of hypoparathyroidism

Familial hypocalciuric hypercalcemia (FHH) is an autosomal dominant trait comprising hypercalcemia, hypophosphatemia, parathyroid hyperplasia, and unusually low renal clearance of calcium. We evaluated the role of parathyroid hormone in the relative hypocalciuria of FHH and characterized the renal transport of calcium in this disorder using three previously hypercalcemic FHH patients with surgical hypoparathyroidism and three controls with surgical hypoparathyroidism. Intravenous infusion of calcium chloride in two patients with FHH and in three controls increased serum calcium from a mean basal of 5.0 to a mean peak of 6.8 meq/liter in two FHH patients and from 4.2 to 5.7 in three control subjects. Urinary calcium in a third FHH patient was studied without calcium infusion during recovery from hypercalcemia of vitamin D intoxication. At all serum concentrations of calcium, calcium clearance was lower in FHH than in controls; at base-line serum calcium, the ratio of calcium clearance to inulin clearance (C(Ca)/C(IN)) in FHH subjects was 32% of that in controls and decreased to 19% during hypercalcemia. Calcium infusion increased the ratio of sodium clearance to inulin clearance in controls from a base line of 0.020 to 0.053 at peak concentrations of calcium in serum, but did not affect this parameter in FHH (0.017 at base-line serum calcium vs. 0.019 at peak). When calcium infusion studies were performed (in two patients with FHH and one control) during administration of acetazolamide, a drug whose principal renal action causes inhibition of proximal transport of solute, C(Ca)/C(IN) in the patients with FHH was 29 and 7% of that of the control at base-line and peak serum calcium, respectively. In contrast, ethacrynic acid, a diuretic that acts in the ascending limb of the loop of Henle, increased C(Ca)/C(IN) more in the FHH patients than in the control subject; C(Ca)/C(IN) was 65% at base-line and 47% at peak serum calcium, compared with that of the control subject. The greater calciuric response to ethacrynic acid than to acetazolamide or calcium infusion alone in FHH indicates that a major renal locus of abnormal calcium transport in this disorder may be the ascending limb of the loop of Henle.Decreased clearance of calcium in patients with FHH and hypoparathyroidism when compared with hypoparathyroid controls indicates that relative hypocalciuria in FHH is not dependent on hyperparathyroidism. Since the parathyroid glands in FHH are not appropriately suppressed by calcium, this implies that FHH represents a disorder of abnormal transport of, and/or response to, extracellular calcium in at least two organs, parathyroid gland and kidney.

An association between neonatal severe primary hyperparathyroidism and familial hypocalciuric hypercalcemia in three kindreds

Four cases of neonatal severe primary hyperparathyroidism occurred in three families; familial hypocalciuric hypercalcemia was present in each kindred. The diagnosis of familial hypocalciuric hypercalcemia was based on the following features; hypercalcemia in many relatives (eight to 16 per kindred), without other features of the multiple endocrine neoplasia syndromes; recognition of hypercalcemia before the age of 10 in one to three relatives; hypocalciuric hypercalcemia in all relatives tested (five to 14 per kindred); and abnormal serum calcium levels despite parathyroidectomy in all additional relatives (one to five per kindred) undergoing this operation. The association of two uncommon syndromes (neonatal severe primary hyperparathyroidism and familial hypocalciuric hypercalcemia) in these kindreds suggests that the two syndromes share a common genetic cause within each kindred.

Parathyroid imaging after intraarterial injections of [75Se]selenomethionine

Thirteen patients with persistent hyperparathyroidism after unsuccessful neck surgery were given up to 250 microCi [75Se]selenomethionine intraarterially during parathyroid arteriography, gamma-Camera images of the neck and mediastinum localized abnormal parathyroids in four of five patients receiving complete injections, despite very small glands or unsuccessful arteriograms in some of the patients. Correctly localizing images were obtained in three patients receiving incomplete injections. However, images in five of eight of the remaining patients receiving incomplete injections showed areas of false positive uptake, and there was no way preoperatively to distinguish these from the true positive studies. We conclude that intraarterial injection of radioselenomethionine is a simple supplementary procedure in patients undergoing arteriography that may, with proper technique, be useful in identifying small foci of abnormal parathyroid tissue.

Maximal urine-concentrating ability: familial hypocalciuric hypercalcemia versus typical primary hyperparathyroidism

Impairment of urine-concentrating ability is common in persons with chronic hypercalcemia. We assessed urine-concentrating ability in 40 patients with typical primary hyperparathyroidism and 10 patients with familial hypocalciuric hypercalcemia, a disorder resembling typical primary hyperparathyroidism but lacking some of its clinical complications. Urine-concentrating ability was determined during a dehydration test of 18-22 h. The two patient groups were comparable with respect to serum calcium concentration and creatinine clearance. In the group with familial hypocalciuric hypercalcemia, the duration of hypercalcemia was probably greater, because it commences during infancy; the urinary excretion rate for calcium was lower [6.6 +/- 5.4 (mean +/- 1 SD) vs. 14.8 +/- 7.5 meq/day; P less than 0.005]. Patients with familial hypocalciuric hypercalcemia showed higher maximal urinary osmolality (800 +/- 150 vs. 664 +/- 130 mosmol/kg; P less than 0.0005). Among the patients with typical primary hyperparathyroidism, there was a negative association between maximal urinary osmolality and urinary cAMP (r = -0.40; P less than 0.05), but there was no significant relation between maximal urinary osmolality and the urinary excretion rate for calcium. Among 18 patients retested within 1 month after surgical correction of typical primary hyperparathyroidism, urine-concentrating ability did not improve. In patients with typical primary hyperparathyroidism, impairment in urine-concentrating ability reflects features of the chronic disease state, as it is not rapidly reversible by correction of that state. However, in patients with familial hypocalciuric hypercalcemia, longstanding hypercalcemia is not associated with obvious impairment of urine-concentrating ability. Complete or partial freedom from impairment of urine-concentrating ability and from calcareous renal disease are expressions of the generally mild course in familial hypocalciuric hypercalcemia.

Characterization of the dopamine-responsive adenylate cyclase of bovine parathyroid cells and its relationship to parathyroid hormone secretion

To investigate further the mechanism of dopamine (DA)-stimulated and parathyroid hormone (PTH) secretion, we have identified and studied DA-sensitive adenylate cyclase in a particulate preparation of osmotically lysed dispersed bovine parathyroid cells. Adenylate cyclase was responsive to DA at concentrations as low as 0.3 microM, and the maximal stimulation in the presence of GTP was 2- to 4-fold that of activity with GTP alone. (-)Propranolol (1 microM) abolished the stimulation by (-)isoproterenol but did not inhibit the DA-stimulated adenylate cyclase, whereas alpha-flupenthixol (1 microM) inhibited DA stimulation but not that of (-)isoproterenol. The dopaminergic agonists epinine and 6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene were nearly as effective as DA in stimulating the enzyme, while apomorphine displayed partial agonist activity. The dopaminergic antagonists chlorpromazine, fluphenazine, and haloperidol inhibited the DA-stimulated adenylate cyclase. There was a close correspondence between the Ka values for DA and the Ki values of the dopaminergic antagonists for particulate adenylate cyclase activity, cellular cAMP accumulation, and PTH release. These results indicate that DA-stimulated cAMP accumulation and PTH release are mediated through specific activation of a DA receptor linked to adenylate cyclase.

Prostaglandin-mediated stimulation of adenosine 3',5'-monophosphate accumulation and parathyroid hormone release in dispersed human parathyroid cells

Freshly dispersed cells were employed to study the effects of various prostaglandins (PGs) on cAMP accumulation and parathyroid hormone release in abnormal human parathyroid tissue. PGE1 and PGE2 effected dramatic increases in intracellular cAMP accumulation over a concentration range of 10(-6)-10(-4) M; the relative effectiveness of these agents varied among different preparations. PGF2 alpha caused a smaller stimulation of cAMP accumulation, and PGF1 alpha was generally without effect. In contrast with the effect previously described in the bovine parathyroid cell system, PGF2 alpha did not suppress agonist-stimulated cAMP accumulation. Both PGE1 and PGE2 enhanced cellular release of parathyroid hormone, with dose-response characteristics similar to those seen with cAMP. In addition, both agents led to a significant stimulation of adenylate cyclase activity in a cellular homogenate preparation. Neither indomethacin (10(-5) M) nor naproxen (10(-4) M) altered the calcium suppressibility of the cells, suggesting that endogenous PG production does not play a major role in the calcium-mediated regulation of parathyroid hormone release.

Adenosine 3',5'-monophosphate response to parathyroid hormone: familial hypocalciuric hypercalcemia versus typical primary hyperparathyroidism

We investigated cAMP metabolism during and after a 15-min infusion of parathyroid hormone (PTH) in 7 normals, 13 patients with typical primary hyperparathyroidism (1HPT), and 6 patients with familial hypocalciuric hypercalcemia (FHH). Nephrogenous urinary cAMP excretion rate reached a peak during the first or second 30 min urine collection interval after the start of the PTH infusion in all subjects. cAMP concentration in plasma reached a peak within 5--20 min of the start of the infusion and then decreased with an initial half-time of 15 min. The peak value of nephrogenous urinary cAMP excretion rate was lower in the group with 1HPT than in the group with FHH or in normals (119 vs, 275 vs. 204 nmol/100 ml glomerular filtrate; P less than 0.0 5 for both comparisons). Similarly, the peak value of plasma cAMP concentration was less in 1HPT subjects than in FHH patients or in normals (11.1 vs. 17.1 vs. 16.6 nmol/100 ml, respectively; P less than 0.05 for both comparisons). For purposes of diagnostic classification, the two hypercalcemia groups could be more completely separated by the values of either the renal calcium to creatinine clearance ratio or the plasma PTH concentration than by the values of inidices of cAMP response to PTH. The differences in cAMP response to PTH between FHH and 1HPT patients could be secondary to differences in circulating PTH concentrations (these are lower in subjects with FHH) or could reflect a renal lesion more closely related to the underlying etiology of FHH.

Familial hypocalciuric hypercalcemia: recognition among patients referred after unsuccessful parathyroid exploration

Of 67 patients referred after unsuccessful surgery for presumed primary hyperparathyroidism, six were shown to be members of kindreds with familial hypocalciuric hypercalcemia. This diagnosis had not been recognized in any of the six previosuly. Most of the remaining 61 cases had proven or probable typical primary hyperparathyroidism, and a subgroup of four had hypercalcemia with suppression of the parathyroid glands. Urine calcium excretion expressed as the calcium:creatinine clearance ratio provided an easily measurable and effective index to separate the groups with familial hypocalciuric hypercalcemia, typical primary hyperparathyroidism, and suppressed parathyroids. Thus, at least 9% of patients referred after unsuccessful parathyroidectomy had familial hypocalciuric hypercalcemia. The assessment of urine calcium excretion by indices such as the calcium:creatinine clearance ratio should facilitate recognition of this condition, which responds poorly to standard subtotal parathyroidectomy.