Potential Clinical Utility of a New IRMA for Parathyroid Hormone in Postmenopausal Patients with Primary Hyperparathyroidism

Full-length versus intact PTH concentrations in pseudohypoparathyroidism type 1 and primary hyperparathyroidism: clinical evaluation of immunoassays in individuals from China

PURPOSE

The application of the third-generation parathyroid hormone (PTH) assay [PTH(1-84) assay] for evaluating PTH levels in patients with pseudohypoparathyroidism type-1 (PHP1) is less popular than the second-generation assay. Therefore, we aimed at examining the conformity between the PTH(1-84) assay and the intact PTH (iPTH) assay, specifically examining their performance in individuals with PHP1 versus individuals with primary hyperparathyroidism (PHPT), compared to healthy controls.

METHODS

PTH(1-84) and iPTH assay were performed in patients with PHP1, patients with PHPT, and healthy volunteers. ∆PTH%, PTH(1-84)/iPTH (3^rd/2^nd ratio), iPTH/upper limit of normal (ULN), and PTH (1-84)/ULN of each group were calculated for comparison. Linear regression, Kappa conformity test, and Bland-Altman analysis of ∆PTH/mean of iPTH and PTH(1-84) (percent bias) plotted against the mean of iPTH and PTH(1-84) were performed to determine the conformance of PTH(1-84) assay with iPTH assay.

RESULTS

A total of 54 patients with PHP1, 127 patients with PHPT, and 65 healthy volunteers were enrolled in this study. All the three groups showed strong linear relationship between iPTH and PTH (1-84) (r² = 0.9661, 0.7733, and 0.9575, respectively). No significant differences were noted in 3^rd/2^nd ratio (median 0.76 vs. 0.72) between the PHP1 and PHPT groups (p > 0.05). Conformity examination showed the Kappa value was 0.778 and 0.395 for PHP1 and PHPT groups respectively. No difference in the Kappa values was found between PHP1A and PHP1B subgroups. Bland-Altman plot demonstrated that the proportion of data points that were plotted within mean ± 1.96 SD in PHP1, PHPT and normal control groups were 96.3%, 93.7%, and 98.5%, respectively. The mean percent bias of the three groups were 26.1%, 31.2%, and 17.0%, respectively. The range of mean ± 1.96 SD of percent bias of the three groups were 2.2%-50.0%, -14.3%-76.6%, and 6.7%-27.2%, respectively.

CONCLUSION

Although iPTH and PTH(1-84) values were both lower in the present PHP1 cohort than in the PHPT cohort, there appear to be differences in the relative agreement between both immunoassays, and in the relationship between the two values, especially in comparison to healthy controls. Whether these differences are due to differential accumulation of C-terminal fragments or other factors requires further study.

Normocalcaemic primary hyperparathyroidism: An update on diagnostic and management challenges

Normocalcaemic primary hyperparathyroidism is a condition that can present with intermittent hypercalcemia or may evolve into hypercalcemic primary hyperparathyroidism. This milder biochemical entity remains incompletely understood because of a lack of long-term health outcomes regarding both medical and surgical approaches to its management. Medical therapies have shown some efficacy. A limited number of studies have found that bisphosphonates increase bone mineral density, and calcimimetics may decrease the risk of nephrolithiasis in patients with normocalcaemic primary hyperparathyroidism. Studies have also described patient outcomes after applying the same surgical criteria used for patients with hypercalcaemic primary hyperparathyroidism to those with the normocalcaemic form of the disease. These studies suggest that parathyroid surgery appears to be effective in normalizing elevated serum parathyroid hormone concentrations and decreasing adverse renal and skeletal outcomes in patients with normocalcaemic hyperparathyroidism. Given the available data and overall lack of consensus regarding the optimal management of these patients, a reasonable approach is to tailor treatment to the individual patient by considering their risk factors for new or accelerated bone loss, kidney stones, diminished quality of life, and cardiovascular disease.

Clinical Guidelines and PTH Measurement: Does Assay Generation Matter?

PTH is an important regulator of calcium and phosphate homeostasis and bone remodeling. It is metabolized into PTH fragments, which are measured to a different extent by PTH assays of different generations because of differences in fragments recognized and lack of assay standardization. PTH is measured in the workup of several conditions, and clinical guidelines provide recommendations concerning these measurements. This review provides an overview of the impact of differences between PTH assays, applying distinct clinical guidelines for primary and secondary hyperparathyroidism and perioperative use of PTH measurements. Guidelines deal with PTH measurement in different ways, recommending either trend monitoring, the use of a fold increase of the upper reference limit, or an absolute PTH cutoff value. For classic primary hyperparathyroidism (PHPT), the type of PTH assay used will not affect diagnosis or management because the precise concentration of PTH is less relevant. In chronic kidney disease, the guideline recommends treating secondary hyperparathyroidism above a twofold to ninefold PTH increase, which will result in different clinical decisions depending on the assay used. For patients after bariatric surgery, guidelines state absolute cutoff values for PTH, but the impact of different generation assays is unknown because direct comparison of PTH assays has never been performed. During parathyroid surgery, PTH measurements with a third-generation assay reflect treatment success more rapidly than second-generation assays. Increased awareness among clinicians regarding the complexity of PTH measurements is warranted because it can affect clinical decisions.

Calcium and Bone Metabolism Indices

Calcium and inorganic phosphate are of critical importance for many body functions, thus the regulations of their plasma concentrations are tightly controlled by the concerted actions of reabsorption/excretion in the kidney, absorption in the intestines, and exchange from bone, the major reservoir for calcium and phosphate in the body. Parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D (1,25(OH)₂D) control calcium homeostasis, whereas PTH, 1,25(OH)₂D, and bone-derived fibroblast growth factor 23 (FGF 23) control phosphate homeostasis. Hypoparathyroidism can cause hypocalcemia and hyperphosphatemia, whereas deficient vitamin D actions can cause osteomalacia in adults and rickets in children. Hyperparathyroidism, alternatively, can cause hypercalcemia and hypophosphatemia. Laboratory tests of calcium, phosphate, PTH, and 25-hydroxyvitamin D are very useful in the diagnosis of abnormalities associated with calcium and/or phosphate metabolisms. Bone is constantly remodeled throughout life in response to mechanical stress and a need for calcium in extracellular fluids. Metabolic bone diseases such as osteoporosis, osteomalacia in adults or rickets in children, and renal osteodystrophy develop when bone resorption exceeds bone formation. Bone turnover markers (BTM) such as serum N-terminal propeptide of type I procollagen (P1NP) and C-terminal collagen cross-link (CTX) may be useful in predicting future fracture risk or monitoring the response to anti-resorptive therapy. There is a need to standardize sample collection protocols because certain BTMs exhibit large circadian variations and tend to be influenced by food intakes. In the United States, a project to standardize BTM sample collection protocols and to establish the reference intervals for serum P1NP and serum CTX is ongoing. We anticipate the outcome of this project to shine lights on the standardization of BTM assays, sample collection protocols, reference intervals in relation to age, sex, and ethnic origins, and clinical utilities of BTMs. This review will briefly discuss the regulations of calcium and phosphate homeostasis, laboratory's role in the diagnosis, and monitoring of bone and calcium metabolism, as well as the usefulness and controversies of the utilities of BTMs in the diagnosis and monitoring of metabolic bone diseases.

Experience with a third-generation parathyroid hormone assay (BIO-PTH) in the diagnosis of primary hyperparathyroidism in a Brazilian population

OBJECTIVE

To evaluate the usefulness of a third-generation PTH assay in the diagnosis of primary hyperparathyroidism (PHPT).

SUBJECTS AND METHODS

Forty-one PHPT patients (4 men and 37 women) with 61.2 ± 10.9 (mean ± SD) years, were studied and had PTH levels measured with two different methods using the same immunochemiluminescent assay plataform (Elecsys 2010 System, Roche). We compared a second-generation assay (I-PTH) with a third-generation PTH assay (Bio-PTH). Two populations of 423 and 120 healthy adults with serum 25OHD levels above 25 ng/mL were used to define normal values in the I-PTH and Bio-PTH assays respectively.

RESULTS

Normal PTH values based in the healthy adults population were 24.2-78.0 pg/mL for the I-PTH assay and 19.9-58.5 pg/mL for Bio-PTH assay. In PHPT patients, PTH values ranged from 67 to 553 pg/mL (median: 168 pg/mL) using the I-PTH assay and from 55 to 328 pg/mL (median: 111 pg/mL) using the Bio-PTH assay. Results obtained with the Bio-PTH assay were significantly lower (p < 0.0001, Wilcoxon). In general I-PTH and Bio-PTH showed highly significant correlation (r = 0.952, p < 0.0001). Passing-Bablok analysis gave a regression equation of Bio PTH = 13.44 + 0.59 x intact PTH. PHPT patients had 25OHD levels ranging from 4 to 36 ng/mL (mean 16.2 ng/mL); 35 subjects (85.3%) had values bellow 25 ng/mL.

CONCLUSION

Our results demonstrate that both second and third generation PTH methods are strongly correlated in PHPT patients and control subjects. Lower results with Bio-PTH tests are expected in function of the assay specificity determined by the amino-terminal antibody used.

High prevalence of abdominal aortic calcification in patients with primary hyperparathyroidism as evaluated by Kauppila score

OBJECTIVE

The prevalence of abdominal aortic calcification (AAC) in primary hyperparathyroidism (PHPT) is unknown. We assessed both prevalence and severity of AAC in PHPT postmenopausal women.

METHODS

In this study 70 PHPT postmenopausal women and 70 age- and sex-matched controls were enrolled. Each participant underwent biochemical evaluation, lateral spine radiograph, bone mineral density (BMD) measurement (lumbar, femoral, radial sites), and kidney ultrasound. Lateral lumbar films were analyzed in the region of L1-L4 vertebrae and the Kauppila score (a semi-quantitative grading system) was used to assess the severity of AAC.

RESULTS

There were no differences regarding demographic and cardiovascular risk factors in the two groups. PHPT patients had higher prevalence of kidney stones (30% vs 7%, P=0.0008) and lower radial BMD values (0.558±0.071 vs 0.588±0.082 g/cm(2), P<0.05) compared with controls. PHPT patients showed higher prevalence of AAC (31 vs 18, P=0.03), with more severe calcifications (Kauppila score 7.35±6.1 vs 5.05±3.5, P=0.007). PHPT patients with AAC were older and had been suffering from the disease for a longer period compared with those without ACC. Moreover, PHPT patients with severe AAC had mean higher serum parathyroid hormone levels compared with patients with moderate or mild calcifications. In PHPT patients with AAC, multiple regression analysis, adjusted for age and years since diagnosis, showed that only parathyroid hormone significantly correlated with Kauppila score.

CONCLUSION

We found a higher prevalence and severity of AAC in PHPT related to parathyroid hormone effect.

Prevalence of kidney stones and vertebral fractures in primary hyperparathyroidism using imaging technology

CONTEXT

The fourth International Workshop on the Management of Asymptomatic Primary Hyperparathyroidism (PHPT) has recently suggested that skeletal and renal imaging be routinely conducted. So far, no study has systematically assessed this issue.

OBJECTIVE

The objective was to evaluate the prevalence of kidney stones (KS) and vertebral fractures (VFs) in a cohort of patients with PHPT utilizing noninvasive imaging technology.

DESIGN

This was a prospective study evaluating patients consecutively diagnosed with PHPT in a single center over a 5-year period (2009-2013).

SETTING

The setting was a referral center.

PATIENTS

There were a total of 140 patients with PHPT (127 women [18 premenopausal and 109 postmenopausal] and 13 men; mean age, 63.2 ± 11 y).

MAIN OUTCOMES MEASURES

Main outcome measures were the prevalence of KS by abdominal ultrasound, osteoporosis by dual-energy x-ray absorptiometry (DXA) (lumbar spine, femoral neck, total hip, and distal 1/3 radius), and VFs by vertebral spine x-ray, with attention to those categorized as symptomatic or asymptomatic.

RESULTS

Fifty-five percent of all subjects had KS by ultrasound, 62.9% had osteoporosis by T-score at any site, and 35.1% had VFs by x-ray. There was no difference in the incidence of VFs and densitometric osteoporosis between symptomatic and asymptomatic patients (VFs, 34.4 vs 34.7%; osteoporosis by DXA, 59.4 vs 65.8%), whereas more KS were detected in symptomatic (78%) than asymptomatic (35.5%). Twenty-two percent of patients classified as asymptomatic at baseline without osteoporosis by DXA were found to have KS and/or VFs.

CONCLUSIONS

Nephrolithiasis and VFs are common in asymptomatic subjects with PHPT. The results provide evidence in support of recent recommendations that a more proactive approach be taken to detect silent bone and stone disease in asymptomatic PHPT.

Diagnosis and management of primary hyperparathyroidism--a scientific statement from the Department of Bone Metabolism, the Brazilian Society for Endocrinology and Metabolism

OBJECTIVE

To conduct a literature review on the diagnosis and management of primary hyperparathyroidism including the classical hipercalcemic form as well as the normocalcemic variant.

MATERIALS AND METHODS

This scientific statement was generated by a request from the Brazilian Medical Association (AMB) to the Brazilian Society for Endocrinology as part of its Clinical Practice Guidelines program. Articles were identified by searching in PubMed and Cochrane databases as well as abstracts presented at the Endocrine Society, Brazilian Society for Endocrinology Annual Meetings and the American Society for Bone and Mineral Research Annual Meeting during the last 5 years. Grading quality of evidence and strength of recommendation were adapted from the first report of the Oxford Centre for Evidence-based Medicine. All grades of recommendation, including "D", are based on scientific evidence. The differences between A, B, C and D, are due exclusively to the methods employed in generating evidence.

CONCLUSION

We present a scientific statement on primary hyperparathyroidism providing the level of evidence and the degree of recommendation regarding causes, clinical presentation as well as surgical and medical treatment.

Six-year follow-up of a characteristic osteolytic lesion in a patient with tumor-induced osteomalacia

OBJECTIVE

Tumor-induced osteomalacia is a rare paraneoplastic syndrome characterized by hypophosphatemia and inappropriately normal or low 1,25-dihydroxyvitamin D.

CLINICAL CASE

Here, we report a 6-year postoperative follow-up of a patient with oncogenic osteomalacia with a distinctive skeletal manifestation. The latter was characterized by an almost linear lytic lesion of a few millimeters with irregular borders, mainly involving the trabecular compartment but extending into cortical shell, located in the middle third of the right fibula. Six years after tumor resection, a sclerotic repair with a complete recovery was observed. Furthermore, we monitored a striking increase in bone mineral density throughout the observation period, reaching a peak of 73% over basal values at lumbar spine after 2 years; at total femur and radius, the peak was 47.5 and 4.6% respectively, after 4 years from tumor resection.

CONCLUSIONS

We report for the first time that an osteolytic lesion may be part of the skeletal involvement in tumor-induced osteomalacia.

Effect of a single oral dose of 600,000 IU of cholecalciferol on muscle strength: a study in young women

BACKGROUND

The effect of a single large oral dose of vitamin D on muscle function in young people with vitamin D deficiency has not been investigated so far.

AIM

We evaluated the effect of a single oral dose of 600,000 IU of cholecalciferol on muscle strength.

SUBJECTS AND METHODS

Eighteen young women with vitamin D deficiency received a single oral dose of 600,000 IU of cholecalciferol. We evaluated changes in maximal voluntary contraction (MVC) and speed of contraction (S) in response to cholecalciferol by using an hand held dynamometer at 3, 15, 30, 60 and 90 days, compared to baseline.

RESULTS

We observed no significant change in MVC and S values, a significant increase of 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] and a significant decrease in serum parathyroid hormone (PTH) (p<0.001 for all). A significant correlation was found between MVC and S and serum phosphorus (P) after supplementation (p<0.02 and p<0.05, respectively). Conversely, we observed no association between the parameters of muscle strength and 25(OH)D, ionized calcium (Ca2+), PTH and 1,25(OH)2D.

CONCLUSIONS

A single dose of 600,000 IU of cholecalciferol does not directly enhance handgrip strength in young women with vitamin D deficiency. More studies are needed on the indirect effect of the hormone on muscle.

The effect of parathyroidectomy on chronic constipation in patients affected by primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) is usually associated with chronic constipation; however, its prevalence is not defined by standardized criteria. The aim of the study was to evaluate both the prevalence of chronic constipation, defined by the standardized Rome diagnostic criteria III (Rome III) in PHPT, and the effect of parathyroidectomy (PTx). Fifty postmenopausal PHPT patients and 50 sex- and age-matched controls were studied. Each patient underwent mineral metabolism biochemical evaluation and completed a questionnaire and a 2-week diary card about bowel habits. PHPT patients were reevaluated after 6 months. According to Rome III, 40 % of PHPT patients had chronic constipation compared with 12 % of controls (p = 0.0002). The only difference between constipated PHPT patients (group A, n = 20) and those without constipation (group B, n = 30) was higher mean PTH values (79.9 ± 18.7 ng/l vs. 65.4 ± 26.0 ng/l; p = 0.03), which predicted the presence of constipation (p = 0.004, OR 1.059, CI 1.011-1.059). Forty percent of PHPT patients had undergone PTx. In group A, constipation was resolved in 80 % of patients after PTx compared to none of the same group who had not undergone PTx (p = 0.0007). In group B, 17.6 % of patients who had not undergone PTx became, after 6 months, constipated. According to Rome III, a higher prevalence of chronic constipation in PHPT patients was observed compared with controls. PTH levels predicted constipation. A significant reduction of chronic constipation was reported following successful surgery.

Parathyroidectomy eliminates arrhythmic risk in primary hyperparathyroidism, as evaluated by exercise test

OBJECTIVE

To investigate whether parathyroidectomy (PTx) reverses risk factors for arrhythmias related to the QT dynamic changes evaluated during bicycle ergometry exercise test (ET).

METHODS

Twenty-four postmenopausal women with primary hyperparathyroidism (PHPT) (mean age 60.08.4 years) and 30 sex- and age-matched controls underwent ET, echocardiography, and biochemical evaluation. The following stages were considered during ET: rest, peak exercise, and recovery. The patients were randomized to two groups: 12 underwent PTx (group A) and 12 were followed-up conservatively (group B). After 6 months, the patients were studied again.

RESULTS

Groups A and B showed no differences in mean baseline biochemical values, echocardiographic parameters, and QTC interval. PHPT patients showed an increased occurrence of ventricular premature beats (VPBS) during ET compared with controls (37.0 vs 6.6%, P=0.03). Serum calcium level was a predictor of VPBS (P=0.05). Mean value of QTC was in the normal range at baseline (Group A: 401±16.9; group B: 402.25±13.5 ms) but significantly lower than controls (417.8±25.1 ms, P<0.01). A negative correlation was found between QTc and calcium values (P=0.03). Physiological reduction of QTc interval from rest to peak exercise was not observed in PHPT patients before surgery. After PTx, group A had a significant reduction in VPBs compared with baseline (at baseline, 5 of 12 vs none of 12 patients after PTx, P=0.03) and a restored normal QT adaptation during ET. Group B showed no significant changes after a 6-month period.

CONCLUSIONS

PTx reduces the occurrence of VPBs and restored the QTc adaptation during ET.

Long-term bioavailability after a single oral or intramuscular administration of 600,000 IU of ergocalciferol or cholecalciferol: implications for treatment and prophylaxis

CONTEXT

We previously showed that a single high dose of oral (po) cholecalciferol (D₃) sharply increases serum 25-hydroxyvitamin D [25(OH)D].

OBJECTIVE

We evaluated the long-term bioavailability and metabolism of a single po or intramuscular (im) high dose of ergocalciferol (D₂) or D₃.

DESIGN

This was a prospective intervention study.

SETTING

The study was conducted in an ambulatory care setting.

PATIENTS

Participants were 24 subjects with hypovitaminosis D.

INTERVENTIONS

A single dose of 600,000 IU of po or im D₂ or D₃ was administered.

MAIN OUTCOME MEASURES

Serum 25(OH)D and 1,25-dihydroxyvitamin D [1,25(OH)₂D] were measured at baseline and at days 30, 60, 90, and 120 by RIA. Serum 1,25(OH)₂D₂, 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], 24,25-hydroxyvitamin D₂ [24,25(OH)D₂], and 24,25-hydroxyvitamin D₃ [24,25(OH)D₃] were measured by liquid chromatography-tandem mass spectrometry in a subgroup of patients receiving the po formulations.

RESULTS

The areas under the curve of 25(OH)D after D₃ were significantly higher than those after D₂ (P < .0001). Serum 25(OH)D basal difference significantly increased at day 30 with po D₂ and D₃ (P < .01 and P < .0001) and up to day 90 with po D₃ (P < .01). The im formulations produced a slow increased, and values peaked at day 120 relative to the other time points (P < .0001). We found a decrease in 1,25(OH)₂D at day 30 (P < .05) and up to day 120 (P < .001) and an increase in 1,25(OH)₂D₂ at day 30 (P < .01) and up to day 120 (P < .01) after po D₂. Oral D₂ and D₃ produced increases in 24,25(OH)D₂ and 24,25(OH)D₃, respectively, at day 30 (P < .001).

CONCLUSIONS

A po dose of 600,000 IU of D₂ or D₃ is initially more effective in increasing serum 25(OH)D than the equivalent im dose and is rapidly metabolized. Our RIA assay for 1,25(OH)₂D may not recognize 1,25(OH)₂D₂.

Effect of gender and geographic location on the expression of primary hyperparathyroidism

BACKGROUND

The effect of gender on the expression of primary hyperparathyroidism (PHPT) is not well characterized.

AIM

We therefore evaluated two Caucasian populations (US and Italian) of men and women with PHPT, matched for age and body mass index (BMI), in a cross-sectional retrospective observational study.

METHODS

We studied 74 US (23 men) and 126 Italian (42 men) patients evaluating main biochemical indices of the disease and bone mineral density (BMD) at the spine and proximal femur.

RESULTS

Mean serum calcium levels were higher both in Italian men compared to women (11.7 ± 1.22 mg/dl and 11.1 ± 0.83, p<0.01) and in Italian compared to US patients (11.3 ± 1.01 and 10.8 ± 0.58, p<0.001), with similar results for the serum ionized calcium. Mean serum PTH levels were not different either between the genders or between the countries. After controlling for BMI, the mean BMD at both the femoral neck and total hip in females US patients was significantly higher compared with Italian female patients.

CONCLUSION

Despite similar levels of circulating PTH, Italian patients have more pronounced effects of the disease as assessed by serum calcium and a more significant cortical involvement in women as assessed by BMD.

Arrhythmias in primary hyperparathyroidism evaluated by exercise test

BACKGROUND

Hypercalcemia induces arrhythmias and shortening of QT. The aim of this study was to investigate risk factors for occurrence of arrhythmias in patients with primary hyperparathyroidism (PHPT) during bicycle ergometer exercise test (ET).

METHODS

Thirty PHPT postmenopausal women (mean age, 60·9 ± 8·0 years) and 30, sex and age-matched, controls underwent ET, echocardiogram and mineral metabolism biochemical evaluation. The following stages were considered during ET: rest, peak exercise, recovery (early recovery, 2 and 10 min after peak exercise). QT was corrected with Bazett's formula (QTc).

RESULTS

Compared with controls, PHPT patients showed an increased occurrence of ventricular premature beats (VPBs) during ET (26·6% vs. 6·6%, P = 0·03). Being affected by PHPT predicted the onset of VPBs at peak exercise (P = 0·04) and recovery (P = 0·03), as shown by logistic regression analysis. In PHPT patients, serum calcium level was a predictor of VPBs at peak exercise (P = 0·05). QTc in patients with PHPT was in the normal range. Serum calcium level showed a negative correlation with QTc (P = 0·01) in whole sample. Compared with controls, PHTP patients had QTc significantly shorter for every stage of ET, except at peak exercise. Physiological reduction of QTc interval from rest to peak exercise was not seen in patients with PHPT, QTc at rest being the only predictor of QTc in every stage, as shown by multivariate regression analysis.

CONCLUSIONS

In patients with PHPT, an increased occurrence of VPBs and a different QTc adaptation during ET were observed and may represent risk factors for major arrhythmias.

Effects of strontium ranelate administration on calcium metabolism in female patients with postmenopausal osteoporosis and primary hyperparathyroidism

We investigated possible changes of parameters of calcium metabolism induced by strontium ranelate (SR). Twenty-three patients with postmenopausal osteoporosis (PO) and 14 with primary hyperparathyroidism (PHPT) were studied while taking 2 g/day of SR. Women with PO and 10 healthy age-matched control women were also daily supplemented with 1,000 mg calcium and 800 IU vitamin D. All subjects were studied at baseline and after 7 and 30 days; PO women and controls were also investigated at 180 and 360 days of treatment. Serum ionized calcium (iCa), phosphate (sP), magnesium, creatinine, 25-hydroxycholecalciferol (25[OH]D), 1,25-dihydroxycholecalciferol (1,25[OH](2)D), serum parathyroid hormone (PTH) were measured. In spot urine, we assessed calcium and phosphate over creatinine ratios (uCa/Cr, uP/Cr), calcium excretion (Ca ex) and renal phosphate threshold (TmP/GFR); in 24-h urine, calcium and magnesium over creatinine clearance ratios (CaCl/CrCl and MgCl/CrCl). In PO, SR administration was associated with a significant decrease of PTH and 1,25(OH)(2)D levels but an increase of sP (p < 0.001). SR also significantly increased Ca/Cr, Ca ex, and TmP/GFR in spot urine and CaCl/CrCl in both spot and 24-h urine (p = 0.004 to <0.001). In PHPT, SR significantly decreased iCa and increased sP, slightly modifying PTH, 25(OH)D, and 1,25(OH)(2)D values. Also in PHPT, Ca ex and CaCl/CrCl of spot and 24-h urine, as TmP/GFR, significantly increased (all p < 0.02). SR influenced the main parameters of calcium homeostasis, probably through the calcium-sensing receptor.

Metabolic changes following 500 μg monthly administration of calcidiol: a study in normal females

This study was performed to investigate the effect of monthly oral administration of 500 μg of calcidiol (25-hydroxyvitamin D(3)) for 4 months on both serum vitamin D levels and sequential changes of parameters of calcium metabolism; 18 normal women aged 24-72 years were investigated. There was a significant increase of serum 25(OH)D after the first administration; thereafter all values persisted significantly higher compared to the basal value (P < 0.001). Mean 1,25(OH)(2)D serum levels peaked at day 3 and then tended to stabilize following day 30. During the first month, all mean values observed following the initial administration were significantly higher than basal values. The first calcidiol dose produced a significant reduction of serum PTH levels (P < 0.001), which then remained constant over time. Concerning serum calcium and phosphorus, we were not able to demonstrate any significant change during the entire observation period. Considering the single values for both serum ionized and total calcium, the values of Ca(2+) exceeded upper limits of normal on only two occasions. Regarding biochemical markers of bone remodeling, mean changes of serum bone isoenzyme of alkaline phosphatase activity showed a significant trend to decrease, starting at day 30. No significant changes of serum CTX values were noted. Overall, 24-h urinary excretion of calcium did not change, seven values exceeding the threshold of 4 mg/kg body weight. Monthly administration of 500 μg of 25-hydroxyvitamin D(3) may be considered an alternative for vitamin D repletion, without any detrimental effect.

Acute and chronic effects of hypercalcaemia on cortical excitability as studied by 5 Hz repetitive transcranial magnetic stimulation

We designed the present study to disclose changes in cortical excitability in humans with hypercalcaemia, by delivering repetitive transcranial magnetic stimulation (rTMS) over the primary motor area (M1). In 22 patients with chronic hypercalcaemia related to primary hyperparathyroidism and 22 age-matched healthy subjects 5 Hz-rTMS was delivered at rest and during a sustained voluntary contraction of the target muscle. Changes in the resting motor threshold (RMT), motor evoked potential (MEP) amplitudes and cortical silent period (CSP) duration were measured and compared in patients and healthy controls. Two of the 22 patients were re-tested after parathyroidectomy when serum calcium had normalized. In a subgroup of healthy subjects, changes in the rTMS parameters were tested before and after acute hypercalcaemia. No significant difference between healthy normocalcaemic subjects and chronic hypercalcaemic patients was found in the RMT values and MEP amplitude and CSP duration evoked by the first stimulus of the trains. During the course of 5 Hz-rTMS trains, MEP size increased significantly less in patients with chronic hypercalcaemia than in healthy subjects, whereas the CSP duration lengthened to a similar extent in both groups. In the two patients studied after parathyroidectomy, rTMS elicited a normal MEP amplitude facilitation. Our findings indicate that acute hypercalcaemia significantly decreased the MEP amplitude facilitation. Given that 5 Hz-rTMS modulates cortical excitability through mechanisms resembling short-term synaptic enhancement, the reduction of MEP amplitude facilitation by hypercalcaemia may be related to Ca2+-dependent changes in synaptic plasticity.

Hyperparathyroidism

Hyperparathyroidism is due to increased activity of the parathyroid glands, either from an intrinsic abnormal change altering excretion of parathyroid hormone (primary or tertiary hyperparathyroidism) or from an extrinsic abnormal change affecting calcium homoeostasis stimulating production of parathyroid hormone (secondary hyperparathyroidism). Primary hyperparathyroidism is the third most common endocrine disorder, with the highest incidence in postmenopausal women. Asymptomatic disease is common, and severe disease with renal stones and metabolic bone disease arises less frequently now than it did 20-30 years ago. Primary hyperparathyroidism can be cured by surgical removal of an adenoma, increasingly by minimally invasive parathyroidectomy. Medical management of mild disease is possible with bisphosphonates, hormone replacement therapy, and calcimimetics. Vitamin D deficiency is a common cause of secondary hyperparathyroidism, particularly in elderly people. However, the biochemical definition of vitamin D deficiency and its treatment are subject to much debate. Secondary hyperparathyroidism as the result of chronic kidney disease is important in the genesis of renal bone disease, and several new treatments could help achieve the guidelines set out by the kidney disease outcomes quality initiative.

Diagnosis of asymptomatic primary hyperparathyroidism: proceedings of the third international workshop

OBJECTIVE

Asymptomatic primary hyperparathyroidism (PHPT) is a common clinical problem. The purpose of this report is to guide the use of diagnostic tests for this condition in clinical practice.

PARTICIPANTS

Interested professional societies selected a representative for the consensus committee and provided funding for a one-day meeting. A subgroup of this committee set the program and developed key questions for review. Consensus was established at a closed meeting that followed. The conclusions were then circulated to the participating professional societies.

EVIDENCE

Each question was addressed by a relevant literature search (on PubMed), and the data were presented for discussion at the group meeting.

CONSENSUS PROCESS

Consensus was achieved by a group meeting. Statements were prepared by all authors, with comments relating to accuracy from the diagnosis subgroup and by representatives from the participating professional societies.

CONCLUSIONS

We conclude that: 1) reference ranges should be established for serum PTH in vitamin D-replete healthy individuals; 2) second- and third-generation PTH assays are both helpful in the diagnosis of PHPT; 3) DNA sequence testing can be useful in familial hyperparathyroidism or hypercalcemia; 4) normocalcemic PHPT is a variant of the more common presentation of PHPT with hypercalcemia; 5) serum 25-hydroxyvitamin D levels should be measured and, if vitamin D insufficiency is present, it should be treated as part of any management course; and 6) the estimated glomerular filtration rate should be used to determine the level of kidney function in PHPT: an estimated glomerular filtration rate of less than 60 ml/min.1.73 m2 should be a benchmark for decisions about surgery in established asymptomatic PHPT.

Evolution of PTH assays

PTH metabolism is complex and the circulating forms include the intact 1-84 molecule as well as several carboxyl-terminal fragments. The first generation of PTH assays included several types of competitive assays, with specificities that spanned carboxyl, mid-region and amino-terminal portions of the molecule. The limitations of these assays and the methodological evolution led to the description of 2nd generation non-competitive immunometric assays for PTH in the late 80's, based on the recognition of the PTH molecule by two different antibodies, one directed against de amino-terminal and other against the carboxyl-terminal segments. The observation that in some circumstances "long" carboxyl-terminal segments were also measured by 2nd generation assays led to the development of 3rd generation assays based on amino-terminal specific antibodies that are specific for the first amino acids, measuring only the molecular forms that activate PTH1R. The practical and cost-benefit advantages of these assays are still debatable. The recent observation that carboxyl-terminal fragments of PTH have biological activity via a distinct receptor than PTH1R, points to the future need of more than one assay in order to evaluate parathyroid hormone function.

Unexpected Serum Parathyroid Hormone Profiles in Some Patients with Primary Hyperparathyroidism

Background: Third-generation parathyroid hormone (PTH) assays have been reported to measure only intact PTH(1–84), in contrast to second-generation assays, which also detect PTH(7–84) fragments. Higher PTH measurements were observed with third- than with second-generation PTH assays in a few patients with either severe primary hyperparathyroidism or parathyroid carcinoma.

Methods: We analyzed biological data [second- and third-generation PTH assays, 25-hydroxyvitamin D (25-OHD), calcium, and phosphate concentrations] obtained before and after surgery for 2 groups of patients selected from a large series of consecutive patients with primary hyperparathyroidism (PHPT): 7 female patients with surgically and histologically confirmed PHPT (group 1) and a matched group (group 2).

Results: For group 1 but not group 2, PTH concentrations measured by third-generation PTH assays before surgery were higher than those measured by the second-generation assays. Circulating 25-OHD, calcium, and phosphate concentrations were similar in both groups. In addition, PTH values measured with the third-generation PTH assays in group 1 decreased after surgery.

Conclusions: Our results confirm that third-generation PTH assays do not measure only PTH(1–84). The frequency of this unexpected finding of markedly lower PTH concentrations than previously reported was ∼5% in patients with PHPT without malignancy. We do not know whether the presence of this unexpected profile is predictive of malignancy.

Practical considerations in PTH testing

New knowledge concerning PTH biology have accumulated during the past few years. The finding that the so-called "intact" PTH assays measure a "non-1-84" PTH fragment in addition to full-length PTH has led to the development of new assays. These new assays, which were initially thought to measure 1-84 PTH only, have been shown to recognize also another PTH species called "amino-PTH". As the various names given to the different assay methods are highly confusing, there is a need for a simplified nomenclature. A simple way would be to identify the older "intact" PTH assays as second-generation assays and the new assays (Whole, CAP, BioIntact) as third-generation assays. Although of considerable potential interest for the comprehension of PTH physiology, the third-generation PTH assays have not yet proved to be superior to the second-generation assays in clinical practice. There is thus currently no recommendation to switch from the second-generation to the third-generation assays in clinical practice, or to use a ratio derived from the concommitent measurement of PTH with both assay-generation. Because second- and third-generation PTH assays are usually highly correlated, significant differences in the clinical information provided by these methods are unlikely. However, our opinion is that more definitive bone biopsy studies in dialyzed patients selected according to their bone- and calcium-related treatment are still needed to reach a consensus. Finally, we have proposed that PTH reference values should be established in healthy subjects with a normal vitamin D status. This supposes that 25OHD is measured in the reference population beforehand, and that the subjects with vitamin D insufficiency are eliminated from the reference group. Although more complicated than the usual way to establish normative data, we have shown that it decreases the upper limit of normal by 25-35%, enhancing thus the diagnostic sensitivity for hyperparathyroidism without a decrease in specificity.

First- and second-generation immunometric PTH assays during treatment of hyperparathyroidism with cinacalcet HCl

BACKGROUND

First-generation immunometric assays for "intact" parathyroid hormone (iPTH) also measure large N-terminally truncated PTH fragments, whereas second-generation assays, such as the "bio-intact" PTH (biPTH) assay, measure only full-length biologically active PTH(1-84). This study compared iPTH and biPTH assays during cinacalcet treatment in subjects with secondary HPT receiving dialysis.

METHODS

Four hundred and ten subjects were enrolled in a 26-week randomized, double-blind, placebo-controlled trial of oral cinacalcet (or placebo), 30 to 180 mg once daily, and efficacy was assessed using biPTH and iPTH assays.

RESULTS

Compared with control treatment, cinacalcet improved the management of secondary HPT. Both biPTH and iPTH decreased by 38%+/- 3% during weeks 13 to 26 in the cinacalcet group; biPTH increased by 23%+/- 4% and iPTH increased by 9.5%+/- 3% in the control group (P < 0.001). Fifty-six percent of cinacalcet subjects and 10% of control subjects had a > or = 30% reduction in biPTH, and 61% and 11%, respectively, had a > or = 30% reduction in iPTH. Significant correlations between biPTH and iPTH levels were observed throughout the study. Both assays correlated similarly with bone-specific alkaline phosphatase levels. The ratio of biPTH to iPTH was maintained at 56% +/- 1% after treatment in both treatment groups. Increasing serum calcium levels were associated with a decreasing ratio of biPTH to (iPTH-biPTH).

CONCLUSION

These data show that PTH can be monitored with either iPTH or biPTH assays during therapy with cinacalcet, and that cinacalcet therapy does not exert a major influence on the ratio between PTH(1-84) and large, N-terminally truncated PTH fragments.

Assay-Specific Decision Limits for Two New Automated Parathyroid Hormone and 25-Hydroxyvitamin D Assays

Background: The recent development of nonradioactive automated assays for serum parathyroid hormone (PTH) and 25-hydroxyvitamin D (25OHD) has made measurement of these two hormones possible in many laboratories. In this study, we compared two new assays for PTH and 25OHD adapted on an automated analyzer, the LIAISON®, with two manual immunoassays used worldwide.

Methods: We studied 228 osteoporotic patients, 927 healthy individuals, 38 patients with primary hyperparathyroidism, and 167 hemodialyzed patients. Serum PTH was measured with the Allegro® and the LIAISON assays, and 25OHD was measured with DiaSorin RIA and the LIAISON assay. Regression analysis was used to calculate decision thresholds for the LIAISON assays that were equivalent to those of the Allegro PTH and DiaSorin 25OHD assays.

Results: The 25OHD concentrations obtained with the LIAISON assay and the RIA in osteoporotic patients were well correlated (r = 0.83; P &lt;0.001). Regression and Bland–Altman analyses suggested that the LIAISON 25OHD assay reads lower than the DiaSorin RIA at low concentrations but higher at high concentrations. However, the cutoff (50 nmol/L) used in our laboratories to define vitamin D insufficiency with the DiaSorin RIA is applicable to the LIAISON 25OHD assay. In 927 healthy individuals, the 3rd–97th percentile intervals were 3–80 ng/L and 13–151 nmol/L for the LIAISON PTH and 25OHD concentrations, respectively. However, 506 individuals (54.6%) were vitamin D-insufficient; we therefore considered only the 421 individuals with a LIAISON 25OHD &gt;50 nmol/L as eligible for the reference population for the LIAISON PTH assay. In this group, the 3rd–97th percentile interval for LIAISON PTH was 3–51 ng/L. Considering upper reference limits of 46 and 51 ng/L for the Allegro and LIAISON assays, respectively, the frequency of above-normal PTH concentrations in patients with primary hyperparathyroidism was similar in both assays. Regression analysis between serum PTH measured by the Allegro and LIAISON assays in 167 hemodialyzed patients and the corresponding Bland–Altman analysis of these data suggest that the LIAISON PTH assay tends to read higher than the Allegro assay at low concentrations but lower at high concentrations (&gt;300 ng/L).

Conclusions: Because clinical decision limits for both PTH and 25OHD should be assay specific, we propose equivalences between these assays and two manual assays used worldwide. These assay-specific decision limits should help potential users of the LIAISON PTH and 25OHD assays.

Hyperparathyroïdie et ostéoporose

INTRODUCTION

In patients with primary hyperparathyroidism, a definite diagnosis is the first step in the management strategy and relies on appropriately selected and carefully interpreted laboratory tests. Parathyroid hormone assays are being increasingly performed as part of the routine evaluation of osteoporosis.

CURRENT KNOWLEDGE AND KEY POINTS

In this setting, laboratory tests are often consistent with primary hyperparathyroidism but should be interpreted with caution.

FUTURE PERSPECTIVES

Bone mineral density measurements are useful for assessing the impact of primary hyperparathyroidism. The recommended bone mineral density cutoffs for selecting patients requiring parathyroidectomy were lowered in 2003, and the number of surgically treated patients has increased as a result. Parathyroidectomy remains the treatment of choice given the low mortality associated with this procedure and the absence of pharmacological alternatives suitable for long-term use.