Aplastic osteodystrophy without aluminum: the role of "suppressed" parathyroid function

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.

Hyporesponsiveness or resistance to the action of parathyroid hormone in chronic kidney disease

Secondary hyperparathyroidism (SHPT) is an integral component of the chronic kidney disease-mineral and bone disorder (CKD-MBD). Many factors have been associated with the development and progression of SHPT but the presence of skeletal or calcemic resistance to the action of PTH in CKD has often gone unnoticed. The term hyporesponsiveness to PTH is currently preferred and, in this chapter, we will not only review the scientific timeline but also some of the molecular mechanisms behind. Moreover, the presence of resistance to the biological action of PTH is not unique in CKD since resistance to other hormones has also been described ("uremia as a receptor disease"). This hyporesponsiveness carries out important clinical implications since it explains, at least partially, not only the progressive nature of the pathogenesis of CKD-related PTH hypersecretion and parathyroid hyperplasia but also the increasing prevalence of adynamic bone disease in the CKD population. Therefore, we underline the importance of PTH control in all CKD stages, but not aiming to completely normalize PTH levels since a certain degree of SHPT may represent an adaptive clinical response. Future studies at the molecular level, i.e. on uremia or the recent description of the calcium-sensing receptor as a phosphate sensor, may become of great value beyond their significance to explain just the hyporesponsiveness to PTH in CKD.

Bone Quality in CKD Patients: Current Concepts and Future Directions - Part I

BACKGROUND

There is ample evidence that patients with CKD have an increased risk of osteoporotic fractures. Bone fragility is not only influenced by low bone volume and mass but also by poor microarchitecture and tissue quality. More emphasis has been given to the quantitative rather than qualitative assessment of bone health, both in general population and CKD patients. Although bone mineral density (BMD) is a very useful clinical tool in assessing bone strength, it may underestimate the fracture risk in CKD patients. Serum and urinary bone biomarkers have been found to be reflective of bone activities and predictive of fractures independently of BMD in CKD patients. Bone quality and fracture risk in CKD patients can be better assessed by utilizing new technologies such as trabecular bone score and high-resolution imaging studies. Additionally, invasive assessments such as bone histology and micro-indentation are useful counterparts in the evaluation of bone quality.

SUMMARY

A precise diagnosis of the underlying skeletal abnormalities in CKD patients is crucial to prevent further bone loss and fractures. We must consider bone quantity and quality abnormalities for management of CKD patients. Here in this part I, we are focusing on advances in bone quality diagnostics that are expected to help in proper understanding of the bone health in CKD patients.

KEY MESSAGES

Assessment of bone quality and quantity in CKD patients is essential. Both noninvasive and invasive techniques for the assessment of bone quality are available.

Hyporesponsiveness or resistance to the action of parathyroid hormone in chronic kidney disease

Secondary hyperparathyroidism (SHPT) is an integral component of the chronic kidney disease-mineral and bone disorder (CKD-MBD). Many factors have been associated with the development and progression of SHPT but the presence of skeletal or calcemic resistance to the action of PTH in CKD has often gone unnoticed. The term hyporesponsiveness to PTH is currently preferred and, in this chapter, we will not only review the scientific timeline but also some of the molecular mechanisms behind. Moreover, the presence of resistance to the biological action of PTH is not unique in CKD since resistance to other hormones has also been described ("uremia as a receptor disease"). This hyporesponsiveness carries out important clinical implications since it explains, at least partially, not only the progressive nature of the pathogenesis of CKD-related PTH hypersecretion and parathyroid hyperplasia but also the increasing prevalence of adynamic bone disease in the CKD population. Therefore, we underline the importance of PTH control in all CKD stages, but not aiming to completely normalize PTH levels since a certain degree of SHPT may represent an adaptive clinical response. Future studies at the molecular level, i.e. on uremia, or the recent description of the calcium-sensing receptor as a phosphate sensor, may become of great value beyond their significance to explain just the hyporesponsiveness to PTH in CKD.

Chronic Kidney Disease-Mineral and Bone Disorders: Pathogenesis and Management

The key players of the chronic kidney disease-mineral and bone disorders (CKD-MBD) are calcium, phosphate, PTH, FGF23, and the vitamin D hormonal system. The progressive reduction of kidney function greatly modifies the tightly interrelated mechanisms that control these parameters. As a result, important changes occur in the bone and mineral hormonal axis, leading to changes in bone turnover with relevant consequences in clinical outcomes, such as decrease in bone mass with increased bone fragility and bone fractures and increased vascular and valvular calcification, also with great impact in the cardiovascular outcomes. So far, the knowledge of the mineral and bone disorders in CKD and the increased variety of efficacious therapies should lead to a better prevention and management of CKD-MBD.

Surgical Management of Secondary Hyperparathyroidism

Secondary hyperparathyroidism (SHPT) affects a majority of patients with chronic kidney disease (CKD) of stage 3 or worse. Despite the development of calcimimetics and their effectiveness in treating SHPT, many patients continue to fail medical management and should be referred to a parathyroid surgeon. In this narrative review, we summarize the indications for surgical referral, preoperative planning, intraoperative strategies to guide resection, and postoperative management. In the absence of universal guidelines, it can be difficult to determine when it is appropriate to make this referral. The majority of studies evaluating parathyroidectomy (PTX) for SHPT use the criteria of parathyroid hormone level (PTH) >800 pg/ml with hypercalcemia and/or hyperphosphatemia, which may be accompanied by symptoms such as bone pain and pruritis that can improve after surgery. Although the reported utility of the various imaging modalities (i.e., 99m-technetium-sestamibi scintigraphy with computed tomography [SPECT/CT], CT, or ultrasound) is highly variable in SHPT, SPECT/CT appears to be the most sensitive. Intraoperatively, PTH monitoring is effective in predicting long-term cure of SHPT but not in predicting hypoparathyroidism. Ectopic and supernumerary parathyroid glands are common in these patients and are often implicated in persistent or recurrent disease. Postoperatively, patients are at risk of severe hypocalcemia and hungry bone syndrome requiring close monitoring and replenishment.

High Prevalence of Hyperparathyroidism among Peritoneal Dialysis Patients: A Review of 176 Patients

Objectives

Parathyroid dysfunction continues to produce significant morbidity in dialysis patients. Since the introduction of low calcium dialysate for peritoneal dialysis (PD), no large studies have been done to determine the prevalence of parathyroid dysfunction in these patients. This study was done to assess the prevalence of parathyroid disease in the PD population and to determine the risk factors associated with this dysfunction.

Design

We analyzed data on 176 patients who received PD at a single center between August 1998 and February 1999. Clinical data, laboratory variables related to parathyroid function, and data pertaining to dialysis treatment and weekly drug dosing were obtained for each patient on two different occasions, approximately 3 months apart. Variables predictive of the development of parathyroid dysfunction were calculated by univariate and multivariate logistic regression analysis.

Results

Two-thirds of the patients surveyed had an abnormal intact parathyroid hormone (iPTH) level: 47% had an iPTH level more than three times normal, the mean was 54.6 ± 35.4 pmol/L; 23% had an iPTH value below the upper limit of normal, here the mean was 3.6 ± 1.8 pmol/L. Diabetic patients had lower iPTH levels (22.2 ± 28.4 pmol/L) than nondiabetics (33.9 ± 34.8 pmol/L) ( p = 0.02). On multivariate regression analysis, we found that age, duration of dialysis, Kt/V, serum bicarbonate, and serum ionized calcium levels did not significantly affect parathyroid function. Hyperphosphatemia was the only factor that was associated with the development of secondary hyperparathyroidism in this study population ( p = 0.029).

Conclusion

There is a high prevalence of hyperparathyroidism in the current PD population. Phosphate control is suboptimal and hyperphosphatemia is an independent risk factor for the development of hyperparathyroidism.

Serum Magnesium Concentration is An Independent Predictor of Parathyroid Hormone Levels in Peritoneal Dialysis Patients

Background

Parathyroid hormone (PTH) is a cardinal factor in the pathogenesis of bone disease in the dialysis population. The spectrum of renal osteodystrophy has been reported to have changed during the past years, and adynamic bone disease has emerged as the most common bone disorder in these patients. Continuous ambulatory peritoneal dialysis (CAPD) is considered a risk factor for the development of this condition, and furthermore, the adynamic bone lesion is associated with a state of relative hypoparathyroidism (hypo-PTH). Calcium, vitamin D, and phosphorus play a key role in the control of parathyroid gland function in uremic patients. However, magnesium may also be able to modulate PTH secretion in a way similar to calcium.

Objective

The aims of this study were (1) to analyze the serum Mg concentration in a large group of CAPD patients, (2) to study the relationship between serum Mg and PTH levels, and (3) to investigate whether this relationship is independent of other factors, such as calcium, phosphorus, and calcitriol, that regulate parathyroid function.

Patients and Methods

We studied 51 stable patients, aged 23 – 77 years, under maintenance CAPD for more than 6 months (range 8 – 48 months). Calcium carbonate was used as a phosphate binder in all patients, and 9 subjects also received aluminum hydroxide. No patient had been previously treated with vitamin D. Biochemical parameters were prospectively evaluated over 6 months, and the mean values were computed.

Results

The mean serum Mg was 1.08 ± 0.19 mmol/L, and hypermagnesemia, defined as a Mg level higher than 1.01 mmol/L, was found in 30 patients (59%). Thirty-one subjects (60%) had an intact PTH (iPTH) level lower than 120 pg/mL and were diagnosed as having relative hypo-PTH. Except for the values of iPTH and alkaline phosphatase, the only difference between the two groups was the serum Mg concentration, which was significantly higher in patients with hypo-PTH (1.16 ± 0.15 mmol/L vs 0.91 ± 0.14 mmol/L; p < 0.001). Furthermore, iPTH levels were lower in patients with hypermagnesemia than in subjects with normal serum Mg (69 ± 49 pg/mL vs 190 ± 89 pg/mL, p < 0.001). There was a significant correlation between serum Mg and PTH levels ( r = –0.70, p < 0.01). After controlling for the effect of other variables by partial correlation analysis, a significant positive association between P and PTH ( r = 0.25, p < 0.05), and a negative relationship between Mg and PTH ( r = –0.57, p < 0.001) were evident. A forward stepwise multiple regression analysis showed that only P and Mg predicted PTH values (multiple r = 0.59, p < 0.001).

Conclusions

Hypermagnesemia and hypoparathyroidism are frequent in CAPD patients. There is a significant inverse relationship between serum Mg concentration and iPTH levels. Furthermore, this association is independent of the most important factors regulating parathyroid gland function (calcium, phosphorus, and calcitriol). These results suggest that hypermagnesemia may have a suppressive effect on PTH synthesis and/or secretion. Therefore, elevated serum Mg levels may play a role in the pathogenesis of adynamic bone disease.

Long Term Dialysis with Low-Calcium Solution (1.0 Mmol/L) in Capd: Effects on Bone Mineral Metabolism

Objective

Peritoneal dialysate solutions with conventionally high-calcium (Ca) concentrations (1.75 mmol/L) are now widely replaced by solutions with a lower, more physiological calcium content to prevent hypercalcemia in patients treated with oral calcium-containing phosphate binders and/or calcitriol. While there is still debate on how far the dialysate calcium should be lowered (1.25 mmol/L or less), little information is available concerning the effects of a long-term treatment with low-calcium solutions on secondary hyperparathyroidism and bone mineral metabolism in general.

Design

A prospective, randomized, controlled multicenter study to compare the effects of low-calcium (LCa, dialysate calcium 1.0 mmol/L) versus standard calcium dialysate solution (SCa, dialysate calcium 1.75 mmol/L)on bone mineral metabolism in continuous ambulatory peritoneal dialysis (CAPD) patients over 2 years of treatment.

Setting

Nephrology and dialysis units of primary and tertiary hospitals in Germany and Switzerland.

Patients

All CAPD patients in the participating centers between 18 and 80 years of age, stable on CAPD for at least 1 month, free of aluminum bone disease or prior parathyroidectomy were invited to enter the study. Sixty-four patients could be randomly allotted to LCa (n = 35) or SCa (n = 29) treatment in a 2-year protocol; 34 finished the study as planned.

Interventions

Calcium carbonate (CaCO3) was given as oral phosphate binder to maintain serum phosphate <2.0 mmol/L. If hypercalcemia supervened, CaCO3 was exchanged stepwise for aluminium hydroxide (AI(OH)3)’ until normocalcemia was obtained. Patients received calcitriol (0.25 μg/day per os) if parathyroid hormone (PTH) exceeded the upper limit of normal by a factor of 2 or more.

Main Outcome Measures

We assessed total and ionized serum calcium, phosphate, serum aluminum, alkaline phosphatase, osteocalcin, PTH (intact molecule), and phosphate binder intake at regular intervals. Measurements of bone mineral density and hand skeleton x-rays were obtained at the start and after 6 months and 2 years, respectively.

Results

With LCa, mean total and ionized serum calcium levels were within the normal range (total Ca: 2.0 2.6 mmol/L; ionized Ca: 1.19–1.32 mmol/L), but throughout the treatment period were significantly lower than with SCa. The incidence of hypercalcemia (>2.8 mmol/L) was three times higher in patients on SCa, despite the significantly higher amount of AI(OH)3 and less CaCO3 given in this group. In parallel, serum aluminum increased with SCa throughout the study, whereas it was slowly decreasing with LCa. Median PTH levels remained stable at about two times the upper limit of normal over the 2 years of study with LCa. However, 23% of the patients on LCa developed severe hyperparathyroidism, with PTH levels exceeding ten times the upper limit of normal compared to only 10.3% of the patients on SCa. With SCa, median PTH decreased towards near normal levels. Alkaline phosphatase and serum osteocalcin correlated positively with PTH levels. Bone mineral density was in the lower normal range in both groups a n d remained unchanged at the end of the study. Skeletal x-ray films showed only minor alterations in very few patients in both groups with no correlation to serum PTH or treatment modality.

Conclusion

In CAPD patients low-calcium dialysate solutions can be used successfully over prolonged periods of time with stable control of serum calcium. The risk of hypercalcemia resulting from calcium-containing phosphate binders and the need to use aluminum-containing phosphate binders is markedly diminished. However, there is a certain risk that severe secondary hyperparathyroidism with long-term LCa therapy will develop, even if normocalcemia is maintained. Thus, LCa dialysis requires closeand continuous monitoring of PTH and bone metabolism.

Management of Renal Osteodystrophy in Peritoneal Dialysis Patients

The term “renal osteodystrophy” encompasses all forms of metabolic bone disease found in dialysis patients. The primary approach to the treatment of renal osteodystrophy in peritoneal dialysis (PD) patients is similar to that in hemodialysis patients. However, the increased prevalence of adynamic bone histology, together with the difficulty in judging calcium balance, the inability to practicably give intravenous vitamin D, and the clearance of vitamin D and parathyroid hormone via dialysate require a different therapeutic approach in PD compared to hemodialysis patients. Clearly, more comparative studies of new agents are needed to find the optimal approach to achieving the K/DOQI guidelines in PD patients. The unique aspects of the approach to renal osteodystrophy in PD patients are the focus of this review.

Bone Mineral Density: Serum Markers of Bone Turnover and Their Relationships in Peritoneal Dialysis

Background

The usefulness of bone mass measurements and bone turnover markers to estimate the risk of fracture and the type of underlying renal osteodystrophy are not well established in patients on peritoneal dialysis (PD).

Objective

To assess bone mass using total and regional bone densitometry in a group of patients on PD and to determine if serum markers of bone turnover identify patients with low bone mass.

Methods

Bone densitometry was studied by dual-energy x-ray absorptiometry (DEXA), and bone turnover using several serum markers, in 65 patients on PD. Bone mass was classified as normal, osteopenic, or osteoporotic according to World Health Organization criteria based on bone mineral density (BMD) T scores.

Results

T scores in the osteopenia range were present at the lumbar spine (LS) in 44.6% (45% of men and 44.4% of women) of patients and at the femoral neck (FN) in 56.9% (55% of men and 58% of women). T scores in the osteoporosis range were present at the LS in 13.8% of patients (10% of men and 15.5% of women) and at the FN in 21.5% (30% of men and 17.7% of women). Patients with BMD T scores in the osteoporosis range at both regions had increased serum intact parathyroid hormone (iPTH) levels compared to patients in the osteopenic/normal range. Bone mineral content in the whole skeleton (TBMC) correlated negatively with iPTH ( r = –0.34) and with total time on dialysis ( r = –0.26); in multivariate analysis, only iPTH correlated negatively with TBMC ( B = –0.26, p = 0.03). No correlations were found between the other bone markers and BMD T scores at the FN or LS. There were no significant differences in absolute BMD or BMD T scores at the LS or FN between patients with and patients without fractures.

Conclusions

BMD T scores in the osteopenia/osteoporosis range were observed at the LS in 58.4% of these patients on PD and at the FN in 78.4%. TBMC correlated negatively with iPTH. There were no correlations between markers of bone turnover and bone mass measurements at the two skeletal regions, although patients with BMD T scores in the osteoporosis range had increased serum iPTH levels. Bone mass measurements were not different between patients with and patients without fractures.

Normal or Low Initial PTH Levels are not a Predictor of Morbidity/Mortality in Patients Undergoing Chronic Peritoneal Dialysis

♦ Objective

During the past few decades, the pattern of bone disease in uremic patients has changed significantly. There has been an increase in the number of patients with normal or low initial parathyroid hormone (PTH) levels, particularly in patients on chronic peritoneal dialysis (CPD). Previous authors have described a higher prevalence of bone pain, microfractures, and fractures, and higher mortality among these patients. The aim of this study was to determine the incidence, morbidity, and mortality of patients who had a low or normal intact PTH (iPTH) level when they started CPD.

♦ Design

We reviewed the records of 251 patients in our program that started CPD during the past 5 years (January 1996 – December 2000). Clinical data, laboratory variables, medication, and dialysis parameters/dose were available at every clinic visit (approximately every 4 weeks). Intact PTH was used to express parathyroid function; values 3 times higher than the upper limit of normal (ULN) were assumed to be optimal. Variables predictive of the development of parathyroid dysfunction were calculated by univariate and multivariate logistic regression analysis.

♦ Results

Of the patients who started CPD, 15.5% had iPTH values below the ULN (7.6 pmol/L), and an additional 29.5% had an iPTH of less than 3 times the ULN ( i.e., between 7.6 and 22.8 pmol/L). We call these two groups of patients the normal/low initial iPTH group. During the follow-up period (3 – 63 months), we found a trend toward increasing iPTH levels. By the end of the study period, 61.2% of those with normal/low initial iPTH remained in the normal/low iPTH range, and 38.8% had converted to a group with an iPTH range higher than 22.8 pmol/L. The patients who converted their iPTH grouping were younger, fewer of them were diabetics ( p = not significant), and they were more frequently on low calcium dialysate ( p < 0.05). Hyperphosphatemia was an independent risk factor for subsequent iPTH changes during the course of continuous ambulatory PD treatment. All patients in the normal/low iPTH groups had a low prevalence of bone fractures (3.5%). Also, patients who remained in the normal/low iPTH group at the end of the follow-up period did not have more fractures than those who converted to the hyperparathyroid group (3.8% vs 3.1%). We found no differences in bone fractures between patients with iPTH levels below 22.8 and those with levels above 22.8 pmol/L (3.5% vs 5.4%), nor were there differences in patient and technique survival between these two groups.

♦ Conclusion

Normal/low initial iPTH is a frequent finding among patients starting CPD. Serum phosphorus was an independent risk factor for subsequent iPTH changes during the course of CPD treatment. Use of low calcium dialysate was significantly higher in patients who converted their iPTH into the high iPTH range. Very few patients with low/normal iPTH had bone-related symptoms (pain and fractures), and their morbidity and mortality did not differ from those patients with a high initial iPTH level.

Calcium Concentration in the Capd Dialysate: What is Optimal and is There a Need to Individualize?

Objective

To evaluate risk/benefit of various continuous ambulatory peritoneal dialysis (CAPD) dialysate calcium concentrations.

Data Sources

A review of the literature on the effects of various CAPD dialysate Ca concentrations on plasma Ca, plasma phosphate, plasma parathyroid hormone (PTH), doses of calcium carbonate, doses of vitamin D analogs, and requirements of aluminum-containing phosphate binders.

Study Selection

Eleven studies of nonselected CAPD patients, and 13 studies of CAPD patients with hypercalcemia were reviewed.

Results

In nonselected CAPD patients, treatment with a reduced dialysate Ca concentration (1.00, 1.25, or 1.35 mmol/L) improved the tolerance to calcium carbonate and/or vitamin D metabolites and reduced the need for Al-containing phosphate binders. When using dialysate Ca 1.25 or 1.35 mmol/L, the initial decrease of plasma Ca and increase of PTH could easily be reversed with an immediate adjustment of the treatment. After 3 months, stable plasma Ca and PTH levels could be maintained using only monthly investigations. In patients with hypercalcemia and elevated PTH levels, treatment with dialysate Ca concentrations below 1.25 mmol/L implied a considerable risk for the progression of secondary hyperparathyroidism. When hypercalcemia was present in combination with suppressed PTH levels, a controlled increase of PTH could be obtained with a temporary discontinuation of vitamin D and/or a reduction of calcium carbonate treatment in combination with a dialysate Ca concentration of 1.25 or 1.35 mmol/L.

Conclusion

Most CAPD patients can be treated effectively and safely with a reduced dialysate Ca concentration of 1.35 or 1.25 mmol/L. Treatment with dialysate Ca concentrations below 1.25 mmol/L should not be used. A small fraction of patients with persistent hypocalcemia need treatment with high dialysate Ca, such as 1.75 mmol/L.

Serum Markers of Low-Turnover Bone Disease in Mexican Children with Chronic Kidney Disease Undergoing Dialysis

Background

The frequency of low-turnover bone disease (LTBD) in patients with chronic kidney disease (CKD) has increased in past years. This change is important because LTBD is associated with bone pain, growth delay, and higher risk for bone fractures and extraosseous calcifications. LTBD is a histological diagnosis. However, serum markers such as parathyroid hormone (PTH) and calcium levels offer a noninvasive alternative for diagnosing these patients.

Objective

To describe the prevalence of LTBD in pediatric patients with renal failure undergoing some form of renal replacement therapy, using serum calcium and intact PTH levels as serum markers.

Methods

In this cross-sectional study, 41 children with CKD undergoing dialysis treatment (31 on continuous ambulatory peritoneal dialysis and 10 on hemodialysis) were included. There were no inclusion restrictions with respect to gender, cause of CKD, or dialysis modality. The children were studied as outpatients. The demographic data, CKD course, time on dialysis, phosphate-binding agents, and calcitriol prescription were registered, as well as weight, height, Z-score for height, linear growth rate, and Z-score for body mass index. Serum calcium, phosphorus, aluminum, PTH, alkaline phosphatase, osteocalcin, glucose, creatinine, urea, cholesterol, and triglycerides were measured.

Results

There were 20 (48.8%) children with both PTH <150 pg/mL and corrected total calcium >10 mg/dL who were classified as having LTBD[(+)]; the remaining 21 (51.2%) children were classified as having no LTBD[(–)]. The LTBD(+) patients were younger (11.2 ± 2.7 vs 13.2 ± 2.4 years, p < 0.01) but they had no differences regarding Z-scores for height. Linear growth in 6 months was less than expected in both groups (-0.15 ± 0.23 cm/month), but the difference between expected and observed growth was higher in the LTBD(+) group (-0.24 ± 0.14 vs –0.07 ± 0.28 cm/mo, p < 0.03). LTBD(+) patients also had lower serum creatinine (8.69± 2.75 vs 11.19 ± 3.17 mg/dL, p < 0.01), higher serum aluminum levels [median (range) 38.4 (9 – 106) vs 28.1 (9 – 62) μg/L, p < 0.05], and lower systolic blood pressure (112.0 ± 10.3 vs 125.0 ±12.9 mmHg, p < 0.015) and diastolic blood pressure (76.0 ± 9.7 vs 84.5 ± 8.2 mmHg, p < 0.017). A significant correlation was found between PTH and alkaline phosphatase ( r = 0.68, p < 0.001), but not between PTH and aluminum.

Conclusion

The LTBD(+) biochemical profile was found in 48.8% of the children and was associated with impaired linear growth. Aluminum contamination, evidenced by higher serum aluminum levels, may have had a pathogenic role in these disorders. Higher systolic and diastolic blood pressure levels may be related to higher serum PTH levels.

Klotho: a humeral mediator in CSF and plasma that influences longevity and susceptibility to multiple complex disorders, including depression

Klotho is a hormone secreted into human cerebrospinal fluid (CSF), plasma and urine that promotes longevity and influences the onset of several premature senescent phenotypes in mice and humans, including atherosclerosis, cardiovascular disease, stroke and osteoporosis. Preliminary studies also suggest that Klotho possesses tumor suppressor properties. Klotho's roles in these phenomena were first suggested by studies demonstrating that a defect in the Klotho gene in mice results in a significant decrease in lifespan. The Klotho-deficient mouse dies prematurely at 8-9 weeks of age. At 4-5 weeks of age, a syndrome resembling human ageing emerges consisting of atherosclerosis, osteoporosis, cognitive disturbances and alterations of hippocampal architecture. Several deficits in Klotho-deficient mice are likely to contribute to these phenomena. These include an inability to defend against oxidative stress in the central nervous system and periphery, decreased capacity to generate nitric oxide to sustain normal endothelial reactivity, defective Klotho-related mediation of glycosylation and ion channel regulation, increased insulin/insulin-like growth factor signaling and a disturbed calcium and phosphate homeostasis accompanied by altered vitamin D levels and ectopic calcification. Identifying the mechanisms by which Klotho influences multiple important pathways is an emerging field in human biology that will contribute significantly to understanding basic physiologic processes and targets for the treatment of complex diseases. Because many of the phenomena seen in Klotho-deficient mice occur in depressive illness, major depression and bipolar disorder represent illnesses potentially associated with Klotho dysregulation. Klotho's presence in CSF, blood and urine should facilitate its study in clinical populations.

Reduction of Dialysate Calcium Level Reduces Progression of Coronary Artery Calcification and Improves Low Bone Turnover in Patients on Hemodialysis

Exposure to high Ca concentrations may influence the development of low-turnover bone disease and coronary artery calcification (CAC) in patients on hemodialysis (HD). In this randomized, controlled study, we investigated the effects of lowering dialysate Ca level on progression of CAC and histologic bone abnormalities in patients on HD. Patients on HD with intact parathyroid hormone levels ≤300 pg/ml receiving dialysate containing 1.75 or 1.50 mmol/L Ca (n=425) were randomized to the 1.25-mmol/L Ca (1.25 Ca; n=212) or the 1.75-mmol/L Ca (1.75 Ca; n=213) dialysate arm. Primary outcome was a change in CAC score measured by multislice computerized tomography; main secondary outcome was a change in bone histomorphometric parameters determined by analysis of bone biopsy specimens. CAC scores increased from 452±869 (mean±SD) in the 1.25 Ca group and 500±909 in the 1.75 Ca group (P=0.68) at baseline to 616±1086 and 803±1412, respectively, at 24 months (P=0.25). Progression rate was significantly lower in the 1.25 Ca group than in the 1.75 Ca group (P=0.03). The prevalence of histologically diagnosed low bone turnover decreased from 85.0% to 41.8% in the 1.25 Ca group (P=0.001) and did not change in the 1.75 Ca group. At 24 months, bone formation rate, trabecular thickness, and bone volume were higher in the 1.25 Ca group than in the 1.75 Ca group. Thus, lowering dialysate Ca levels slowed the progression of CAC and improved bone turnover in patients on HD with baseline intact parathyroid hormone levels ≤300 pg/ml.

Adynamic bone disease: from bone to vessels in chronic kidney disease

Adynamic bone disease (ABD) is a well-recognized clinical entity in the complex chronic kidney disease (CKD)-mineral and bone disorder. Although the combination of low intact parathyroid hormone (PTH) and low bone alkaline phosphatase levels may be suggestive of ABD, the gold standard for precise diagnosis is histomorphometric analysis of tetracycline double-labeled bone biopsies. ABD essentially is characterized by low bone turnover, low bone volume, normal mineralization, and markedly decreased cellularity with minimal or no fibrosis. ABD is increasing in prevalence relative to other forms of renal osteodystrophy, and is becoming the most frequent type of bone lesion in some series. ABD develops in situations with reduced osteoanabolic stimulation caused by oversuppression of PTH, multifactorial skeletal resistance to PTH actions in uremia, and/or dysregulation of Wnt signaling. All may contribute not only to bone disease but also to the early vascular calcification processes observed in CKD. Various risk factors have been linked to ABD, including calcium loading, ageing, diabetes, hypogonadism, parathyroidectomy, peritoneal dialysis, and antiresorptive therapies, among others. The relationship between low PTH level, ABD, increased risk fracture, and vascular calcifications may at least partially explain the association of ABD with increased mortality rates. To achieve optimal bone and cardiovascular health, attention should be focused not only on classic control of secondary hyperparathyroidism but also on prevention of ABD, especially in the steadily growing proportions of diabetic, white, and elderly patients. Overcoming the insufficient osteoanabolic stimulation in ABD is the ultimate treatment goal.

Healthcare use and costs before and after parathyroidectomy in patients on dialysis

BACKGROUND

Parathyroidectomy (PTX) is often performed in dialysis patients when medical treatment fails to control secondary hyperparathyroidism (SHPT). PTX is viewed by many as a cost-containing measure for patients who have been treated with vitamin D analogs and calcimimetics. Yet, information about health resource utilization and costs before and after PTX is limited.

METHODS

This retrospective cohort study used professional service and pharmacy claims to identify subjects on dialysis undergoing PTX from 1/1/2008-12/31/2010. Only subjects with at least six months of information before and after PTX were considered. Subjects with primary hyperparathyroidism or kidney transplant were excluded. Prescription use, physician encounters, and surgical complications were compared during the six months immediately before and after PTX.

RESULTS

The mean (SD) age of the 181 study subjects was 51 (15) years; 59% female; and 80% insured by Medicare. Overall, the percentage of patients receiving medications to manage altered mineral metabolism increased from 67% before to 79% after PTX. Specifically, oral vitamin D use increased, while the utilization of cinacalcet decreased resulting in mean (SD) monthly medication charges decreasing from $486 (507) to $226 (288) (p < 0.01). The mean (SD) number of physician encounters rose from 15 (14) before to 21 (22) per 6 months after PTX (p < 0.01) resulting in the corresponding increase in mean (SD) monthly charges from $1531 (2150) to $1965 (3317) (p = 0.08). Hypocalcemia was the predominant diagnosis recorded for post-surgical physician encounters occurring in 31% of all subjects; 84% of hypocalcemic episodes were managed in acute care facilities.

CONCLUSIONS

The cost of medications to manage SHPT decreased after PTX largely due to reduction in cinacalcet use, whereas vitamin D use increased likely to manage hypocalcemia. The frequency and cost of physician encounters, especially in acute care settings, were higher in the 6 months after PTX attributable largely to episodes of severe hypocalcemia. Overall, the reduction in prescription costs during the 6 months after PTX is outweighed by the higher costs associated with physician care.

Mineral and bone disease in black african hemodialysis patients: a report from senegal

BACKGROUND

Chronic kidney disease related mineral and bone disease (CKD-MBD) is a worldwide challenge in hemodialysis patients. In Senegal, number of dialysis patients is growing but few data are available about their bone disorders.

OBJECTIVES

To describe patterns of CKD-MBD in Senegalese dialysis patients.

PATIENTS AND METHODS

We performed a cross-sectional study including patients from three dialysis centres in Senegal. Diagnosis of different types of CKD-MBD relied on clinical, biological and radiological data collected from medical records in dialysis.

RESULTS

We included 118 patients and 79 of them presented CKD-BMD (prevalence of was 66.9 %). Mean age of CKD-MBD patients was 47.8 ± 15.7 years (16-81 years) and sex-ratio (Male/Female) was 1.15. Secondary hyperparathyroidism was the most frequent disorder (57 patients) followed by adynamic bone disease (21 patients) and osteomalacia (1 patients). The main clinical manifestations were bone pain (17.5% of cases), pruritus (36.8% of cases) and pathological fractures (2.5% of cases). Bone biopsy was not available. Valvular and peripheral vascular calcification were present in 24.5% and 21.2% of patients respectively. Management of CKD-MBD included optimization of dialysis, calcium bicarbonate, sevelamer, vitamin D analogues and calcimimetics. The NKF/DOQI recommended levels of serum calcium, phosphate and parathormone PTH were not achieved in one third of patients. Six patients presented major cardiovascular events during their dialysis period.

CONCLUSIONS

CKD-MBD are frequent in Senegalese hemodialysis patients and they are dominated by high turn-over disease. Clinical and biological manifestations are unspecific and accurate diagnoses are often difficult in absence of histomorphometry. Treatment is suboptimal for many patients in a context of limited resources.

Vitamin d and stage 5 chronic kidney disease: a new paradigm?

Vitamin D receptor agonists (VDRA) are currently recommended for the treatment of secondary hyperparathyroidism in stage 5 CKD. They are considered to be contraindicated in the presence of low or normal (for a dialysis patient) levels of PTH due to the risk of developing adynamic bone disease, with consequent vascular calcification. However, these recommendations are increasingly at odds with the epidemiological evidence, which consistently shows a large survival advantage for patients treated with low-dose VDRAs, regardless of plasma calcium, phosphate, or PTH. A large number of pleiotropic effects of vitamin D have been described, including inhibition of renin activity, anti-inflammation, and suppression of vascular calcification stimulators and stimulation of vascular calcification inhibitors present in the uremic milieu. Laboratory studies suggest that a normal cellular vitamin D level is necessary for normal cardiomyocyte and vascular smooth muscle function. While pharmacological doses of VDRA can be harmful, the present evidence suggests that the level of 1,25-dihydroxycholecalciferol should also be more physiological in stage 5 CKD, and that widespread use of low-dose VDRA would be beneficial. A randomized controlled trial to test this hypothesis is warranted.

Mineral and bone disorders in chronic kidney disease and end-stage renal disease patients: new insights into vitamin D receptor activation

Progressive loss of kidney function leads to reduced production of calcitriol (1,25-dihydroxyvitamin D; active vitamin D) and an imbalance in serum calcium (Ca) and phosphorus (P) levels, which are associated with progression of renal failure as well as increased rates of cardiovascular (CV) events and mortality. In addition, multifactorial hypocalcemia and resistance to parathyroid hormone (PTH) can lead to prolonged and excessive synthesis and secretion of PTH, eventually leading to development of secondary hyperparathyroidism and renal osteodystrophy. These changes associated with chronic kidney disease (CKD), extending beyond bone and related biochemical abnormalities, have prompted the development of the term CKD–mineral and bone disorder to describe its systemic nature. Excessive P loading, among other factors, will promote vascular calcification (VC), and PTH production will affect bone remodeling. Although administration of calcitriol increases serum Ca levels and decreases PTH, it is also associated with elevated Ca × P product. Therefore, compounds that selectively activate vitamin D receptors (VDR activators), potentially reducing Ca–P toxicity and distinctly affecting pathogenic mechanisms of VC, might enhance CV and renal protection, increase the vitamin D therapeutic window, and thus provide a significant clinical benefit. Moreover, selective VDR activators have been associated with improvement in survival, at least among dialysis patients. Thus, selective VDR activators should be considered a novel and interesting approach to enhance the standard of care in CKD patients.

The Effect of Paricalcitol on Vascular Calcification and Cardiovascular Disease in Uremia: Beyond PTH Control

Secondary hyperparathyroidism is a systemic disorder that associates with bone and cardiovascular disease, including arterial calcification. Treatment with calcitriol, the active form of vitamin D, reduces parathyroid hormone levels, but may result in elevations in serum calcium and phosphorus, increasing the risk of vascular calcification in dialysis patients. New vitamin D receptor activators (VDRAs) have been developed and investigated with the rationale to treat high serum PTH levels, with a reduced risk of hypercalcemia and hyperphosphatemia. Paricalcitol is a selective VDRA that suppresses PTH secretion with minimal increases on serum calcium and phosphate. Moreover, paricalcitol prevents vascular calcification in experimental models of renal failure, compared with calcitriol.

Bone histomorphometry: a concise review for endocrinologists and clinicians

Bone histomorphometry is a quantitative histological examination of an undecalcified bone biopsy performed to obtain quantitative information on bone remodeling and structure. Labeling agents taken before the procedure deposit at sites of bone formation allowing a dynamic analysis. Biopsy is indicated to make the diagnosis of subclinical osteomalacia, to characterize the different forms of renal osteodystrophy and to elucidate cases of unexplained skeletal fragility. Bone histomorphometric parameters are divided into structural and remodeling subgroups, with the latter being subdivided into static and dynamic categories. Metabolic bone disorders such as osteomalacia, hyperparathyroidism, hypothyroidism, osteoporosis and renal osteodystrophy display different histomorphometric profiles. Antiresorptive and anabolic drugs used for the treatment of osteoporosis also induce characteristic changes in the bone biopsy. Bone histomorphometry is an important research tool in the field of bone metabolism and provides information that is not available by any other investigative approach.

A Comparison of Sevelamer Hydrochloride with Calcium Acetate on Biomarkers of Bone Turnover in Hemodialysis Patients

OBJECTIVE

To evaluate the influence of sevelamer hydrochloride and calcium acetate on biomarkers of bone turnover in patients with hyperphosphatemia receiving hemodialysis.

METHODS

In this prospective, open-label, randomized, active-controlled study, 70 patients (38 men and 32 women) with hyperphosphatemia (serum phosphorus level >6.0 mg/dL) underwent a two-week washout period and were randomly selected to receive sevelamer hydrochloride (n = 37) or calcium acetate (n = 33) for eight weeks. Changes in serum levels of intact parathyroid hormone (iPTH), alkaline phosphatase (Alk-P), phosphorus, and calcium were measured and compared.

RESULTS

After eight weeks of treatment, calcium acetate lowered iPTH levels significantly more than sevelamer hydrochloride did (-178.0 vs. -69.0 pg/mL, p = 0.0019). Levels of Alk-P were significantly elevated in patients given sevelamer hydrochloride compared with levels in those given calcium acetate treatment (24.09 vs. 7.45 U/L, p = 0.0014). Changes in serum phosphorus levels did not differ between sevelamer hydrochloride (-1.93 mg/dL) and calcium acetate (-2.5 mg/dL) at the end of the study (p = 0.0514). Changes in the calcium and phosphorous product did not significantly differ between the sevelamer-hydrochloride group (-18.06 mg2/dL2) and the calcium-acetate group (-19.05 mg2/dL2, p = 0.6764). Fifteen patients (45.5%) treated with calcium acetate had hypercalcemia (serum-adjusted calcium level >10.5 mg/dL); the rate was significantly higher than that of patients treated with sevelamer (five [13.5%] of 37, p = 0.0039).

CONCLUSION

Treatment with sevelamer hydrochloride had the advantage of maintaining stable iPTH levels and elevating Alk-P levels while lowering serum phosphorus levels and calcium-phosphorous product.

Critical issues of PTH assays in CKD

Measurement of bioactive parathyroid hormone (PTH) is essential for the optimal management of secondary hyperparathyroidism and its associated bone disorders in chronic kidney disease (CKD) patients. For this purpose, three generations of increasingly specific PTH assays have been developed over the last 4 decades. To date, however, only second-generation PTH assays are most widely used, although these have been shown to cross-react with large PTH fragments having a partially preserved N-structure, mostly PTH(7-84). The newly developed third-generation PTH assays are believed to be the most specific means of measuring PTH(1-84), but their clinical utility remains debatable. More recently, these latter assays have also been shown to react with a new N-form of PTH, which has been identified in patients with severe hyperparathyroidism and parathyroid carcinoma. Progressive research in this area has advanced our understanding considerably regarding the circulating molecular forms of PTH and their pathophysiological roles in bone abnormalities associated with CKD. However, developing an ideal PTH assay continues to be difficult because of key issues such as the reliability of PTH as a surrogate marker for bone turnover, practicality of employing third-generation PTH assays, and unknown biological implications of N-PTH and other PTH fragments. Further research exploring these issues is mandatory to understand and optimally manage parathyroid disorders and bone abnormalities in CKD patients.

Role of bone biopsy in stages 3 to 4 chronic kidney disease

Secondary hyperparathyroidism develops relatively early in chronic kidney disease as a consequence of impaired phosphate, calcium, and vitamin D homeostasis. The disease state in chronic kidney disease, which includes the histologic features of bone disease, defined as renal osteodystrophy, and the hormonal and biochemical disturbances, have recently been redefined as a disease syndrome and is referred to as "chronic kidney disease-mineral and bone disorder." As chronic kidney disease progresses, specific histologic disturbances in the bone develop, which may or may not be predictable from the biochemical and hormonal changes that are associated with chronic kidney disease. In addition, patients may have had underlying bone disease before developing kidney failure or may have been treated with agents that will alter the classical pathologic findings of the bones in chronic kidney disease and their relation to parathyroid hormone. Thus, in stage 5 chronic kidney disease, bone biopsy with quantitative histomorphometric analysis is considered the gold standard in the diagnosis of renal osteodystrophy. In contrast to stage 5 chronic kidney disease, there are very few data on the histologic changes in bone in earlier stages of chronic kidney disease. There also is no adequate information on the etiopathogenesis of bone disease in stages 3 and 4 chronic kidney disease. Thus, because biochemical data cannot predict bone pathology in stages 3 and 4 chronic kidney disease, bone biopsy should be used to define these bone changes and to allow appropriate therapeutic approaches.

Hyperphosphatemia of chronic kidney disease

Observational studies have determined hyperphosphatemia to be a cardiovascular risk factor in chronic kidney disease. Mechanistic studies have elucidated that hyperphosphatemia is a direct stimulus to vascular calcification, which is one cause of morbid cardiovascular events contributing to the excess mortality of chronic kidney disease. This review describes the pathobiology of hyperphosphatemia that develops as a consequence of positive phosphate balance in chronic kidney disease and the mechanisms by which hyperphosphatemia acts on neointimal vascular cells that are stimulated to mineralize in chronic kidney disease. The characterization of hyperphosphatemia of chronic kidney disease as a distinct syndrome in clinical medicine with unique disordered skeletal remodeling, heterotopic mineralization and cardiovascular morbidity is presented.

Higher strength lanthanum carbonate provides serum phosphorus control with a low tablet burden and is preferred by patients and physicians: a multicenter study

BACKGROUND AND OBJECTIVES

Management of hyperphosphatemia, a predictor of mortality in chronic kidney disease, is challenging. Nonadherence to dietary phosphate binders, in part, contributes to uncontrolled serum phosphorus levels. This phase IIIb trial assessed the efficacy of increased dosages (3000 to 4500 mg/d) of reformulated lanthanum carbonate (500-, 750-, and 1000-mg tablets) in nonresponders to dosages of up to 3000 mg/d.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This 8-wk study with a 4-mo open-label extension enrolled 513 patients who were undergoing maintenance hemodialysis. Patients who achieved serum phosphorus control at week 4 with <or=3000 mg/d lanthanum carbonate entered cohort A; nonresponders were randomly assigned to receive 3000, 3750, or 4500 mg/d (cohort B). The primary outcome measure was the control rate for predialysis serum phosphorus levels at the end of week 8, among patients in cohort B.

RESULTS

At the end of week 4, 54% of patients achieved serum phosphorus control at dosages <or=3000 mg/d administered as one tablet per meal. Among patients who entered cohort B, control rates of 25, 38, and 32% for patients who were randomly assigned to 3000, 3750, or 4500 mg/d lanthanum carbonate, respectively, were achieved, with no increase in adverse events. Patients and physicians reported significantly higher levels of satisfaction with reformulated lanthanum carbonate compared with previous phosphate binders, partly because of reduced tablet burden with higher dosage strengths. Physicians and patients also expressed a preference for lanthanum carbonate over previous medication.

CONCLUSIONS

Reformulated lanthanum carbonate is an effective phosphate binder that may reduce daily tablet burden.

Variation in serum and plasma PTH levels in second-generation assays in hemodialysis patients: a cross-sectional study

BACKGROUND

Previous reports show that parathyroid hormone (PTH) concentrations may vary widely depending on the assay used to assess PTH. In this cross-sectional study, we aim to determine the usefulness of standardizing blood handling for optimal interpretation of PTH in patients with chronic kidney disease.

STUDY DESIGN

Diagnostic test study.

SETTING & PARTICIPANTS

Predialysis blood was sampled in 34 long-term hemodialysis patients at a single academic medical center.

INDEX TEST

PTH was measured by using 6 different automated second-generation assays (Elecsys, Advia Centaur, LIAISON, Immulite, Architect, and Access assays), 3 blood specimen types (serum, EDTA plasma, and citrate plasma), and 2 consecutive days of measurement (after thawing and 18 hours later with samples having been let at room temperature).

REFERENCE TEST

None.

RESULTS

A mixed statistical analysis model showed that the nature of the assay (P < 0.001) and nature of the blood sample (P < 0.001) significantly influenced variability in PTH concentrations, whereas day of measurement (day 1 or 2) did not (P = 0.5). Most PTH variability was caused by observations (96.8%), then manufacturer's kit (2.5%), and last, specimen type (0.7%). PTH concentrations measured in citrate plasma were lower with every assay method used than those observed in serum or EDTA plasma. The interaction between manufacturer and specimen type was of moderate statistical significance (P = 0.04). To evaluate the potential clinical consequence of PTH measure variability, we classified patients according to Kidney Disease Outcomes Quality Initiative cutoff values (PTH < 150 pg/mL; PTH, 150 to 300 pg/mL; and PTH > 300 pg/mL). Overall, statistical classification agreement was moderate to high for comparison between assays and high to very high between different blood samples and between days of measurement. However, we found that up to 11 of 34 patients were classified in different categories with some assays (LIAISON versus Architect) and up to 7 of 34 in different categories with different blood specimen type (citrate plasma versus serum [corrected] in LIAISON assay).

LIMITATIONS

This is a cross-sectional study that used single lots of reagents. There currently is no reference method for the measurement of PTH and no recombinant PTH standard for PTH assay.

CONCLUSION

PTH variability caused by the nature of the assay and/or blood specimen type is large enough to potentially influence clinical decision making. A specified collection method therefore should be used for PTH measurements. In routine practice, we recommend serum PTH over EDTA or citrate plasma.

Adynamic bone in patients with chronic kidney disease

Adynamic bone in patients with chronic kidney disease (CKD) is a clinical concern because of its potential increased risk for fracture and cardiovascular disease (CVD). Prevalence rates for adynamic bone are reportedly increased, although the variance for its prevalence and incidence is large. Differences in its prevalence are largely attributed to classification and population differences, the latter of which constitutes divergent groups of elderly patients having diabetes and other comorbidities that are prone to low bone formation. Most patients have vitamin D deficiency and the active form, 1,25-dihydroxyvitamin D, invariably decreases to very low levels during CKD progression. Fortunately, therapy with vitamin D receptor activators (VDRAs) appears to be useful in preventing bone loss, in part, by its effect to stimulate bone formation and in decreasing CVD morbidity, and should be considered as essential therapy regardless of bone turnover status. Future studies will depend on assessing cardiovascular outcomes to determine whether the risk/reward profile for complications related to VDRA and CKD is tolerable.

Renal Osteodystrophy in Peritoneal Dialysis: Special Considerations

Bone disease is one of the most challenging complications in patients with chronic kidney disease. Today, it is considered to be part of a complex systemic disorder manifested by disturbances of mineral metabolism and vascular calcifications called chronic kidney disease – mineral bone disorder (CKD-MBD).

The term renal osteodystrophy is reserved to define the specific bone lesion in CKD-MBD, whose spectrum ranges from high turnover to low turnover disease. Phosphate retention, decreased serum calcium, and 1,25-dihydroxy vitamin D synthesis are involved in the pathogenesis of high bone turnover. However, the various therapeutic approaches (calcium supplements, phosphate binders, and vitamin D metabolites, among others), the renal replacement modality (hemodialysis or continuous ambulatory peritoneal dialysis), and the types of patients to whom dialysis is offered (more patients who are diabetic or older, or both) may influence the evolution of the bone disorder. As a result, recent studies have reported a greater prevalence of adynamic forms of renal osteodystrophy, especially in diabetic and peritoneal dialysis patients.

The present article reviews, for patients treated with peritoneal dialysis, the pathophysiologic mechanisms involved in the evolution and perpetuation of this bone disease and the therapeutic modalities for treating and preventing adynamic bone.

Vitamin D and Peritoneal Dialysis

Chronic kidney disease – mineral and bone disorder (CKD–MBD) is a cause of significant morbidity and mortality in patients with long-standing kidney disease. Management of secondary hyperparathyroidism includes the use of phosphorus-binding agents and treatment with activated vitamin D compounds, better referred to as vitamin D receptor agonists (VDRAs). In an effort to maximize the therapeutic response while reducing the adverse effects of calcitriol, the naturally synthesized hormone, the use of intravenous administration and several selective VDRAs have been developed. Recently, oral preparations of these selective VDRAs have become available, enabling their use in the peritoneal dialysis (PD) population. The present report reviews the data concerning the use of oral VDRAs for the treatment of hyperparathyroidism in PD patients. The data, although limited, appear to support the use of oral paricalcitol as the VDRA in PD patients. In addition, traditional teaching focuses only on therapy with VDRAs, ignoring vitamin D replacement in CKD stage 5. However, given the potential benefits of calcidiol (25-OH-D) repletion and the rampant 25-OH-D deficiency in the PD population, our opinion is that screening for and treating that deficiency should extend beyond early CKD and also include PD patients.

K/DOQI-recommended intact PTH levels do not prevent low-turnover bone disease in hemodialysis patients

The guidelines proposed by the Kidney Disease Outcomes Quality Initiative (K/DOQI) suggested that intact parathyroid hormone (iPTH) should be maintained in a target range between 150 and 300 pg ml(-1) for patients with stage 5 chronic kidney disease. Our study sought to verify the effectiveness of that range in preventing bone remodeling problems in hemodialysis patients. We measured serum ionized calcium and phosphorus while iPTH was measured by a second-generation assay. Transiliac bone biopsies were performed at the onset of the study and after completing 1 year follow-up. The PTH levels decreased within the target range in about one-fourth of the patients at baseline and at the end of the study. The bone biopsies of two-thirds of the patients were classified as showing low turnover and a one-fourth showed high turnover, the remainder having normal turnover. In the group achieving the target levels of iPTH 88% had low turnover. Intact PTH levels less than 150 pg ml(-1) for identifying low turnover and greater than 300 pg ml(-1) for high turnover presented a positive predictive value of 83 and 62%, respectively. Our study suggests that the iPTH target recommended by the K/DOQI guidelines was associated with a high incidence of low-turnover bone disease, suggesting that other biochemical markers may be required to accurately measure bone-remodeling status in hemodialysis patients.