Bio-Intact Parathyroid Hormone and Intact Parathyroid Hormone in Hemodialysis Patients With Secondary Hyperparathyroidism Receiving Intravenous Calcitriol Therapy

Comparison of Intact PTH and Bio-Intact PTH Assays Among Non-Dialysis Dependent Chronic Kidney Disease Patients

BACKGROUND

The third-generation bio-intact parathyroid hormone (PTH) (1-84) assay was designed to overcome problems associated with the detection of C-terminal fragments by the second-generation intact PTH assay. The two assays have been compared primarily among dialysis populations. The present study evaluated the correlations and differences between these two PTH assays among patients with chronic kidney disease (CKD) stages 3 to 5 not yet on dialysis.

METHODS

Blood samples were collected from 98 patients with CKD stages 3 to 5. PTH concentrations were measured simultaneously by using the second-generation - PTH intact-STAT and third-generation bio-intact 1-84 PTH assays. Other serum biomarkers of bone mineral disorders were also assessed. CKD stage was calculated by using the CKD-Epidemiology Collaboration (EPI) formula.

RESULTS

Serum bio-intact PTH concentrations were strongly correlated but significantly lower than the intact PTH concentrations (r=0.963, P<0.0001). This finding was consistent among CKD stages 3 to 5. PTH concentrations by both assays (intact and bio-intact PTH) positively correlated with urea (r=0.523, r=0.504; P=0.002, respectively), phosphorus (r=0.532, r=0.521; P<0.0001, respectively) and negatively correlated with blood calcium (r=-0.435, r=-0.476; P<0.0001, respectively), 25(OH) vitamin D, (r=-0.319, r=-0.353; respectively, P<0.0001) and the estimated glomerular filtration rate (r=-0.717, r=-0.688; P<0.0001, respectively).

CONCLUSIONS

Among patients with CKD stages 3 to 5 not on dialysis, the bio-intact PTH assay detected significantly lower PTH concentrations compared with intact PTH assay. Additional studies that correlate the diagnosis and management of CKD mineral and bone disorders with bone histomorphometric findings are needed to determine whether bio-intact PTH assay results are better surrogate markers in these early stages of CKD.

Comparison between a second and a third generation parathyroid hormone assay in hemodialysis patients

OBJECTIVE

Third generation parathyroid hormone (PTH) assays are new generation assays that do not recognize the PTH7-84 fragment whereas second generation assays detect both PTH1-84 and PTH7-84 fragments. Despite the excellent correlation between both assays in chronic renal failure (CRF) subjects, the mean PTH levels are typically 50% lower with the third compared to the second generation assays. The assessment of third generation PTH assays has not been extensively studied in hemodialysis subjects. The purpose of our study was to compare a third generation PTH assay to a second generation one in a population of hemodialysis subjects.

MATERIALS AND METHODS

92 haemodialysis subjects (36 women and 56 men) with a mean age of 67±12.9 years were included in this study. Anthropometric and clinical parameters (Body Mass Index (BMI) and blood pressure) were measured. Second and third generation PTH assays (Cis biomedical and Diasorin respectively) were performed in each subject. In addition, the following biochemical tests were measured: 25-hydroxyvitamin D (25-(OH)D), 1,25-hydroxyvitamin D (1,25-(OH)2D), crosslaps and alkaline phosphatase.

RESULTS

The mean second and third generation PTHs are respectively 211±205 pg/ml and 151±164 pg/ml. The mean third generation PTH values are 28.4% lower compared to the second generation ones. Both methods are strongly correlated (r=0.923, p<0.001). This correlation persisted without any significant difference after controlling for gender, age, BMI and Blood Pressure. However, the difference between both methods increases when baseline PTH increases. Each of the second and third generation method is significantly correlated with hemodialysis duration (p<0.01), crosslaps (p<0.001), alkaline phosphatase (p<0.05), but not with age, BMI, Blood Pressure, 25-(OH)D or 1,25-(OH) 2D levels.

CONCLUSION

Our results show that both second and third generation PTH methods are strongly correlated in hemodialysis patients mainly when PTH values are low. However, the difference between both methods increases when PTH values are high. More research is needed to establish which method is the gold standard when PTH values are high.

Response of different PTH assays to therapy with sevelamer or CaCO3 and active vitamin D sterols

Amino-terminally truncated parathyroid hormone (PTH) fragments are detected to differing degrees by first- and second-generation immunometric PTH assays (PTH-IMAs), and acute changes in serum calcium affect the proportion of these fragments in circulation. However, the effect of chronic calcium changes and different vitamin D doses on these PTH measurements remains to be defined. In this study, 60 pediatric dialysis patients, aged 13.9 +/- 0.7 years, with secondary hyperparathyroidism were randomized to 8 months of therapy with oral vitamin D combined with either calcium carbonate (CaCO(3)) or sevelamer. Serum phosphorus levels did not differ between groups. Serum calcium levels rose from 9.3 +/- 0.1 to 9.7 +/- 0.1 mg/dl during CaCO(3) therapy (p < 0.01 from baseline) but remained unchanged during sevelamer therapy. In the CaCO(3) and sevelamer groups, baseline serum PTH levels (1st PTH-IMA; Nichols Institute Diagnostics, San Clemente, CA) were 964 +/- 75 and 932 +/- 89 pg/ml, and levels declined to 491 +/- 55 and 543 +/- 59 pg/ml, respectively (nonsignificant between groups). Patients treated with sevelamer received higher doses of vitamin D than those treated with CaCO(3). The PTH values obtained by first- and second-generation PTH-IMAs correlated closely throughout therapy and the response of PTH was similar to both PTH-IMAs, despite differences in serum calcium levels.

Combined therapy with cinacalcet and low doses of vitamin D sterols in patients with moderate to severe secondary hyperparathyroidism

BACKGROUND

Adequate control of all four KDOQI biochemical targets for chronic kidney disease, bone and mineral disorder (CKD-MBD), which include parathyroid hormone (PTH), calcium (Ca), phosphorus (P) and Ca x P, remains difficult and is accomplished in <6% of patients receiving haemodialysis. The objective of the current study was to determine whether treatment with cinacalcet combined with low doses of vitamin D sterols improves control of both PTH and Ca x P among haemodialysis patients with secondary hyperparathyroidism (sHPT).

METHODS

This multicentre, open-label study enrolled haemodialysis subjects (N = 444) with moderate to severe sHPT (mean serum biPTH > 160-430 pg/mL) (approximately iPTH 300-800 pg/mL or ng/L). Cinacalcet was titrated sequentially (30-180 mg/day) during an 8-week dose-titration phase to achieve biPTH <or=160 pg/mL (approximately iPTH 300 pg/mL or ng/L) and efficacy was assessed over 8 weeks. At week 2 of the study, subjects receiving vitamin D sterols had doses reduced to the equivalent of 2 mcg of paricalcitol three times a week or 6 mcg/week. Among the efficacy endpoints were the proportion of subjects with mean biPTH <or=160 pg/mL (approximately iPTH 300 pg/mL or ng/L), with mean Ca x P <or=55 mg(2)/dL(2) (4.4 mmol(2)/L(2)) and with both simultaneously during the assessment phase.

RESULTS

The majority of subjects (n = 375) reached the assessment phase of the study and were included in efficacy analyses; 39 subjects withdrew due to adverse events. Sixty-two percent of subjects achieved the biPTH target, 83% achieved the Ca x P target and 54% reached both targets. Treatment reduced biPTH by 35% (P < 0.0001), calcium by 11% (P < 0.0001), phosphorus by 7% (P < 0.0001) and Ca x P by 17% (P < 0.0001). The proportion of subjects with values for biPTH, for Ca x P and for both biPTH and Ca x P within the target range during the assessment phase did not differ between subjects who received cinacalcet together with vitamin D sterols, and those who received cinacalcet alone.

CONCLUSION

Among subjects with moderate to severe sHPT undergoing haemodialysis, combined therapy with cinacalcet and low doses of vitamin D sterols improved achievement of the biochemical targets for CKD-MBD recommended by the KDOQI guidelines.

Regulation of parathyroid function in chronic kidney disease (CKD)

In chronic kidney disease (CKD), several abnormalities in bone and mineral metabolism develop in the majority of patients. The parathyroid plays a very important role in regulating bone and mineral metabolism; thus, control of parathyroid function is one of the main targets of the management of CKD-mineral and bone disorder (CKD-MBD). In the development of secondary hyperparathyroidism, it has recently been suggested that fibroblast growth factor 23 (FGF23) plays a crucial role, both as a phosphaturic factor and as a suppressor of active vitamin D (1,25D) production in the kidney. FGF23 is originally secreted to prevent hyperphosphatemia in CKD, but this occurs at the expense of low 1,25D and hyperparathyroidism ("trade-off" hypothesis revisited). Furthermore, recent data suggest that FGF23 could be another useful marker for the prognosis of hyperparathyroidism, because a high serum level may reflect the cumulative dose of vitamin D analogues previously administered. We have also demonstrated that severe hyperparathyroidism was associated with the production and secretion of a new form of parathyroid hormone (PTH) molecule, which can be detected by third-generation assays for PTH, but not by the second-generation assays. For the regression of already established nodular hyperplasia, the more advanced type of parathyroid hyperplasia, it is certainly necessary, in the near future, to develop new agents that specifically induce apoptosis in parathyroid cells. Until such agents are developed, prevention and early recognition of nodular hyperplasia is mandatory for the effective and safe management of hyperparathyroidism in CKD.

Overproduction and Secretion of a Novel Amino-Terminal Form of Parathyroid Hormone from a Severe Type of Parathyroid Hyperplasia in Uremia

Measurement of bioactive parathyroid hormone (PTH) is essential for optimal management of bone abnormalities in dialysis patients. This can be accomplished by PTH measurements using third-generation PTH assays, which detect more or less of the first six amino acids of the PTH structure. Such assays do not detect non-(1-84) PTH fragments, such as human PTH (7-84), which are recognized by the second-generation PTH assays that use a detection antibody that recognizes an epitope within the 13-34 region of the PTH structure. Therefore, third-generation PTH results are expected to be lower than those that are obtained with second-generation PTH assays. Rare exceptions to this rule have been reported for patients with severe primary hyperparathyroidism or parathyroid cancer. Sera and gland extracts were analyzed from a dialysis patient with high bone turnover disease and with surprising higher PTH levels by a third-generation assay than by a second-generation assay. This finding normalized after the surgical removal of an enlarged gland with a single nodule, an advanced type of nodular hyperplasia. HPLC fractionation of sera and gland extracts revealed the overproduction and secretion of a PTH molecule with an intact amino-terminus structure distinct from (1-84) PTH. This form of PTH was readily detectable by third-generation PTH assays but was poorly reactive in second-generation PTH assays. Therefore, parathyroid glands with advanced uremic nodular hyperplasia may overproduce and secrete a novel, biologically active form of PTH with an intact 1-6 region but a presumably modified 12-18 region required for the detection in second-generation PTH assays.

Cinacalcet Hydrochloride (Sensipar) in Hemodialysis Patients on Active Vitamin D Derivatives with Controlled PTH and Elevated Calcium × Phosphate

Active vitamin D derivatives attenuate the severity of secondary hyperparathyroidism but often increase serum calcium (Ca) and phosphorus (P) as a result of enhanced intestinal absorption. The calcimimetic cinacalcet HCl lowers parathyroid hormone (PTH) and tends to decrease Ca x P. A 16-wk, open-label clinical trial was conducted in adult hemodialysis patients who had controlled PTH (biointact PTH [biPTH] 80 to 160 pg/ml) and elevated Ca x P (> 55 mg2/dl2) and were receiving paricalcitol > 6 microg/wk (or an equipotent dose of an alternative active vitamin D derivative). At the start of the study, active vitamin D derivatives were decreased to a mean equivalent dose of paricalcitol 6 microg/wk, and cinacalcet was titrated from 30 mg/d to a maximum possible dose of 180 mg/d. Of the 72 study patients, 53 (74%) completed 8 wk of dose titration with cinacalcet. In response to cinacalcet, the following mean percentage changes were observed: biPTH, -1.8%; Ca, -9.7% (P < 0.0001), phosphorus, -11.1% (P < 0.0001), and Ca x P, -20.1% (P < 0.0001). At the end of the study, approximate Kidney Disease Outcomes Quality Initiative targets for biPTH (< or = 160 pg/ml) were achieved in 85% (45 of 53) of patients and for Ca x P (< or = 55 mg2/dl2) in 72% (38 of 53) of patients. Concurrent achievement of both targets occurred in 47% (25 of 53) of patients. In this open-label clinical trial, hemodialysis patients who had controlled PTH but elevated Ca x P and were taking moderate- to high-dose active vitamin D derivatives achieved improved control of mineral metabolism with a combination of low-dose active vitamin D derivatives and cinacalcet. The long-term effects of this treatment regimen on clinical outcomes should be tested prospectively.