Circadian variation of mineral and bone parameters in end-stage renal disease.

BACKGROUND: Mineral and bone parameters are actively managed in end-stage renal disease (ESRD). However, whether these undergo circadian variation is not known. We investigated the circadian variation of mineral and bone parameters in patients on long-term hemodialysis. METHODS: Seventeen ESRD patients on long-term hemodialysis and eight volunteers without kidney disease were enrolled. Subjects had all medications that affect calcium-phosphate-parathyroid hormone balance (phosphate binders, vitamin D analogues, and calcimimetics) discontinued. Thereafter, for a period of 5 days, subjects consumed a diet controlled in calcium (1,200 mg per day) and phosphorus (1,000 mg per day) content. On the sixth day (a non-dialysis day for the ESRD patients), enrollees underwent twelve 2-h blood draws for phosphate, ionized calcium, parathyroid hormone (PTH), total 25-hydroxy vitamin D (25OHD), and fibroblast growth factor-23 (FGF-23). RESULTS: In the ESRD patients plasma phosphate demonstrated significant circadian variation (P < 0.00001). The peak occurred around 3:30 am and nadir occurred around 11:00 am. Ionized calcium (P = 0.0036), PTH (P = 0.0004) and 25OHD (P = 0.009) also varied significantly during the circadian period; for ionized calcium peak and nadir occurred around 12:15 pm and 8:00 pm, parathyroid hormone 5:45 pm and 10:15 am, and 25OHD 9:45 am and 4:00 pm respectively. FGF-23 did not show a significant circadian variation. Only phosphate (P < 0.0001) and PTH (P = 0.00008) demonstrated circadian variation in the control group. CONCLUSIONS: Blood concentrations of phosphate, calcium, PTH and 25-hydroxy vitamin D, exhibit a circadian variation in patients with ESRD. Knowledge of these phenomena is pertinent for the interpretation of clinical testing.

Bone mineral density and serum biochemical predictors of bone loss in patients with CKD on dialysis.

BACKGROUND AND OBJECTIVES: Use of bone mineral density (BMD) by dual-energy x-ray absorptiometry (DXA) is controversial for diagnosing bone loss in CKD patients on dialysis. The alternative quantitative computed tomography (QCT) is expensive and requires high radiation exposure. This study compared the two techniques and evaluated serum biochemical parameters for prediction of bone loss. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This prospective study enrolled patients from dialysis centers throughout Kentucky. BMD of the spine and hip was measured at baseline and after 1 year by DXA and QCT. Customary and novel serum biochemical parameters were obtained at the same times, including calcium, phosphorus, whole and intact parathyroid hormone, bone-specific alkaline phosphatase, procollagen type 1 N-terminal propeptide, tartrate-resistant acid phosphatase-5b, Dickkopf-1, fibroblast growth factor, and sclerostin. Rates of detection of osteoporosis by DXA and QCT were compared. Correlations were calculated between baseline biochemical parameters and BMD at baseline and changes over 1 year. Multivariable regression was performed to adjust for age, sex, body mass index, and race. RESULTS: Eighty-one patients completed the study (mean age=52.6 ± 12.3 years, 56% men, 53% African American, and median dialysis vintage=41 months). At baseline, QCT and DXA of the spine identified similar rates of osteoporosis (13.6% and 13.6%), but at the hip, DXA identified more osteoporosis (22.2% versus 13.6%). At any site and by either method, 33.3% of the patients were osteoporotic. Baseline BMD correlated with sclerostin, intact parathyroid hormone, bone-specific alkaline phosphatase, tartrate-resistant acid phosphatase-5b, and fibroblast growth factor. At 1 year, hip QCT identified a higher number of patients experiencing bone loss (51.3%) than DXA (38.5%). After multivariable adjustment, baseline sclerostin and tartrate-resistant acid phosphatase-5b predicted bone loss measured by QCT of the hip; procollagen type 1 N-terminal propeptide predicted cortical spine bone gain by QCT. CONCLUSIONS: QCT identified prospectively more bone loss at the hip than DXA. The baseline serum biochemical parameters sclerostin and tartrate-resistant acid phosphatase-5b were noninvasive independent predictors of bone loss in CKD patients on dialysis.

Influence of Secondary Hyperparathyroidism Induced by Low Dietary Calcium, Vitamin D Deficiency, and Renal Failure on Circulating Rat PTH Molecular Forms.

Rats(r) with secondary hyperparathyroidism were studied to define the relationship between vitamin D metabolites and rPTH levels measured by 3 different rat ELISAs. Controls and renal failure (RF) rats were on a normal diet, while 2 groups on a low-calcium (-Ca) or a vitamin D-deficient (-D) diet. RF was induced surgically. Mild RF rats had normal calcium and 25(OH)D but reduced 1,25(OH)(2)D levels (P < .001) with a 2.5-fold increased in rPTH (P < .001). Severe RF rats and those on a -Ca or -D diet had reduced calcium (P < .01) and 25(OH)D levels (P < .05), with rPTH increased by 2 (-Ca diet; P < .05), 4 (-D diet; P < .001), and 20-folds (RF; P < .001) while 1,25(OH)(2)D was high (-Ca diet: P < .001) or low (-D diet, RF: P < .001). 25(OH)D and 1,25(OH)(2)D were positively and negatively related on the -Ca and -D diets, respectively. rPTH molecular forms behaved as expected in RF and on -Ca diet, but not on -D diet with more C-rPTH fragments when less were expected. This may be related to the short-time course of this study compared to prior studies.

Nontruncated amino-terminal parathyroid hormone overproduction in two patients with parathyroid carcinoma: a possible link to HRPT2 gene inactivation.

OBJECTIVE: Some patients with parathyroid carcinoma present with an over-production of nontruncated amino-terminal (NT-N) parathyroid hormone (PTH), a post-transcriptionally modified form of PTH(1-84). This is usually picked up on an elevated whole (W) PTH (third-generation)/total (T) (second-generation) PTH assay ratio (N > 0·8). PATIENTS AND DESIGN: Two parathyroid cancer patients with several episodes of hypercalcaemia and multiple surgeries are described. In both patients, W-PTH, T-PTH and circulating PTH molecular forms separated by high-pressure liquid chromatography (HPLC) were measured with the same assays. qPCR was used to study HRPT2 gene mutation. RESULTS: The first patient had total calcium of 3·8 and 3·22 mmol/l before the fourth and fifth surgeries, and third/second-generation PTH ratios of 2·95 and 3·6, respectively. After the fourth surgery, the ratio remained normal for 1 year and increased progressively to 3·6 over 15 months. This preceded hypercalcaemia by 6 months. The ratio became normal after the fifth surgery. HPLC analysis disclosed an over-expression of NT-N PTH to 82·2% (N < 10%) relative to hPTH(1-84) before the fifth surgery. A deletion of all the tested exons of the HRPT2 gene was identified. In the second patient, W-PTH/T-PTH ratio was 0·89 when serum calcium was 3·3 mmol/l. NT-N PTH was also over-expressed at 51·9%. An inactivating mutation of the HRPT2 gene was also identified. CONCLUSIONS: This may suggest that a progressive rise in third/second-generation ratio may have possible clinical utility to monitor parathyroid cancer recurrence. A possible association between NT-N PTH overproduction and HRPT2 gene inactivation is also suggested.

Changes in bone mineral parameters, vitamin D metabolites, and PTH measurements with varying chronic kidney disease stages.

Vitamin D deficiency is associated with an increased risk of many diseases (skeletal and nonskeletal). Emerging data also associate high concentrations of serum parathyroid hormone (PTH) with morbidity and increased mortality in patients both with and without known chronic kidney disease (CKD). Understanding the relationship between vitamin D and PTH and the determinants of PTH is therefore important. We performed a cross-sectional study of 203 patients with varying stages of CKD randomly recruited from the Renal Unit database at our institution. Detailed case review was performed, and samples of fasting blood were taken for biochemical analyses. We measured standard biochemistry, 25-hydroxyvitamin D (25-OHD), 1,25-OHD, and three PTH measurements [1-84 PTH, total PTH, and derived N-terminal truncated, 7-84 PTH (cPTH)]. Vitamin D deficiency was high, with 86% of patients having 25-OHD levels below 30 ng/ml. Estimated glomerular filtration rate (eGFR) was not associated with 25-OHD levels, whereas 1,25-OHD was lower in those with CKD stage 5 versus stage 4, who were not treated with vitamin D metabolites (18 vs. 65 pg/ml, respectively; P < 0.05). All three PTH measurements increased with worsening eGFR, with this finding being more pronounced in those patients who were not treated with vitamin D metabolites. The slope of the regression line of cPTH on eGFR tended to be steeper, -0.90, compared to -0.81 for total PTH and -0.80 for 1-84 PTH (P = 0.06). The ratio of total PTH to cPTH did decrease significantly through the range of CKD stages (P = 0.03). The determinants of PTH were similar for all three PTH measurements, with eGFR having a strong inverse relationship, with weaker relationships for 25-OHD and ionized calcium on multivariate analyses. We confirm that there is a complex relationship between 25-OHD, eGFR, and PTH. Total PTH, 1-84 PTH, and cPTH increase with increasing CKD stages, with a relatively greater increase in cPTH, although the clinical significance of this finding remains uncertain. The three PTH measurements had similar correlations with the biochemical and clinical variables studied, suggesting that either total PTH or 1-84 PTH can be used in clinical practice when evaluating vitamin D and PTH status.

Rat parathyroid hormone (rPTH) ELISAs specific for regions (2-7), (22-34) and (40-60) of the rat PTH structure: influence of sex and age.

Rat (r) PTH ELISAs were used to study the influence of age and sex on rPTH levels and circulating PTH molecular forms separated by HPLC. Standard curves and saturation analysis were undertaken to define epitopes. Rats were sacrificed at approximately 27, 47 and 75days. Relevant biochemical parameters and 25(OH) vitamin D were measured. Differences between sexes were analyzed by Kruskal-Wallis ANOVA, followed by Dunn's test. Epitopes were localized in regions 2-7, 22-34 and 40-60 of rPTH structure for whole (W), total (T) and carboxyl (C) rPTH ELISAs. The W-rPTH assay only detected rPTH(1-84) and N-PTH in circulation while the T-PTH assay further detected large C-rPTH fragments. The C-rPTH assay detected all circulating rPTH molecular forms including smaller C-rPTH fragments. In both sexes, weight (p<0.001), ionized calcium, creatinine, albumin and 25(OH)D values (p<0.001) increased with age, while phosphate and alkaline phosphatase decreased (p<0.001). In male rats, W-rPTH remained unchanged, while T-rPTH rose slightly (p<0.05) and C-rPTH declined by half with time (p<0.001). In female rats, W-rPTH (p<0.05), T-rPTH (p<0.001) and C-rPTH (p<0.01) all increased in older animals. In both sexes, C-rPTH/W-rPTH and C-rPTH/T-rPTH ratios decreased between 25 and 47 days, to rise again between 47 and 75 days. The initial decrease may represent an adaptation to weaning and a change of diet between 25 and 47 days while the rise corresponds to higher calcium and 25(OH)D levels between 47 and 75 days. These changes were more pronounced in female rats, indicating an influence of sex on PTH molecular form secretion or metabolism.

Intact PTH combined with the PTH ratio for diagnosis of bone turnover in dialysis patients: a diagnostic test study.

BACKGROUND: Determination of parathyroid hormone (PTH) level is the most commonly used surrogate marker for bone turnover in patients with stage 5 chronic kidney disease on dialysis therapy (CKD-5D). The objective of this study is to evaluate the predictive value of various PTH measurements for identifying low or high bone turnover rate. STUDY DESIGN: Diagnostic test study. SETTINGS & PARTICIPANTS: 141 patients with CKD-5D from 15 US hemodialysis centers. INDEX TESTS: Intact PTH, PTH 1-84, and PTH ratio (ratio of level of PTH 1-84 to level of large carboxy-terminal PTH fragments). REFERENCE TEST OR OUTCOME: Bone turnover determined using bone histomorphometry. OTHER MEASUREMENTS: Demographic and treatment-related factors, serum calcium and phosphorus. RESULTS: Patients presented histologically with a broad range of bone turnover abnormalities. In white patients with CKD-5D (n = 70), PTH ratio <1.0 added to intact PTH level <420 pg/mL increased the positive predictive value for low bone turnover from 74% to 90%. In black patients (n = 71), adding PTH ratio <1.2 to intact PTH level <340 pg/mL increased the positive predictive value for low bone turnover from 48% to 90%. Adding PTH ratio >1.6 to intact PTH level of 340-790 pg/mL increased the positive predictive value for high bone turnover from 56% to 71%. LIMITATIONS: Because the research protocol called for carefully controlled blood specimen handling, blood drawing and routine specimen handling might be less stringent in clinical practice. By limiting study participation to black and white patients with CKD-5D, we cannot comment on the roles of intact PTH, PTH 1-84, and PTH ratio in other racial/ethnic groups. CONCLUSION: In black patients with CKD-5D, the addition of PTH ratio to intact PTH measurements is helpful for diagnosing low and high bone turnover. In white patients with CKD-5D, it aids in the diagnosis of low bone turnover.

Intraoperative parathyroid hormone levels measured by intact and whole parathyroid hormone assays in patients with Graves' disease.

PURPOSE: To find out if the whole parathyroid hormone (wPTH) assay has practical advantages over the intact (iPTH) assay in patients with Graves' disease. METHODS: We measured iPTH and wPTH levels before and after subtotal thyroidectomy in 111 consecutive patients (94 women and 17 men) with Graves' disease. Blood samples for assays were obtained after the induction of anesthesia (basal) and following skin closure (postoperative). RESULTS: There was a significant correlation between wPTH and iPTH in both the basal and postoperative levels. Logistic regression analyses examining the relationship between the reduction in parathyroid hormone (PTH) levels and the incidence of tetany revealed that both the wPTH and iPTH assays were significantly equally predictive of postoperative tetany. CONCLUSION: We found that both the wPTH and iPTH assays were useful for predicting postoperative tetany in patients with Graves' disease, yielding similar results.

Third-generation parathyroid hormone assays and all-cause mortality in incident dialysis patients: the CHOICE study.

BACKGROUND: There has been controversy about the utility of new third-generation parathyroid hormone (PTH) assays measuring only 1-84 PTH, with few large studies comparing second- and third-generation PTH measurements in patients with ESRD. METHODS: We measured 1-84 PTH ('biointact' or 'whole' PTH) and total PTH ('intact' PTH) in a national cohort of 515 incident dialysis patients from banked frozen EDTA plasma (median follow-up, 35 months) and examined the accuracy of estimating 1-84 PTH from total PTH and the associations of these levels with patient characteristics and mortality. RESULTS: The 1-84 PTH and total PTH levels were closely correlated. Higher 1-84 PTH was associated with African-American race and higher serum phosphate and lower calcium levels. The percentage of total PTH represented by 1-84 PTH was, on average, 53%, but with a wide range (25-89%). Calculating 1-84 PTH from total PTH using a proposed standard conversion factor (54%) led to misclassification of 8% of the population compared with measured 1-84 PTH. In a multivariate Cox proportional hazards model for all-cause mortality, a 1-84 PTH value >160 pg/ml was associated with increased risk of mortality (HR = 1.62, 95% CI, 1.03-2.54) compared to a level of 80-160 pg/ml. Elevated total PTH, 7-84 PTH and the 1-84 PTH/7-84 PTH ratio were not significantly associated with mortality. CONCLUSIONS: The 1-84 PTH and total PTH are highly correlated. Elevated 1-84 PTH was significantly associated with increased mortality, whereas total PTH did not reach statistical significance. Thus, although in other respect they are similar, there may be utility in measuring 1-84 PTH for its associations with mortality.

An N-terminal molecular form of parathyroid hormone (PTH) distinct from hPTH(1 84) is overproduced in parathyroid carcinoma.

BACKGROUND: A new parathyroid hormone (PTH) species, the N-terminal PTH form (N-PTH), is distinct from intact human PTH of 84 amino acid residues [hPTH(1-84)] and is recognized in a 3rd-generation assay of "whole" PTH (wPTH; the 1-2 epitope) but not in a 2nd-generation assay of "total" PTH (tPTH; the 12-18 epitope). N-PTH usually represents <15% of wPTH but can be overproduced in severe primary hyperparathyroidism (PHPT) and secondary hyperparathyroidism. We investigated whether N-PTH is also overproduced in parathyroid cancer and whether N-PTH concentration is influenced by calcimimetic therapy. METHODS: We studied 8 patients with parathyroid carcinoma before and at week 16 of cinacalcet therapy, 6 patients with PHPT, and 6 control individuals. We fractionated sera with HPLC and analyzed fractions with the 2 assays to quantify hPTH(1-84), N-PTH, and non-(1-84) PTH fragments. RESULTS: Half of parathyroid carcinoma patients had an increased wPTH:tPTH ratio [mean (SD), 1.35 (0.29)]; the others had a typical ratio [0.72 (0.12)]. HPLC fractionation of sera from 2 high-ratio patients confirmed N-PTH overproduction [65% (12%) of wPTH]. The N-PTH fraction was <15% of wPTH in PHPT and healthy individuals. Calcimimetic therapy appreciably reduced calcium concentrations in parathyroid carcinoma patients but had little influence on PTH concentration, the wPTH:tPTH ratio, or the PTH HPLC profile. CONCLUSION: N-PTH is overproduced in some parathyroid cancer patients, but calcimimetic therapy does not influence its production. The clinical implications of this finding in parathyroid carcinoma await additional studies with an emphasis on N-PTH's biological activity and with larger numbers of patients.

Lack of comparability of intact parathyroid hormone measurements among commercial assays for end-stage renal disease patients: implication for treatment decisions.

BACKGROUND: Variability among assays used to measure intact parathyroid hormone (iPTH) is of particular concern because of the routine use of iPTH assay results to guide management of osteodystrophy and calcium metabolism in patients with end-stage renal disease (ESRD). The aim of this study was to determine the extent to which results from commercially available iPTH assays diverge from results obtained with the Nichols Allegro(R) Intact PTH immunoradiometric assay (IRMA), which was used as evidence in the development of the National Kidney Foundation's Kidney Disease Outcomes Quality Initiative Clinical Practice Guidelines. METHODS: We divided EDTA plasma from 46 dialysis patients with ESRD and measured iPTH values with the following commercially available iPTH assays: Nichols' Allegro iPTH IRMA, Nichols Advantage iPTH immunochemiluminescent assay (ICMA), Scantibodies' Total Intact PTH IRMA, DiaSorin's N-tact iPTH IRMA, DPC's Coat-A-Count iPTH IRMA, Roche's Elecsys iPTH ICMA, and DSL's Active iPTH IRMA. RESULTS: Method comparison showed considerable interassay differences in the measurement of iPTH in ESRD patients. IPTH values assessed by other methods ranged, on average, from 60% to 152% of the Nichols Allegro IRMA values. Of the 6 iPTH assays tested, only the Scantibodies Total Intact PT IRMA (P = 0.7554) and the Roche Elecsys iPTH ICMA (P = 0.1327) resulted in iPTH values not statistically different from those obtained with the Nichols Allegro iPTH IRMA. CONCLUSIONS: Noncomparability among iPTH assays remains a distinct problem for the management of ESRD patients. These results should be taken into consideration when determining the course of medical treatment based on measured iPTH concentrations.

Acute regulation of circulating parathyroid hormone (PTH) molecular forms by calcium: utility of PTH fragments/PTH(1-84) ratios derived from three generations of PTH assays.

CONTEXT: The quantitative evaluation of circulating PTH peaks revealed by PTH assays after HPLC separation constitutes the best way to study the behavior of PTH molecular forms, but it is also impractical. OBJECTIVE: The objective of the study was to investigate the regulation of circulating PTH molecular forms by calcium through the use of PTH fragments/PTH (1-84) ratios derived from PTH assays with different specificities before and after HPLC separation of circulating PTH. DESIGN: CaCl2 and Na citrate were infused in eight volunteers. PTH was measured in serum and HPLC fractions at different calcium concentrations in PTH assays reacting with regions 1-2 (CA), 12-18 (T), and 65-69 (C) of the PTH structure. RESULTS: From hypo- to hypercalcemia, the C/CA ratio had the highest range (1.92 to 9.75; P < 0.001), and the C/T ratio had a higher range (1.69 to 6.11; P < 0.01) than the T/CA ratio (1.15 to 1.86). Human (h) PTH (1-84) represented 32.7 and 4.3% of circulating PTH in hypo- and hypercalcemic HPLC profiles, respectively. These numbers were 5 and 0.9% for amino-terminal (N)-PTH, an amino-terminal form of PTH distinct from hPTH (1-84), 7.3 and 6.8% for non-(1-84) PTH or large C-PTH fragments with a partially preserved N structure, and 54.9 and 88.1% for C-PTH fragments missing a N structure. The HPLC C-PTH fragments to hPTH (1-84) ratio had the most extensive range (1.67 to 20.58). Despite their quantitative differences, all ratios identified identical behavior of PTH fragments relative to PTH (1-84). CONCLUSIONS: PTH assay ratios are an adequate tool to investigate the modulation of PTH molecular forms, even if all PTH assays show some undesirable cross-reactivity with certain circulating forms of PTH.

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.

Parathyroid hormone assay drift: an unappreciated problem in dialysis patient management.

The Kidney Disease Outcomes Quality Initiative (K/DOQI) bone metabolism guidelines assume that clinicians use the Nichols intact parathyroid hormone immunoradiometric assay (iPTH IRMA) upon which K/DOQI was based. But for more than a decade, virtually all PTH assay results used for routine end-stage renal disease (ESRD) clinical management have not been generated with this test. Results from the most widely used PTH assays for ESRD patient testing in the United States have varied from 1999 to 2005. The Nichols chemiluminescent Advantage iPTH assay results shifted upwards significantly in 1999 and remained elevated until 2005. From 2003 to 2005, results from the Nichols Advantage Bio-Intact PTH assay shifted upward on average by 29% to 52%. These changes in the most widely used PTH assays have made use of the K/DOQI guidelines with these assays both inappropriate and potentially harmful to patients.

Overproduction of an amino-terminal form of PTH distinct from human PTH(1-84) in a case of severe primary hyperparathyroidism: influence of medical treatment and surgery.

OBJECTIVE: Rare patients with severe primary hyperparathyroidism present with large parathyroid tumours, severe hypercalcaemia, very high PTH levels and osteitis fibrosa cystica. Some of these patients display a large amount of C-PTH fragments in circulation and present with a higher C-PTH/I-PTH ratio than seen in less severe cases of primary hyperparathyroidism. We wanted to determine how PTH levels and circulating PTH high-performance liquid chromatography (HPLC) profiles analysed with PTH assays having different epitopes could be affected by medical and surgical treatment in such patients. DESIGN: A 55-year-old man with severe hypercalcaemia (Ca(2+): 2.01 mmol/l), very high PTH levels (CA-PTH 82.1 and T-PTH 72 pmol/l) caused by a large parathyroid tumour (7.35 g) and accompanied by significant bone involvement (alkaline phosphatase of 185 UI/l and subperiostal bone resorption of hands) was referred to us. Blood was obtained at various time points during his medical treatment, before and after surgery, to measure parameters of calcium and phosphorus metabolism, and of bone turnover. HPLC separations of circulating PTH molecular forms were performed and analysed with PTH assays having 1-4 (CA), 12-18 (T), 26-32 (E) and 65-84 (C) epitopes. RESULTS: Before surgery, serum Ca2+ was nearly normalized with hydratation, intravenous (IV) pamidronate and oral vitamin D administration. Despite a decrease in Ca2+ to 1.31 mmol/l, CA-PTH and T-PTH levels decreased by half in relation to a threefold increase in basal 1,25-dihydroxyvitamin D [1,25(OH)2D] level (94 to 337 pmol/l). After this initial positive response, hypercalcaemia and elevated CA- and T-PTH levels recurred even if 1,25(OH)2D levels remained elevated. The tumour was removed surgically and proved to be poorly differentiated with nuclear atypia and mitosis. After surgery, the Ca2+ level and PTH secretion normalized. The higher CA-PTH level relative to the T-PTH level observed before surgery in this patient was related to the oversecretion of an amino-terminal (N) form of PTH recognized by PTH assays with (1-4) or (26-32) epitopes but not by the T-PTH assay with a (12-18) epitope. This molecular form represented 50% of CA-PTH measured in this patient, but only 7% in less severe cases of primary hyperparathyroidism. It was unaffected by medical therapy and disappeared after surgery. CONCLUSION: The relationship between the overexpression of this N-PTH molecular form and severe primary hyperparathyroidism remains unclear. Further studies will be required in these rare patients to see whether N-PTH is a marker of less well differentiated parathyroid tumours and/or relates to the overproduction of C-PTH fragments in the presence of severe hypercalcaemia.

Parathyroid hormone and growth in children with chronic renal failure.

BACKGROUND: In pediatric chronic renal failure (CRF) optimal parathyroid hormone (PTH) concentrations that minimize renal osteodystrophy and maximize growth are unknown. The search for optimum concentrations has been complicated as currently used "intact" PTH (iPTH) assays cross-react with long carboxyl-terminal PTH fragments (C-PTH), which antagonize the biologic actions of 1-84 PTH. The purpose of this study was to investigate the relationship between PTH, the 1-84 PTH:C-PTH ratio and growth rate in children with CRF. METHODS: A total of 162 patients, median (range) age 9.9 years (0.3 to 17.1 years), were recruited: 136 with a glomerular filtration rate (GFR) <60 mL/min/1.73 m(2)[96 managed conservatively (CRF group) and 40 transplanted patients], and 26 dialysis patients. Over a median (range) period of 1.1 years (0.5 to 1.7 years), children attended five (three to 15) clinics at which iPTH, cyclase-activating PTH (CAP-PTH), and height were measured. RESULTS: Mean PTH concentrations were within the normal range for both assays for the CRF group and up to twice the upper limit of normal for the dialysis group; CAP-PTH 24.8 pg/mL and 59.9 pg/mL (normal range 5 to 39 pg/mL), iPTH 37.1 pg/mL, and 102.6 pg/mL, respectively (normal range 14 to 66 pg/mL). The patients grew normally (change in height standard deviation score per year (DeltaHtSDS) =-0.01). There was no relationship between PTH concentrations and DeltaHtSDS in any patient group. The 1-84 PTH:C-PTH ratio was lower in dialyzed patients (P= 0.003), with worsening renal function (P= 0.047) and with PTH concentrations outside the normal range (P= 0.01). There was a weak correlation between the 1-84 PTH:C-PTH ratio and the DeltaHtSDS (r= 0.2, P= 0.01). CONCLUSION: Normal range PTH concentrations are appropriate, allowing normal growth in children with CRF managed conservatively. C-PTH may be of clinical significance.

Differences between "intact" PTH and 1-84 PTH assays in chronic renal failure and dialysis.

"Intact" parathyroid hormone (iPTH) assays overestimate actual PTH as they cross-react with non (1-84) PTH fragments (C-PTH) that accumulate in renal failure. New assays that measure just 1-84 PTH (CAP-PTH) are now available. It has been suggested that there is a linear relationship between the two assays; however, increased C-PTH levels are found as glomerular filtration rate (GFR) declines and in patients on dialysis. We investigated the relationship between iPTH and CAP-PTH in children with chronic renal failure (CRF) managed conservatively and on dialysis. We investigated 241 children, 156 with a GFR <60 ml/min per 1.73 m(2) managed conservatively, 49 post renal transplant (and GFR <60 ml/min per 1.73 m(2)) and 36 on dialysis, by measuring PTH levels by iPTH and CAP-PTH assays. Multiple regression analysis comparing differences between PTH levels in each patient group was performed. Correlation slopes between iPTH and CAP-PTH assays differed between CRF and dialysis patients (P=0.001). These assays perform differently in CRF and dialysis patient groups. Studies investigating the correlation between newer assays and bone histology are required to determine whether these more-specific PTH assays are superior surrogate markers of bone turnover.

Sequential changes in plasma intact and whole parathyroid hormone levels during parathyroidectomy for secondary hyperparathyroidism.

Most commercial assays for intact parathyroid hormone (iPTH) cross-react with non-PTH1-84 fragments (likely to be PTH7-84). We aimed to evaluate a whole PTH assay that measured only PTH1-84 by comparing it with an assay measuring iPTH levels during parathyroidectomy in secondary hyperparathyroidism (HPT). Twenty-eight patients with secondary HPT who underwent total parathyroidectomy with autotransplantation served as subjects. Blood samples for postoperative assay were drawn after anesthesia; immediately prior to excision of the last parathyroid gland; and at 5, 10, and 15 minutes after excision. The PTH7-84 level was calculated by subtracting the whole PTH value from the iPTH value. Plasma whole PTH decreased more rapidly than iPTH after parathyroidectomy (p < 0.0001). PTH levels that decreased by 50% or more from levels prior to excision to 10 minutes after excision were used to predict successful parathyroidectomy; decreases in whole PTH substantiated curative surgery for all patients without introducing false-positive and false-negative results. iPTH levels decreased by at least 50% in only 16 patients at 10 minutes after excision without false-positive results. Out of 11 cases in which iPTH decreased less than 50%, two were true-negatives and nine were false-negatives. Decreases in whole PTH levels more accurately reflect surgical outcome than do decreases in iPTH levels during parathyroidectomy in secondary HPT patients. Even though the quick iPTH assay is used infrequently during surgery for secondary HPT, our results suggest that a quick whole PTH assay may be more useful than the iPTH assay currently used in parathyroidectomy procedures for secondary HPT.

Evidence that the amino-terminal composition of non-(1-84) parathyroid hormone fragments starts before position 19.

BACKGROUND: Non-(1-84) parathyroid hormone (PTH) fragments are large C-terminal fragments of PTH with a partially preserved N-terminal structure. They differ from other C-terminal PTH fragments, which do not have an N-terminal structure and do not react in intact PTH assays. We aimed to identify the minimal N-terminal structure common to all non-(1-84) PTH fragments. METHODS: Sera obtained from six healthy individuals and six patients with primary hyperparathyroidism, and six serum pools from dialysis patients with different PTH concentrations were fractionated by HPLC and analyzed by four different PTH assays. Each assay was characterized by saturation analysis of its detection antibody and capacity to react with different PTH fragments. Human PTH(1-84) [hPTH(1-84)] calibrators were normalized to an in-house hPTH(1-84) calibrator. RESULTS: The cyclase-activating PTH (CA-PTH) assay had an early (1, 2,) epitope and reacted only with hPTH(1-84). The other assays had epitopes in region (13-34). Total and intact PTH assays had epitopes proximal to position 18 and reacted equally well with hPTH(1-84) and hPTH(7-84), and the Elecsys PTH assay had an epitope distal to position 19, being saturable by hPTH(18-48) and also reacting with [Tyr(34)]hPTH(19-84). The HPLC profiles obtained with these assays showed that non-(1-84) PTH fragments did not react in the CA-PTH assay, as expected. The amount of non-(1-84) PTH detected by the other three assays was similar when the assay results were normalized to a common calibrator. CONCLUSIONS: The results suggest that the amount of non-(1-84) PTH detected by epitopes proximal or distal to position 19 of the PTH structure is identical, indicating a common minimum structure starting before position 19. This in turn points to a probable high-affinity interaction with the C-PTH receptor, as observed previously with [Tyr(34)]hPTH(19-84) in various cell lines and in mouse osteocytes with PTH/PTHrP type I receptor ablation.