Highly sensitive two-site immunoradiometric assay of parathyrin, and its clinical utility in evaluating patients with hypercalcemia

We have developed a highly sensitive, two-site immunoradiometric assay (IRMA) for human parathyrin (PTH) that is specific for the intact, secreted, biologically active 84-amino-acid peptide. This assay has several technical advantages: it does not detect even high concentrations of inactive carboxyl-terminal fragments, results are available within 24 h, and the detection limit for intact hormone is low (1 ng/L). The assay readily measures concentrations of PTH in all healthy subjects and distinguishes these values from low or undetectable PTH values observed in clinical situations in which PTH secretion is expected to be suppressed. We found complete separation of results from 37 patients with surgically proven hyperparathyroidism and those from 23 patients with hypercalcemia associated with malignancy, the latter having PTH values at or below the lower limits of normal for this assay. The sensitivity, specificity, and rapid turnaround time of this two-site IRMA should advance the laboratory evaluation of patients with disorders of calcium metabolism.     

Intact parathyrin in postmenopausal women

To establish a reference range, we measured intact parathyrin (parathyroid hormone, PTH) in 245 healthy postmenopausal women, ages 42-75 years, with use of the Allegro Intact PTH Kit from Nichols Institute Diagnostics. We also assayed serum from a subset of 120 of the women with kits specific for mid-molecule PTH. The mean intact PTH concentration for the 245 women was 32 ng/L (95% confidence interval 14-60 ng/L). Intact PTH values in these subjects were not normally distributed, although calcium concentrations in the same samples were. There was positive, but not significant (r = 0.12, P = 0.06), correlation between intact PTH and age, and a significant negative correlation between serum calcium and intact PTH that was not observed between calcium and mid-molecule PTH. The improved sensitivity of the intact PTH assay makes it useful in studies of calcium homeostasis in the normal population.     

Immunoradiometric assay of parathyrin with polyclonal and monoclonal region-specific antibodies.

In this immunoradiometric assay (IRMA) of parathyrin (PTH) a polyclonal anti-amino-PTH(1-34) is the capture antibody and a radiolabeled monoclonal anti-hPTH(44-68) is the second antibody. Gel filtration of serum from a hyperparathyroid patient yielded only a single peak of PTH, corresponding to the elution position of synthetic PTH(1-84). Healthy elderly individuals (ages 78 +/- 5 y, mean +/- SD, n = 45) had PTH concentrations (21 +/- 13 ng/L) not significantly higher than those from healthy younger (38 +/- 11 y) adults (20 +/- 8 ng/L, n = 94). Assay results agreed well with those obtained with a carboxyl-terminal PTH assay both in normal subjects (r = 0.63, P less than 0.001) and in patients with primary hyperparathyroidism (r = 0.59, P less than 0.001). Both assays equally discriminated patients with surgically confirmed primary hyperparathyroidism from normal individuals, but the PTH(1-84) IRMA also allowed a nearly absolute discrimination between normal subjects and patients with primary hypoparathyroidism (undetectable serum PTH in 18 of 21 cases) and secondary hypoparathyroidism (caused by hypercalcemia that was caused by a malignant tumor, PTH 1.3 +/- 1.3 ng/L, n = 32). Moreover, the PTH(1-84) IRMA is more sensitive (detection limit in serum, 0.8 ng/L) and easier and quicker to perform than the carboxyl-terminal assay.     

Technical and clinical characterization of the Bio-PTH (1-84) immunochemiluminometric assay and comparison with a second-generation assay for parathyroid hormone

BACKGROUND: The Bio-Intact parathyroid hormone (1-84) assay (Bio-PTH), a newly developed two-site immunochemiluminometric assay, measures exclusively PTH (1-84) in contrast to second-generation "intact PTH" (I-PTH) assays. We investigated the technical performance and clinical significance of this new assay. METHODS: PTH was measured simultaneously by the Bio-PTH assay and Allegro intact PTH IRMA in sera from Japanese patients with calcium disorders. RESULTS: Measured Bio-PTH in serum was unaffected by six freeze-thaw cycles and was stable at 4 degrees C for 7 days and during storage at -20 or -80 degrees C over 28 days. The calibration curve was linear to 1800 ng/L. The detection limit was 3.9 ng/L. The intra- and interassay imprecision was <2.8% and 3.5%, respectively, for analyte concentrations spanning the range of the calibration curve. Bio-PTH was unaffected by a 1000-fold excess of PTH (7-84), although I-PTH reacted equally with PTH (7-84) and PTH (1-84). Bio-PTH was correlated with I-PTH in healthy individuals (r = 0.953; P <0.0001; n = 26) and in the full population without renal dysfunction (r = 0.994; P <0.0001; n = 62). In 72 volunteers, mean (SD) Bio-PTH was 22.2 (7.1) ng/L, or 62% of the mean I-PTH [36.1 (22.3) ng/L]. This ratio was 51% in hemodialysis patients (n = 177). Mean Bio-PTH was high in patients with primary hyperparathyroidism [121 (85) ng/L; n = 18] and hemodialysis patients [102 (104) ng/L; n = 177], low in idiopathic hypoparathyroidism [5.5 (2.8) ng/L; n = 4], and within 2 SD of the mean for healthy controls in Paget disease of the bone [34 (15) ng/L; n = 9] and bone metastasis [24 (12) ng/L; n = 8]. CONCLUSION: The Bio-PTH assay is sensitive and precise and produces expected results for patients with the studied disorders of calcium metabolism.     

Performance and diagnostic application of a two-site immunoradiometric assay for parathyrin in serum

The "N-tact" immunoradiometric assay (IRMA) from INCSTAR for parathyrin (PTH) in serum involves a 125I-labeled affinity-purified antiserum to PTH 1-34 and an affinity-purified antiserum to PTH 39-84, the latter bound to a polystyrene bead. The mean detection limit, determined in six consecutive assays, was 4 ng/L. The within-batch CV was less than 7% in the range 15 to 2135 ng/L. The between-batch CV was 11.7% and 5.3% at 30 and 371 ng/L, respectively. Serum PTH in 14 proven cases of primary hyperparathyroidism was 49-808 (median 111) ng/L, undetectable (less than 5 ng/L) in 10 cases of primary hypoparathyroidism and in 10 cases of hypercalcemia associated with malignancy, compared with 7-39 ng/L in 45 normal subjects. PTH was 9 to 19 ng/L in four patients with familial benign hypercalcemia. In 39 patients with renal failure, apparent concentrations were 14 to 857 (median 133) ng/L, but sera from these patients pre-diluted with zero standard did not parallel dilutions of the standard, PTH 1-84. PTH concentrations were not significantly decreased in blood or serum kept at 20 degrees C for up to 6 h. After successful removal of a parathyroid adenoma, the mean half-time for disappearance of PTH in vivo in five hyperparathyroid patients was 3.3 min.     

Assay-specific decision limits for two new automated parathyroid hormone and 25-hydroxyvitamin D assays

BACKGROUND: The recent development of nonradioactive automated assays for serum parathyroid hormone (PTH) and 25-hydroxyvitamin D (25OHD) has made measurement of these two hormones possible in many laboratories. In this study, we compared two new assays for PTH and 25OHD adapted on an automated analyzer, the LIAISON, with two manual immunoassays used worldwide. METHODS: We studied 228 osteoporotic patients, 927 healthy individuals, 38 patients with primary hyperparathyroidism, and 167 hemodialyzed patients. Serum PTH was measured with the Allegro and the LIAISON assays, and 25OHD was measured with DiaSorin RIA and the LIAISON assay. Regression analysis was used to calculate decision thresholds for the LIAISON assays that were equivalent to those of the Allegro PTH and DiaSorin 25OHD assays. RESULTS: The 25OHD concentrations obtained with the LIAISON assay and the RIA in osteoporotic patients were well correlated (r = 0.83; P <0.001). Regression and Bland-Altman analyses suggested that the LIAISON 25OHD assay reads lower than the DiaSorin RIA at low concentrations but higher at high concentrations. However, the cutoff (50 nmol/L) used in our laboratories to define vitamin D insufficiency with the DiaSorin RIA is applicable to the LIAISON 25OHD assay. In 927 healthy individuals, the 3rd-97th percentile intervals were 3-80 ng/L and 13-151 nmol/L for the LIAISON PTH and 25OHD concentrations, respectively. However, 506 individuals (54.6%) were vitamin D-insufficient; we therefore considered only the 421 individuals with a LIAISON 25OHD >50 nmol/L as eligible for the reference population for the LIAISON PTH assay. In this group, the 3rd-97th percentile interval for LIAISON PTH was 3-51 ng/L. Considering upper reference limits of 46 and 51 ng/L for the Allegro and LIAISON assays, respectively, the frequency of above-normal PTH concentrations in patients with primary hyperparathyroidism was similar in both assays. Regression analysis between serum PTH measured by the Allegro and LIAISON assays in 167 hemodialyzed patients and the corresponding Bland-Altman analysis of these data suggest that the LIAISON PTH assay tends to read higher than the Allegro assay at low concentrations but lower at high concentrations (>300 ng/L). CONCLUSIONS: Because clinical decision limits for both PTH and 25OHD should be assay specific, we propose equivalences between these assays and two manual assays used worldwide. These assay-specific decision limits should help potential users of the LIAISON PTH and 25OHD assays.     

Immunochemiluminometric and immunoradiometric determinations of intact and total immunoreactive parathyrin: performance in the differential diagnosis of hypercalcemia and hypoparathyroidism

Parathyrin (parathyroid hormone; PTH) was measured with three immunoassays: a two-site immunochemiluminometric (ICMA) and a two-site immunoradiometric (IRMA) method for intact PTH, and a sensitive radioimmunoassay for mid-region or "total" PTH, measuring both intact hormone and inactive fragments. Single specimens from normal subjects and from individuals with primary hyperparathyroidism, hypercalcemia associated with malignancy, and hypoparathyroidism were analyzed with all three methods. All individuals with primary hyperparathyroidism showed absolutely above-normal concentrations with the mid-region RIA, 28 of 29 did with the ICMA, and 21 of 29 did with the IRMA. PTH concentrations in primary hyperparathyroidism were most increased relative to normal subjects with the mid-region assay (10.4 times), less so with the intact assays (ICMA 5.5 times; IRMA 5.3 times). Concentrations of intact PTH were suppressed below normal in nearly all patients with hypercalcemia associated with malignancy, as measured with the ICMA (26 of 30) and the IRMA (28 of 30) assays. In marked contrast, results for mid-region PTH were normal or slightly above normal, consistent with studies suggesting that the parathyroids secrete both intact hormone and inactive fragments, the former being more sensitive to suppression by hypercalcemia. In hypoparathyroidism PTH concentrations were detectable but below normal in all patients by the intact assays and in all but one patient by the mid-region assay. These low concentrations are probably due to a nonspecific serum effect that could be resolved with selection of a more appropriate standard matrix. Although all three assays are useful in the differential diagnosis of hypercalcemia, two-site intact assays are more convenient and more specific in patients with compromised renal function.     

Evaluation of a chemiluminescence immunoassay for the determination of intact parathyroid hormone using the ADVIA Centaur

We tested a new chemiluminescence immunoassay for intact parathyroid hormone (PTH) (ADVIA Centaur intact PTH-serum assay). It is a two-site sandwich immunoassay using direct chemiluminescence technology. We investigated precision with serum pools at three levels of the analyte, analyzed in duplicate for 12 days. Total coefficients of variation (CVs) were between 4.6 and 14.4%. The intra-assay precision was between 4.4 and 6.1%. Day-to-day reproducibility was between 1.5 and 13.1% for pools with a PTH concentration between 10 pg/ml and 70 pg/ml (about 1 to 7 pmol/l). The analytical sensitivity was 3.1 pg/ml. The functional sensitivity did not differ from 3 SD minimal detectable concentration (MDC). The linearity was good in the range from 3.1-1930 pg/ml. Comparison with the IRMA used in our laboratory was analyzed by Passing-Bablok and Bland-Altman plots and revealed a proportional bias of +/-60% (slope: 1.58; IC: 1.53 to 1.63) and a systematic bias of -3.3 pg/ml which should not have any clinical consequence in the interpretation of the results. We established a reference range based on our hospital population. We evaluated 87 subjects without abnormality of calcium metabolism and with normal vitamin D supply. Three groups of patients were also analyzed: 57 patients with vitamin D insufficiency, 17 with renal failure and 15 with hypercalcemia (7 due to primary hyperparathyroidism and 8 due to another etiology). Reference ranges were from 10.2 to 93 pg/ml for CLIA measurement and from 6.4 to 68 pg/ml for IRMA measurement. PTH values measured by CLIA varied from 6 to 142 pg/ml in patients with vitamin D insufficiency. By CLIA measurement, intact PTH was between 26 and 892 pg/ml in renal failure, between 54 and 201 pg/ml in primary hyperparathyroidism and between 0 and 29 pg/ml in patients with another etiology of hypercalcemia. The results of PTH measurements in EDTA plasma did not differ significantly from those performed in serum (Passing Bablock).     

Monoclonal immunoradiometric assay of calcitonin improves investigation of familial medullary thyroid carcinoma

Calcitonin (CT) assay is essential for recognizing medullary thyroid carcinoma (MTC), particularly occult familial MTC. In previous radioimmunoassays of calcitonin, polyclonal antibodies were used. Here we evaluate a new two-site immunoradiometric assay (IRMA) of calcitonin based on use of monoclonal antibodies. We assayed samples from healthy subjects, patients with renal failure, and subjects from families affected by MTC. Basal values for healthy subjects were all less than 10 ng/L. Renal failure is associated with increased basal CT. The CT peak under pentagastrin stimulation in healthy patients was less than 30 ng/L. In familial screening, basal values greater than 10 ng/L or peak values greater than 30 ng/L correspond to subjects with histologically confirmed MCT or micro-MCT. Polyclonal RIA performed in the same subjects failed to detect the moderate increase of CT that IRMA demonstrated. Preliminary results indicate that this new method may allow earlier detection of CT increase and thus improved diagnosis of MCT, particularly in familial screening. Monitoring surgical patients could also be improved by this new assay.     

Two-site assay of intact parathyroid hormone in primary hyperparathyroidism: studies in basal conditions, following adenoma removal and during calcium and EDTA infusion

This study has been carried out in order to investigate parathyroid hormone secretion in patients with primary hyperparathyroidism in basal conditions, during stimulation and suppression tests and following successful surgery. Parathyroid gland secretory activity has been evaluated by a highly sensitive immunoradiometric assay (IRMA) which detects only the biologically intact active hormone and with a well established midmolecule (MM) PTH RIA. There was a good correlation between the two assays in basal state (r = 0.779); however the correlation found between serum PTH levels and total calcium values was better for the intact hormone (P < 0.001) than for the radioimmunoassay (P < 0.05). Twenty-four hours following surgery, serum intact PTH levels were in all patients < 10 pg/ml while midmolecule PTH was still detectable, thereafter remaining at a higher level during the next six days. Serum IRMA PTH levels fell rapidly in response to the increase in serum calcium, then there was a trend to reach a plateau; serum midregion PTH levels fell, although slower than those of intact hormone. The percent increase obtained for serum intact hormone levels was higher than that observed for MM RIA, following EDTA stimulation. The results obtained indicate that the assays of intact and midmolecule parathyroid hormone clearly reflect different aspects of hormone metabolism ‘in vivo’ and may prove therefore to be useful for its investigation in various calcium disorders.     

Superiority of dynamic over static reference intervals for intact, midmolecule, and C-terminal parathyrin in evaluating calcemic disorders.

We compared the clinical performance of assays of intact, C-terminal, and midmolecule parathyrin (PTH), when used with either a dynamic reference interval (based on the range of serum PTH concentrations observed in 35 healthy individuals during acute modifications of their blood calcium concentrations) or a gaussian (mean +/- 2 SD) interval derived from normocalcemic individuals. Dynamic intervals were substantially different from gaussian intervals, with half of the area delimited by the gaussian limits for calcium and intact PTH concentrations, and one-third for both C-terminal and mid-PTH assays, being outside the range of values observed during the dynamic tests. Use of the dynamic intervals increased the average clinical sensitivity of the three assays for detecting primary hyper- and hypoparathyroidism from 68% to 97% (and up to 100% for the intact and C-PTH assays). Even though only the intact PTH assay allowed complete separation between primary hyperparathyroid and nonparathyroidal hypercalcemic patients, the average proportion of patients correctly classified in this latter category was increased from 40% to 70% by the use of dynamic intervals. We conclude that gaussian reference intervals are largely responsible for the poor clinical sensitivity of many types of PTH immunoassays and that they should be replaced by dynamic reference intervals when evaluating calcemic disorders.     

Potential clinical utility of a new IRMA for parathyroid hormone in postmenopausal patients with primary hyperparathyroidism

BACKGROUND: A new commercially available (so-called second-generation) IRMA for parathyroid hormone (PTH) separately detects intact PTH and its N-truncated fragments; however, no studies have compared the first- and second-generation IRMAs for PTH in patients with primary hyperparathyroidism (PHPT) to assess their respective diagnostic accuracies. METHODS: We concomitantly investigated 39 postmenopausal patients with PHPT and a control group of 70 healthy postmenopausal women matched for age, renal function, and vitamin D status. In all individuals, PTH was measured with a classic IRMA (PTH-S; DiaSorin Inc.), which uses antibodies directed against epitopes 1-34 and 39-84, and a new method (Scantibodies Laboratory. Inc.), which uses antibodies against epitopes 1-4 and 39-84 (PTH-W) and epitopes 7-34 and 39-84 (PTH-T). We also assayed serum PTH in 10 PHPT patients every 24 h for 5 days after successful surgery. RESULTS: The different assays gave serum PTH values that were >2 SD higher than values for the control population in 59% (PTH-S), 77% (PTH-W), and 82% (PTH-T) of patients with PHPT. However, ROC curve analysis showed no significant differences among the three PTH assays, demonstrating overlapping diagnostic sensitivities. In PHPT patients, the correlation among the assays was highly significant (r = 0.91-0.92; P <0.001). The ratio PTH-W:PTH-T x 100 showed a gaussian distribution in both PHPT patients and controls, whose mean (SD) values [63.4 (13.3)% vs 64.5 (9.5)%, respectively] did not differ significantly. After parathyroidectomy, the mean percentages of variation in PTH detected with all of the assays were quite similar. CONCLUSIONS: The distribution of the PTH-W:PTH-T ratio in patients and controls suggests that PHPT does not markedly influence the rate at which biologically inactive fragments are generated by central or peripheral cleavage of PTH. The similar postoperative curves seem to contradict the hypothesized effect of acute hypocalcemia in modulating the central secretion of hormonal fragments. Our results indicate that the three investigated assays have similar diagnostic sensitivities in PHPT.     

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.     

Monoclonal immunoradiometric assay and polyclonal radioimmunoassay compared for measuring neuron-specific enolase in patients with lung cancer.

Neuron-specific enolase (NSE) is the most sensitive and specific tumor marker for small-cell lung cancer (SCLC). We evaluated a new monoclonal IRMA (Sangtec) for NSE and compared it with a polyclonal RIA (Pharmacia) in patients with SCLC or other lung cancers (NSCLC). We measured NSE concentrations in 100 healthy subjects (NI group), 100 patients with benign pulmonary diseases (BPD group), and 194 patients with advanced lung cancer (97 SCLC and 97 NSCLC). Intra- and interassay CVs were less than 7% for both assays, and dose-dilution curves paralleled their respective standard curves. Values measured by both assays were highly correlated in all groups. NSE concentrations were significantly (P less than 0.001) lower by IRMA than by RIA in NI and BPD groups. The upper 95th percentile values for NSE in the NI group were 11.7 micrograms/L in the RIA and 9.2 micrograms/L in the IRMA. In NSCLC, the values were significantly (P less than 0.05) lower by IRMA but the percentage of subjects with increased values was higher (vs the NI group, 31% for RIA and 44% for IRMA, P less than 0.005). Diagnostic sensitivity for SCLC was improved with IRMA: 83% of values with RIA and 93% with IRMA were increased above the NI group values (P less than 0.005); the corresponding values for SCLC vs BPD were 81% and 89% (P less than 0.05). NSE values measured in 39 patients with SCLC after chemotherapy were more often increased and were significantly higher with the IRMA than with the RIA (P less than 0.005).     

Modified immunoradiometric assay of parathyroid hormone-related protein: clinical application in the differential diagnosis of hypercalcemia.

We have developed a sensitive, specific solid-phase immunoradiometric assay (IRMA) of parathyroid hormone-related protein (PTH-RP) with use of affinity-purified polyclonal immunoglobulins. Antibodies recognizing PTH-RP(37-74) are immobilized to a polystyrene bead to "capture" analytes from the sample; antibodies to epitopes within the 1-36 amino acid region of PTH-RP are labeled with 125I. This IRMA recognizes PTH-RP(1-74) and PTH-RP(1-86) equivalently, but does not detect N-terminal or C-terminal fragments of PTH-RP, intact human parathyrin (PTH), or fragments of PTH. PTH-RP is not stable in plasma at 3-5 degrees C or room temperature, but a mixture of aprotinin (500 kallikrein units/L) and leupeptin (2.5 mg/L) improves PTH-RP stability in blood samples. In plasma collected in the presence of these protease inhibitors from normal volunteers and patients with various disorders of calcium metabolism, PTH-RP concentrations were above normal (greater than 1.5 pmol/L) in 91% (42 of 46) of patients with hypercalcemia associated with nonhematological malignancy. In plasma from patients with other hypercalcemic conditions (e.g., primary hyperparathyroidism, sarcoidosis, and vitamin D excess), PTH-RP was undetectable. Above-normal concentrations of PTH-RP and total calcium decreased to normal in a patient with an ovarian cyst adenocarcinoma after surgical removal of the tumor. We conclude that PTH-RP is related to and probably the causative agent of hypercalcemia in most patients with cancer, and that measurements of PTH-RP are useful in the diagnosis and management of patients with tumor-associated hypercalcemia.     

Performance of an immunoradiometric assay of erythropoietin and results for specimens from anemic and polycythemic patients.

We evaluated a new commercially available two-site immunoradiometric assay (IRMA; BioMérieux 125I-EPO CoatRIA) for erythropoietin (EPO) in human serum. The precision (CV) was 4.1% intra-assay and 8% interassay for a serum pool with an EPO concentration of 17 int. units/L; the detection limit was 0.5 int. unit/L, one order of magnitude lower than by classical radioimmunoassay (RIA), although standardization of IRMA and RIA were similar. Results by both IRMA and RIA are compared for normal subjects, patients with nonrenal noninflammatory anemias, patients with beta-thalassemia major, hemodialysis patients, and patients with primary or secondary polycythemia. Values by IRMA compared well with those by RIA in the upper area of the range; IRMA and RIA values for EPO show parallel expected variations with the degree of anemia. However, because of its greater sensitivity and specificity, we consider the IRMA more appropriate than RIA for investigating patients with sub-normal EPO concentrations.     

Intraoperative parathyroid hormone analysis: A study of 200 consecutive cases

BACKGROUND: Immunoassays for parathyroid hormone (PTH), with short incubation times and results available in <15 min, have allowed intraoperative monitoring of the success of parathyroid surgery. The purpose of this study was to evaluate the analytical performance of a rapid PTH assay and its clinical performance in a series of 200 patients. METHODS: PTH was measured with a modified immunochemiluminometric assay with a 7-min incubation time (QuiCk-IntraOperative(TM) Intact PTH assay). The rapid assay was compared with results in a central laboratory (immunoradiometric assay) in 44 EDTA-plasma specimens. The rapid assay was used intraoperatively in 200 consecutive cases with specimens analyzed before and 5-10 min after resection of the hypersecreting parathyroid gland(s). RESULTS: Intraassay imprecision was 12% at 28 ng/L and 11% at 278 ng/L. Regression analysis of results of the rapid PTH assay and the IRMA PTH assay in 44 parathyroidectomy patients yielded y = 1.26x - 12 ng/L, S:(y|x) = 26.3 ng/L, r = 0.984, and in 40 of 44 patients with values <200 ng/L, y = 1.02x + 1.9, S:(y|x) = 13.9, r = 0.947. In the 195 cases using intraoperative PTH testing with complete results and defined clinical outcomes, the overall accuracy of the assay in predicting surgical success was 88% using the criterion of a 50% decrease at 5-10 min and 97% including the subset of patients with delayed decreases of PTH. CONCLUSIONS: The rapid PTH assay had excellent analytical performance and excellent agreement with the PTH immunoradiometric assay and predicted the success of parathyroid surgery in this large series of consecutive patients.     

Measurement of corticotropin in unextracted plasma: comparison of a time-resolved immunofluorometric assay and an immunoradiometric assay, with use of the same monoclonal antibodies

We describe a time-resolved immunofluorometric assay (IFMA) for corticotropin in unextracted human plasma, based on the use of two monoclonal antibodies: europium-labeled antibody 1A12 and antibody 2A3 coated onto microtiter wells. We compared the results of this assay with those of an immunoradiometric assay (IRMA) performed with the same antibodies working ranges (CV less than 10%) were 25 to 1000 ng/L and 22 to 1000 ng/L for the IFMA and IRMA, respectively, and both assays had comparable detection limits (IFMA 4.0 +/- 1 ng/L, IRMA 3.5 +/- 0.8 ng/L). Results by both assays for 130 patients' samples containing corticotropin within the range 3-100 ng/L and greater than ng/L correlated well (r = 0.88 and 0.92, respectively), and samples with corticotropin in the range 80-624 ng/L gave results that paralleled those for the standard curve. Corticotropin concentrations in apparently healthy subjects were consistent with those reported previously. The IFMA is a simple, precise, and robust assay that can be completed within one day. Its nonisotopic label is stable for at least 50 weeks.     

Clinical evaluation of two novel biointact PTH(1–84) assays in hemodialysis patients

Objectives

In chronic kidney disease–mineral and bone disorder (CKD-MBD), most treatment decisions are guided by parathyroid hormone (PTH) levels. Here, we aimed at assessing the technical and clinical performance of two novel automated biointact PTH(1–84) assays, from Roche Diagnostics (Ro) and DiaSorin (DS), in hemodialysis patients.

Design and methods

We recorded demographics, dialysis treatment characteristics, pharmacotherapy for CKD-MBD and laboratory work-up. Statistical methods included Passing–Bablok, and multiple linear regression.

Results

121 patients, dialyzing on average for 3.5 years (range: 0.1–22.5), with serum phosphate 1.9 ± 0.6 mmol/L (mean ± SD), participated in the study. Median serum concentration for intact PTH was 223 ng/L (range: 5–2844), and for biointact PTH(1–84) was 136 ng/L (Ro; range: 1–1644), respectively 138 ng/L (DS; range: 4-1580). Both biointact assays were significantly correlated (r = 0.98; Ro = 0.87 × DS + 19.60). Bland–Altmann plots revealed an average bias ± 2 SD of 10 ± 27 ng/L below 200 ng/L, and − 32 ± 157 ng/L above 200 ng/L (Ro minus DS). The variably adjusted association between PTH and serum phosphate was very similar, regardless of the PTH assay, but this was not the case for PTH-derived measures (ratios biointact/intact; differences intact minus biointact). (Log)PTH concentrations as well as serum phosphate were significantly associated with serum creatinine, but only in patients with > 0 mL urine per day.

Conclusions

Results from Roche and DiaSorin biointact PTH(1–84) assays were well correlated, but showed increased deviations at higher concentrations. Biointact PTH(1–84) levels are roughly two third of intact PTH. The association between PTH and serum creatinine may depend on residual renal clearance of PTH and/or serum phosphate.     

Hypocalcemia and parathyroid hormone secretion in critically ill patients

OBJECTIVE: To investigate possible causes of hypocalcemia and to assess parathyroid hormone (PTH) secretion in intensive care unit (ICU) patients. DESIGN: Combined cross-sectional and prospective study. SETTING: ICU in a university hospital. PATIENTS: Thirteen patients with sepsis and 13 patients who underwent major surgery. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Calcium metabolic indices were investigated during the first 24 hrs in the ICU and after 2 days. Eight of the surgical patients and five of the septic patients were subjected to a citrate/calcium infusion on day 1 in the ICU, to study the dynamics of PTH secretion. The blood ionized calcium (Ca2+) concentration was generally low in the septic patients (mean +/- SD, 1.03+/-0.08 mmol/L; reference value, 1.10-1.30) and increased, but not normalized, after 2 days. Hypocalcemia was only occasionally seen in the surgical patients. In the septic patients, urinary excretion of calcium was low; and, in both patient groups, elevated concentrations of two markers of bone resorption, deoxypyridinoline and ICTP (serum carboxy-terminal cross-linked telopeptide of type I collagen), were found. In cases of sepsis, the concentrations of proinflammatory cytokines were high (394+/-536 pg/mL for tumor necrosis factor-alpha and 5676+/-5190 pg/mL for interleukin-6, both normally <10-20). The Ca2+ concentration was inversely related to tumor necrosis factor-alpha and interleukin-6 (r2 = .35-.42; p<.01), as well as to procalcitonin (r2 = .71; p<.01). Despite normocalcemia in the surgical patients, serum PTH concentrations were elevated in both patient groups (97 and 109 ng/L) (reference value, <55 ng/L), both on day 1 and day 3 in the ICU. The citrate/calcium infusion revealed an increased secretory response of PTH to lowered Ca2+ concentrations in both groups of patients (p<.05), when compared with matched healthy controls. CONCLUSION: Hypocalcemia was common in septic ICU patients and was not the result of an increased urinary excretion of calcium or of an attenuated bone resorption, but seemed related to the inflammatory response. An increased PTH secretion was found in both patient groups.