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

Agreement of Parathyroid Hormone Status Measured by Intact and Biointact Parathyroid Hormone Assays among Chronic Kidney Disease Patients and Its Correlation with Bone Turnover Parameters

Background

This study aimed to determine the agreement between intact parathyroid hormone (iPTH) and biointact parathyroid hormone (bio-PTH) assays and to correlate them with bone markers.

Methods

This cross-sectional study included 180 patients with chronic kidney disease (CKD) stages 3b, 4 and 5D. We measured their iPTH, bio-PTH, 25-hydroxyvitaminD (25(OH)D), C-terminal telopeptide collagen (CTX), procollagen 1 intact N-terminal propeptide (P1NP), calcium, phosphate and alkaline phosphatase (ALP).

Results

Higher iPTH than bio-PTH concentrations were seen in CKD stages 3b, 4 and 5D (58[62] versus 55[67] pg/mL, 94[85] versus 85[76] pg/mL and 378[481] versus 252[280] pg/mL, respectively). Both PTH assays showed good agreement among all the subjects, with an intraclass correlation coefficient of 0.832 (P-value < 0.001). The Passing-Bablok showed that the equation for the bio-PTH was PTH = 0.64 iPTH + 15.80, with r = 0.99. The Bland-Altman plots showed increased bias with an increasing PTH concentration. Both PTH assays showed a high positive correlation with CTX and P1NP, a moderate correlation with phosphate, a low correlation with ALP and calcium, and a negligible correlation with phosphate and 25(OH)D.

Conclusion

The iPTH and bio-PTH assays were in agreement, but their bias increased with the PTH concentration. The unacceptable large bias indicates that the two assays cannot be used interchangeably. They had a variable correlation with the bone parameters.

Preanalytical considerations in parathyroid hormone measurement

Automated immunoassays used to evaluate parathyroid function are vulnerable to different types of interference, which can affect clinical practices. This review provides a detailed overview of the six main types of interference known to affect the measurement of parathyroid hormone (PTH): heterophilic antibodies, biotin, PTH fragments, oxidized PTH (oxPTH), phosphorylated PTH, and some preanalytical factors. Because the prevalence of some of these conditions has been reported to approach 11.7%, and the frequency of testing for parathyroid function is important, the scale of the problem might be tremendous. Potential interference in parathyroid function testing should always be suspected whenever clinical or biochemical discrepancies arise. Their identification typically relies on additional laboratory tests, including method comparison, serial dilution, blocking reagent studies, affinity adsorption, and polyethylene glycol precipitation. Moreover, some of these issues can be mitigated with the development of mass spectrometry. This review also evaluated the clinical impact of parathyroid interference on immunoassays, including misdiagnosis, inappropriate parathyroidectomy; and delay in receiving appropriate therapy. Hence, strong communication should be maintained between the clinician and laboratory to avoid such scenarios.

Should clinical laboratories adapt to the reality of chronic kidney disease in the determination of parathyroid hormone?

Objectives

The contribution of the clinical laboratory to diagnostics is increasingly important since a great deal of clinical decisions rely on laboratory test results.

Content

Parathyroid hormone (PTH) measurement presents a considerable analytical variability due to the heterogeneity of its circulating forms and the antigenic configuration of the different assays commercially available. Such variability may have an impact on pathological conditions associated with significant increases in circulating PTH, as it is the case of chronic kidney disease (CKD).

Summary

Despite the recent identification of new molecules involved in bone and mineral disorders associated with CKD, such as klotho or the fibroblastic factor 23 (FGF23), nephrologists still base their clinical decisions on PTH concentrations. The problem is that unawareness of these analytical considerations may cause errors in the clinical interpretation of test results.

Outlook

This systematic review addresses these issues from the clinical laboratory perspective and proposes new approaches related to PTH method selection and result expression. These new strategies will help laboratory medicine specialists and nephrologist better determine the status of CKD patients.

Parathyroid Hormone Concentrations in Maintenance Hemodialysis: Longitudinal Evaluation of Intact and Biointact Assays

Rationale & Objective

Management of chronic kidney disease mineral and bone disorder requires parathyroid hormone (PTH) concentrations. “Biointact” PTH immunoassays detect “whole” PTH (wPTH), whereas “intact” immunoassays measure PTH plus PTH fragments (iPTH). We aimed to determine whether longitudinal changes in PTH concentrations can be evaluated using biointact and intact immunoassays alike.

Study Design

Open noninterventional longitudinal cohort study.

Setting & Participants

PTH concentrations were measured quarterly up to 5 times in 102 hemodialysis patients.

Predictors & Tests Compared

Age, sex, phosphate levels, and others as clinical predictors for PTH trend. Tests compared were iPTH immunoassays from Siemens and Roche and wPTH immunoassays from Roche and DiaSorin.

Outcomes

PTH concentration trend; regression equations; test bias.

Analytical Approach

Predictive regression-to-the-mean model for PTH slope; Bland-Altman plots, Passing-Bablok regression, and reference change values for test comparisons.

Results

wPTH concentrations were similar with both immunoassays (wPTH-Roche = 11.7 + 0.97 × wPTH-DiaSorin, r = 0.99; mean ± 1.96 SD bias, 8.2 ± 43.3 pg/mL [17.5% ± 40.9%], by Bland-Altman plots). iPTH-Siemens concentrations were higher than iPTH-Roche concentrations (iPTH-Siemens = −5.4 + 1.33 × iPTH-Roche, r = 0.99; mean ± 1.96 SD bias, 84.0 ± 180.2 pg/mL [21.1% ± 29.8%], by Bland-Altman plots). iPTH-Roche and iPTH-Siemens concentrations were 2- and 2.5-fold higher than wPTH concentrations, respectively. Full agreement among all 4 immunoassays in detecting both significant and insignificant changes in PTH concentrations, upward or downward from one quarter to the next, was reached in 87% of consecutive measurements. In a predictive model, baseline PTH concentrations > 199 pg/mL (wPTH-Roche), 204 pg/mL (wPTH-DiaSorin), 386 pg/mL (iPTH-Roche), and 417 pg/mL (iPTH-Siemens) correctly predicted declining PTH concentration trend in 62% to 68% of patients, but age, sex, hemodialysis vintage, and calcium and phosphate levels were no significant predictors.

Limitations

Limited number of immunoassays, only 59 patients attended all quarterly samplings.

Conclusions

wPTH-Roche and wPTH-DiaSorin concentrations were similar, while iPTH was higher than wPTH concentrations. The iPTH-Siemens immunoassay is either higher calibrated or detects more fragments than iPTH-Roche. However, longitudinal PTH concentration changes largely coincided with all tested immunoassays.

The path to the standardization of PTH: Is this a realistic possibility? a position paper of the IFCC C-BM

Parathyroid hormone (PTH) determination is of greatest importance for patients suffering from parathyroid gland disorders and for the follow-up of bone turnover in patients suffering from chronic kidney disease (CKD). Two generations of PTH assays are simultaneously present on the market for PTH quantification. As these assays are not yet standardized, this results in a significant level of confusion in the care of CKD patients. One key objective of the IFCC Committee for Bone Metabolism is to improve this situation. In this position paper, we will highlight the current state of PTH testing and propose a pathway to ultimately overcome issues resulting from PTH assay variability.

PTH: Redefining Reference Ranges in a Healthy Population-The Role of Interfering Factors and the Type of Laboratory Assay

Introduction. Parathyroid hormone (PTH) is a linear peptide constituted by 84 amino acids and active in its 1-84 form, but a wide range of PTH forms produced by its post-transcriptional modifications are present in blood. Many assays with different specificities are commercially available. The aim of our study was to compare a 2^nd and 3^rd generation in healthy population in order to better define the reference range in the healthy population residing in our region. Materials and Methods. 108 subjects (53 females and 55 males) referring to the transfusion donor were enrolled in the study centre in April 2016 and underwent PTH levels measurements with a 3^rd generation kit (chemiluminescent immunoassay DiaSorin Liaison) and with a 2^nd generation kit (immunoradiometric assay Total Intact PTH Assay (Coated Tube), Scantibodies). Also calcium, phosphate, creatinine, and 25OHD3 were measured. A questionnaire on lifestyle and dietary habits was obtained.

RESULTS

The median PTH values obtained with the 2^nd generation assay and the whole 3^rd generation assay were 20.26 pg/ml and 23.11 pg/ml, respectively. Bland-Altman method showed substantial concordance between the two PTH assays, although with an overestimation of the 3^rd generation method over the 2^nd generation method. There was no correlation between 3^rd generation PTH and 25OHD3 and creatinine. Calcium was negatively correlated with PTH only when measured with 3^rd generation kit.

CONCLUSIONS

On the basis of our data, obtained from healthy subjects, we can conclude that the reference range used by our laboratory was too narrow and was necessary to reestablish normal ranges according to our population. This is useful to avoid hyperparathyroidism misdiagnosis.

Parathormone Levels in a Middle-Eastern Healthy Population Using 2nd and 3rd Generation PTH Assays

BACKGROUND

The purpose of the current study is to determine PTH reference values in vitamin-D-replete Lebanese adults using 2^nd and 3^rd generation PTH assays and to look at the factors that affect PTH variations.

METHODS

Fasting PTH was measured using 2^nd and 3^rd generation Diasorin PTH assays in 339 vitamin-D-replete healthy subjects aged 18 to 63 years (230 men and 109 women) who have normal calcium levels and an eGFR ≥60 ml/mn. 25-OH vitamin D (25(OH)D) was measured using the Diasorin assay.

RESULTS

For the 2^nd PTH generation, median (IQR) levels were 48.9 (34.9-66.0) pg/ml, and its 2.5^th-97.5^th percentile values were 19.7-110.5 pg/ml for 25(OH)D values between 20 and 30 ng/ml, and 19.7-110.7 pg/ml for 25(OH)D values ≥30 ng/ml. For the 3^rd PTH generation, the median (IQR) values were 23.9 (17.7-30.5) pg/ml, and its 2.5^th-97.5^th percentile values were, respectively, 9.2 and 50.2 pg/ml for 25(OH)D values between 20 and 30 ng/ml, and 8.4 and 45.4 pg/ml for 25(OH)D values ≥30 ng/ml. The median (IQR) serum 25(OH)D levels were 27.5 (23.8-32.7) ng/ml. 2^nd and 3^rd generation PTH values are strongly correlated (r = 0.96, p < 0.0001), but poorly concordant (Lin's concordance coefficient 0.365, 95% CI: 0.328-0.401) with observations beyond the 95% Bland-Altman limits of agreement. 2^nd and 3^rd generation PTH levels did not differ according to gender and were significantly correlated with age but not with 25(OH)D and serum calcium levels.

CONCLUSION

Lebanese adult healthy subjects have higher 2^nd and 3^rd generation PTH levels compared with the reference range provided by the manufacturer. The reference range was not influenced by changing the 25(OH)D cutoff. The clinical significance of the higher PTH levels in our population should be investigated.

Moving from the second to the third generation Roche PTH assays: what are the consequences for clinical practice?

Background The determination of parathyroid hormone (PTH) is essential for exploring phosphocalcic disorders especially in patients with renal failure. At present, second or third generation PTH assays are available on the market from Roche Diagnostics as well as from others companies but the lack of standardization has complicated the interpretation. Methods We wanted to assess the clinical impact by measuring the PTH levels with the two generations concomitantly on different groups of populations including 46 healthy, 103 pre-dialyzed and 73 hemodialyzed (HD) patients. Results In healthy subjects, the PTH concentrations were not different whatever the generation used, whereas beyond 200 pg/mL, we reported an overestimation of the second generation PTH. In patients with chronic kidney disease (CKD) stage 3-5 the observed differences between the two generations increase with increasing PTH levels and decreasing glomerular filtration rate (GFR). Classification according to the kidney disease: improving global outcomes (KDIGO) revealed a high percentage of discordant results between the two generations (κ coefficient <0.20). These discrepancies are clinically relevant as PTH levels remain the cornerstone for diagnosis and treatment of the CKD-mineral and bone disorder (CKD-MBD). Conclusions The introduction of a new PTH assay generation in clinical practice should be carried out with caution.

PTH assays in dialysis patients: Practical considerations

Parathyroid hormone (PTH) 1-84 is the main biologically active hormone produced by the parathyroid cells. Circulating PTH molecules include the whole PTH 1-84 along with amino (N) and carboxyl (C) terminal fragments. While PTH is the best available noninvasive biomarker to assess bone turnover in dialysis patients, the biological roles of individual circulating PTH fragments are still not completely known. The understanding that there is an enormous variation in the target specificity of currently available PTH assays for different circulating forms of PTH has led to the evolution of assays from first to second then third generation. With a reduction in kidney function, there is a preferential increase in circulating C fragments and non-PTH 1-84 forms, resulting in a decrease in the ratio of PTH 1-84/non-PTH 1-84. However, there are also substantial differences in between-assay measurements, with several fold variations in results. Targets based on multiples of the upper limit of normal (ULN) should be used rather than PTH ranges using absolute iPTH values. To date, the second-generation PTH remains the most widely used assay. Current guidelines recommend following iPTH trends rather than absolute values. Herein, we highlight problems and challenges in PTH assays/measurements and their interpretations in dialysis patients.

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.

Comparing the values of intact parathormone and 1– 84 PTH to predict hyperparathyroidism in hemodialysis patients

Background:

Secondary hyperparathyroidism (SHPT) is a common complication of chronic kidney disease (CKD) leading high mortality and even long-term morbidity. SHPT is manifested by elevation of parathyroid hormone (PTH) and accurate determining the level of serum PTH is very essential for early diagnosis of SHPT secondary to CKD. It is very important to match the values obtained for intact parathormone (iPTH) and 1– 84 PTH with the minimized measurement bias.

Objectives:

The present study aimed to first determine the agreement value between the iPTH and 1– 84 PTH measures in patients with hyperparathyroidism secondary to endstage renal disease under chronic hemodialysis. Then, we attempted to determine the best cutoff values for these two measurements for detecting SHPT in such patients.

Patients and Methods:

This cross-sectional study was conducted on hemodialysis patients. The value of study biomarkers including iPTH and 1– 84 PTH was assessed.

Results:

A strong positive association was revealed between the two indicators of iPTH and 1-84 PTH (r = 0.800, P < 0.001). The linear association between these two parameters is independent to baseline characteristics including gender, age, body mass index, and medical history. Among all biochemical elements, the value of 1-84 PTH was only associated with serum calcium level negatively (r = -0.267, P = 0.027) and alkaline phosphatase positively (r = 0.359, P = 0.003). Considering iPTH as the reference and according to the area under the ROC curve (AUC), 1-84 PTH had high value to predict hyperparathyroidism (AUC = 0.926, P < 0.001). The best cutoff point for 1-84 PTH to discriminate hyperparathyroidism from normal condition was 60 yielding a sensitivity of 92.3% and a specificity of 79.1%. Among other baseline laboratory parameters, only alkaline phosphatase had an acceptable value for diagnosing hyperparathyroidism (AUC = 0.731, P = 0.001).

Conclusions:

The measurement of both iPTH and 1-84 PTH is valuable for predicting hyperparathyroidism secondary to CKD, but according to lower cost and comparableeffectiveness of iPTH measurement, this assay may be comparable to 1-84 PTH to predict this consequence.

The relationship between intact PTH and biointact PTH (1-84) with bone and mineral metabolism in pre-dialysis chronic kidney disease (CKD)

OBJECTIVES

Abnormalities in PTH are implicated in the pathogenesis of bone abnormalities in chronic kidney disease (CKD)-mineral bone disorder (CKD-MBD). PTH concentrations are important in clinical decision and management. This emphasises the importance of providing an assay which measures biologically active PTH. We compared concentrations of intact PTH with biointact PTH (1-84) in CKD and end stage renal disease (ESRD) and investigated the relationship between the 2 PTH assays with bone and mineral laboratory parameters and bone mineral density (BMD) in CKD.

DESIGN AND METHODS

We assessed 140 patients (61 in ESRD and 79 with CKD stages 1-4) in this cross-sectional study. We measured biointact PTH (1-84) as well as routine biochemical parameters on all subjects. In the CKD cohort, bone turnover markers; bone alkaline phosphatase (BAP) and tartrate resistant acid phosphatase (TRACP)-5b and bone mineral density (BMD) were also determined.

RESULTS

In ESRD, intact PTH concentration was significantly higher compared to biointact PTH (1-84) (422 [443] v/s 266 [251] pg/mL, (p<0.001) with an average bias of 60%. In CKD, intact PTH concentration was also higher compared to biointact PTH (1-84) (79[55] v/s 68[49] pg/mL p<0.001) with an average bias of 18%. Only the biointact PTH (1-84) assay showed any significant correlation with serum calcium concentrations (r=-0.26, p<0.05) and phosphate (r=0.25, p<0.05) in CKD. Following multilinear regression analysis and adjustment for all significant co-variables, only eGFR, BAP and 25 (OH)vitamin remained significantly associated with intact PTH and biointact PTH (1-84). The strength of association was stronger between BAP and biointact PTH (1-84) (biointact PTH (1-84): p=0.007, intact PTH: p=0.01). In adjusted analyses, only biointact PTH (1-84) was significantly associated with BMD at the fore-arm (FARM) (p=0.049).

CONCLUSIONS

The study confirms the differences between intact PTH and biointact PTH (1-84) in ESRD. Whilst there may be similarities in the diagnostic ability of both intact and biointact PTH (1-84), our data suggest that biointact PTH (1-84) assay may better reflect bone metabolism and BMD in CKD. Further longitudinal studies are needed.

Comparison of the Elecsys PTH(1-84) assay with four contemporary second generation intact PTH assays and association with other biomarkers in chronic kidney disease patients

OBJECTIVES

The COBAS Elecsys PTH(1-84) assay is a novel, electro-chemiluminescence immunoassay that exclusively measures full-length parathyroid hormone (PTH). The aim of this study is to compare the automated biointact Elecsys PTH(1-84) assay with four contemporary, iPTH assays in chronic kidney disease (CKD) patients.

DESIGN AND METHODS

We compared the Elecsys PTH(1-84) assay with four iPTH assays (Siemens ADVIA Centaur, Ortho Clinical Diagnostics (OCD) VITROS, Beckman Access2, Abbott ARCHITECT) in the measurement of PTH in 83 local CKD patients. Majority of the patients (44) had CKD but were not on dialysis, 15 were on hemodialysis, 15 were on peritoneal dialysis, and 9 were post-renal transplant. The precision performance and correlation of the assays were determined. PTH(1-84) concentrations were correlated with calcium, phosphate, alkaline phosphatase, hemoglobin, HbA1c and lipid concentrations.

RESULTS

The Elecsys PTH(1-84) assay showed comparable precision and good correlation with the iPTH assays. Although the four different iPTH assays correlated well with each other, there was significant discrepancy among assays. The discrepancy among assays increased with increasing PTH concentrations. The ADVIA Centaur and ARCHITECT assays measured significantly higher PTH concentrations than the VITROS and Access2 assays. PTH(1-84) showed a positive association with phosphate and alkaline phosphatase and an inverse association with HbA1c. There was no significant association with lipid concentrations.

CONCLUSIONS

The third generation Elecsys PTH(1-84) assay had comparable precision performance and correlated well with second generation iPTH assays. However, significant discrepancy was found among the four iPTH assays in measuring iPTH in CKD patients.