Higher parathyroid hormone (PTH) concentrations with the Architect PTH assay than with the Elecsys assay in hemodialysis patients, and a simple way to standardize these two methods

Parathyroid hormone measurement in chronic kidney disease: Impact of inter-method variability on mineral bone disease assessment

BACKGROUND

Parathyroid hormone (PTH) is measured routinely as part of Chronic Kidney Disease Bone and Mineral Disorders (CKD-MBD) assessment. Multiple PTH assays exist with known differences resulting in CKD-MBD guidelines recommending treatment based on assay-specific thresholds. The study objectives are to assess between manufacturer and within manufacturer variability of PTH assays and the impact of assay variability on the assessment of CKD-BMD using both vendor defined and empirically derived thresholds.

METHODS

Data were collected from Ontario, Canada's Proficiency Testing Program (24 challenge vials, 115-133 laboratories all using secondary generation PTH assays. Mean PTH and precision by the coefficient of analytical variation (CV_a) were calculated. For each vial, whether the manufacturer's mean value exceeded the vendor-defined and empirically-derived upper limit of normal (ULN) was recorded and the concordance between assays was determined.

RESULTS

Across all laboratories, the mean PTH range was 12.0 ± 3.9 pmol/L and the mean CV_a was 30%. The percent of vials with a mean PTH exceeding manufacturer's specific ULN varied substantially between manufacturers. Only 58% of vials had complete concordance as to whether mean PTH was above assay-specific ULNs. This increased to 83% using the empirically derived ULN.

CONCLUSIONS

CKD-BMD assessment and management will depend on the PTH assay. The between-assay variability is reduced but not eliminated when empirically derived reference intervals are used. Improvements in PTH measurement are required in order to ensure consistent patient care.

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.

In vitro diagnostic company recalls and medical laboratory practices: an Italian case

Introduction

In vitro human diagnostic (IVD) company recalls are a common practice aimed to either minimize a potential error or eliminate an existing failure. In this case report, we aim to provide a critical analysis of a recent IVD recall and to provide a practical framework about what to do when an IVD company recalls product(s) based on the International Organization for Standardization - ISO 15189:2012 standard.

Case report

In 2014, Abbott Laboratories® (Green Oaks, IL) published an urgent field safety notice regarding a product recall (Architect Intact parathyroid hormone (PTH) Assay List Number 8K25) with immediate action required. The IVD company explained the reasons for the recall as follows: i) Abbott has confirmed that a performance shift in the Architect Intact PTH assay has the potential to generate falsely elevated results on patient samples; ii) results generated with impacted lots may demonstrate a positive shift relative to those generated with previous reagent and/or calibrator lots. This issue may also impact established Architect Intact PTH reference ranges; iii) the magnitude of shift averages approximately 13% to 45%; iv) Abbott Architect Intact PTH controls do not detect the shift; and v) all current reagent, calibrator, and control inventory are impacted. The recall could have resulted in ~40,000 inaccurate laboratory tests reported by 18 laboratories from Italy (Lombardy region).

Conclusion

IVD company recalls have a serious impact on the patient safety and require a thorough investigation and responsible approach to minimize the possible damage. Medical laboratories accredited according to the ISO 15189 standard have procedures in place to manage such situations and ensure that patient safety is maintained when such recalls are issued.

The association between hyperandrogenemia and the metabolic syndrome in morbidly obese women

BACKGROUND

Female abdominal obesity is associated with hyperandrogenemia (HA), but few studies have addressed the possible association between HA and metabolic syndrome (MetS) among obese women. Some studies indicate that insulin resistance may cause HA through different mechanisms. On the other hand, a bidirectional relationship between HA and insulin resistance has been suggested. Thus, we aimed to investigate if morbidly obese women with HA had higher odds of MetS and its components than those without HA (controls), independent of polycystic ovarian syndrome (PCOS) status.

METHODS

This cross-sectional study comprised 1900 consecutive treatment seeking morbidly obese women <50 years. Free testosterone index (FTI) >0.6 defined HA. Women with previously diagnosed PCOS and those with oligo- / anovulation combined with clinical or biochemical hyperandrogenism were defined as having PCOS. Multiadjusted associations between HA and MetS were assessed by logistic regression analysis.

RESULTS

Out of 1900 morbidly obese women, 1089 (57 %), 846 (45 %) and 312 (16 %) had MetS, HA and PCOS, respectively. Compared with controls (without HA), women with HA were younger (34 [1] years vs. 39 [2], p < 0.001) had a higher prevalence of MetS (62 % vs. 53 %, p < 0.001), type 2 diabetes (18 % vs. 15 %, p = 0.045), low HDL-cholesterol (65 % vs. 48 %, p < 0.001) and hypertriglyceridemia (48 % vs. 41 %, p = 0.004), but a lower prevalence of raised blood pressure (53 % vs. 59 %, p = 0.014). Multivariable analyses showed that HA was associated with increased odds of MetS (OR 1.61 [95 % CI 1.27, 2.02]), dysglycemia (1.65 [1.28, 2.11]), low HDL-cholesterol (1.58 [1.27, 1.97]), and hypertriglyceridemia (1.43 [1.15, 1.79]). After stratification for the presence of PCOS, the results remained largely unchanged in women without PCOS; MetS (1.52 [1.18, 1.96), dysglycemia (1.71 [1.30, 2.25]), low HDL-cholesterol (1.55 [1.22, 1.98]) and hypertriglyceridemia (1.36 [1.06, 1.74]).

CONCLUSION

Morbidly obese women with HA had an approximately 1.5-fold increased odds of having MetS even in the absence of PCOS. Randomized controlled clinical trials, including therapeutic strategies to lower free testosterone levels, are however necessary to explore any cause-and-effect relationship.

Variability in parathyroid hormone assays confounds clinical practice in chronic kidney disease patients

BACKGROUND

Intact parathyroid hormone (iPTH) measurements are used to guide therapy in renal patients, but variability in results can occur depending on the assay used. This study has investigated iPTH assay variation in North West England and paired data with regional audit data to determine clinical relevance of assay variability.

METHODS

Thirty-seven haemodialysis patients had blood taken (EDTA plasma, and serum), and samples were processed at 17 laboratories that analyse iPTH for North West dialysis patients. Correction factors were calculated and applied to the iPTH assay results to enable direct comparisons. These correction factors were also applied to Regional Audit data to determine if iPTH assay variability explains the variation in unit performance in achieving PTH targets.

RESULTS

The iPTH results from the 37 patients were significantly different when either analysed by different assays and/or different laboratories (P < 0.001). The Abbott Architect method consistently produced the highest iPTH results. Of the 37 patients, between 49% and 65% would achieve the Kidney Disease: Improving Global Outcomes (KDIGO) iPTH target depending on the assay used. When results were adjusted using correction factors, 21% of the patients would require a change of management according to guidelines. Data from all haemodialysis units submitted for the regional audit were adjusted to the Roche assay and this led to a small change in achievement of KDIGO iPTH targets in individual units when compared to each other.

CONCLUSIONS

A combination of iPTH assay variability and diversity in clinical management leads to variation in achieving iPTH targets. Both need to be improved and/or standardized to improve patient care.

PTH--a particularly tricky hormone: why measure it at all in kidney patients?

Plasma parathyroid hormone (PTH) concentrations are commonly measured in the context of CKD, as PTH concentration elevation is typical in this clinical context. Much has been inferred from this raised PTH concentration tendency, both about the state of skeletal integrity and health and also about the potential clinical outcomes for patients. However, we feel that reliance on PTH concentrations alone is a dangerous substitute for the search for, and use of, more precise and reliable biomarkers. In this article, we rehearse these arguments, bringing together patient-level and analytical considerations for the first time.

Current parathyroid hormone immunoassays do not adequately meet the needs of patients with chronic kidney disease

BACKGROUND

There are significant differences in plasma parathyroid hormone (PTH) results obtained by current immunoassay methods. However, many clinical guidelines relevant to patients with chronic kidney disease (CKD) that recommend PTH target values do not take account of these differences. This raises major questions about the validity of the evidence underpinning current use of PTH measurements in the management of CKD as well as of published relevant audit data.

METHODS

PTH was measured in plasma from patients with CKD in six commercially available immunoassays. The initial pilot study included 19 patients while 98 patients were included in a second extended study. Data from the second study were analysed by regression analysis to obtain assay-specific targets for each immunoassay.

RESULTS

Although similar PTH reference intervals are provided by most manufacturers, both studies confirmed substantial between-method differences in observed PTH for all patients, with results varying by as much as 4.2-fold between the lowest and highest reading methods. These differences were sufficient to have treatment implications for 79% of the patients in the pilot study. Applying the assay-specific targets derived here to results from the extended study decreased treatment misclassifications from 53% to 12%.

CONCLUSIONS

Existing between-method differences in PTH measurements clearly have treatment implications. International initiatives to address these differences are in progress and will require support and input from all stakeholders. Adoption of assay-specific target values such as those reported here provides a convenient and practical interim solution that should lead to significant improvement in patient management, while also enabling meaningful audit.