Journées Klotz 2015Problems with the PTH assaysDifficultés de dosage de la PTH
Section snippets
The different generations of PTH assays: what they measure and what they don’t
The human parathormone (PTH) gene is located on the short arm of chromosome 11 [1]. PTH is synthesized as a large polypeptide (pre-pro PTH) containing 115 amino acids that undergoes two successive proteolytic cleavages to yield the 84 amino acids PTH, the principal form of the hormone stored in and secreted from the parathyroid glands. Its metabolization is performed in the liver, releasing different amino-truncated PTH fragments in the circulation. These fragments are generally called C
Standardisation of the PTH assays
In 1974, at its 26th meeting, the Expert Committee on Biological Standardization of the World Health Organization (ECBS, WHO), asked the National Institute for Biological Standards and Control (London), to obtain material of human origin, which could serve as an international reference preparation (IRP). In December 1978, a nominal amount of 150 μg of hPTH, stated to be more than 95% pure, was donated to WHO as a proposed IRP. Ampoules, labelled 79/500 were prepared in 1981, evaluated in a
Reference method for PTH measurement
Liquid chromatographs coupled with mass spectrometers in tandem (LCMS/MS) have recently been used for PTH quantitative analysis [28], [29]. While very sensitive, the main drawback of these techniques lies in sample preparation. Indeed, peptides as large as PTH have to undergo enzymatic digestion, followed by fragment quantification. PTH quantification is then possible, but the additional information (e.g. oxidation, new fragments, etc.) may be lost. Ideally, we need a technique selective and
Sample stability and sample type
A huge number of studies are dealing with PTH stability and a meta-analysis has recently been published on the subject [30]. The authors of this review, on behalf of the IFCC Workgroup for PTH standardization, have strongly recommended that EDTA blood samples should be taken for PTH measurement. Even if two of us (EC and JCS) are participating to this workgroup, they do not agree, for the moment, with these recommendations. Indeed, we think that the different studies on the subject present too
Problems linked with the analytical phase: heterophilic antibodies interference
Just like any other immunoassays, PTH determination is prone to heterophilic antibodies interferences. This interference, due to the presence in the serum of the patients of immunoglobulins targeted against animal proteins, can lead to falsely elevated or decreased levels of the studied parameter. These interferences can lead to significant diagnostic errors and we have shown that patients presenting human anti-goat or anti-mouse antibodies could have large discrepancies in their PTH results
Problems linked with the post-analytical phase: reference values
Establishment of reference ranges is not an easy task [34]. First, a “reference population” needs to be defined and 120 samples for each sex and/or age category have to be taken in order to establish the ranges. This task is difficult, tedious, labour intensive, time consuming and difficult to achieve in all the laboratories, reason why the ISO 15189 guidelines that rule the quality in clinical laboratories ask them to “verify” the reference ranges provided by the manufacturers. For PTH, it is
Disclosure of interest
EC is consultant at DiaSorin and IDS.
EC has received lecture fees from Shire, Amgen, Pfizer, DiaSorin, IDS, Abbott, OCD and Roche.
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2020, Handbook of Diagnostic EndocrinologySub-picomolar quantification of PTH 1-34 in plasma by UHPLC-MS/MS after subcutaneous injection of teriparatide and identification of PTH 1-33, its degradation product
2019, Journal of Pharmaceutical and Biomedical AnalysisCitation Excerpt :The pharmacokinetic (PK) parameters established during clinical trials with PTH 1-34 relied on sensitive immunoassays with lower limit of quantification (LLOQ) in the picomolar range. However, these immunoassays suffer from low specificity and the evaluation of the pharmacokinetic/pharmacodynamics relationship might be biased because of antibody cross-reactivity [5–7] such as that observed with PTH 1-84 or unknown peptide fragments. The analytical gold-standard method for the quantitative determination of PTH 1-34 plasma concentration would be ultra-high pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS), which provides a superior specificity but usually at the expense of lower sensitivity.
Establishment of reference values in a healthy population and interpretation of serum PTH concentrations in hemodialyzed patients according to the KDIGO Guidelines using the Lumipulse® G whole PTH (3rd generation) assay
2018, Clinical BiochemistryCitation Excerpt :The more recent ones are called 3rd generation assays and do not detect the non-(1–84) PTH but measure however a post-translational form called amino-PTH, that is overproduced in many patients suffering from parathyroid carcinomas [2]. Standardization of these assays is still lacking and we are still waiting for a reference method for PTH determination, as well as commutable calibrators, even if an International Standard, namely the WHO 95/646, is available [3]. In practice, results obtained with the 2nd or 3rd generation assays are not transposable, especially for CKD patients, which is most confusing for clinicians [4].
Analytical verification and method comparison of the ADVIA Centaur® Intact Parathyroid Hormone assay
2017, Clinical BiochemistryCitation Excerpt :Another important issue is the lack of comparability among iPTH assays. The use of different paired antibodies by manufactures, the lack of an accepted international standard or reference method for iPTH determinations are some of the main causes of inter-method variability [9]. In clinical practice iPTH is frequently requested to monitor CKD patients and to manage secondary hyperparathyroidism and associated mineral metabolism abnormalities.