Abstract
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 2nd and 3rd 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 3rd generation kit (chemiluminescent immunoassay DiaSorin Liaison) and with a 2nd 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 2nd generation assay and the whole 3rd 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 3rd generation method over the 2nd generation method. There was no correlation between 3rd generation PTH and 25OHD3 and creatinine. Calcium was negatively correlated with PTH only when measured with 3rd 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.
Highlights
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
Parathyroid hormone (PTH) is a linear peptide constituted by 84 amino acids and released by parathyroid glands. e PTH present in the circulation is very assorted, being present PTH fragments, depending from post-transcriptional modifications occurring in parathyroid cells and in other tissues, mainly in the kidneys and in the liver [1]
Afterwards, it was clarified that the N-terminal 1–34 PTH fragment is an isoform with the same biological activity of its complete 1–84 form [3], and second-generation assays were developed, nowadays the most used worldwide. ese second-generation methods consist in a noncompetitive assessment, “Sandwich” immunoassays, based on the use of two monoclonal antibodies, one directed against the N-terminal and one directed against the carboxyl amino-terminal
Summary
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. Ese second-generation methods consist in a noncompetitive assessment, “Sandwich” immunoassays, based on the use of two monoclonal antibodies, one directed against the N-terminal (aa 13–24) and one directed against the carboxyl amino-terminal (aa 39–84) These assays were thought to recognize the entire (1–84) PTH molecule, and they were considered the gold standard for PTH dosage [4]. Afterwards, assays with this specificity and commercially available were developed (third generation immunoassays) [6] This technique has its pitfalls: these types of assays are not able to distinguish the biologically active molecule from a post-translational modified form with a phosphorylated serine (aa 17) known as nontruncated amino-terminal (NT-N) parathyroid hormone (NT-N PTH) [7]. Even more problematic is to compare assays of different generations, since nowadays lots of laboratories still use secondgeneration immunoassays
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