109年年會論文摘要集

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st Annual Meeting of September 5-6, 2020 the Endocrine Society and the Diabetes Association of the R.O.C. (Taiwan)

The

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PARATHYROID HORMONE NEW ASSAYS JIN-YING LU Department Internal Medicine, National Taiwan University Hospital, Taipei , Taiwan

Parathyroid hormone (PTH) is a peptide molecule containing 84 amino acids with a molecular weight of 9,500 Daltons and is secreted by the four parathyroid glands located behind the thyroid. PTH plays a major role in the regulation of calcium and phosphate metabolism. Many disorders resulted from dysregulation of PTH secretion. Primary hyperparathyroidism due to parathyroid hyperplasia or adenoma causes increased bone resorption, hypercalcemia, and hypophosphatemia. Hypoparathyroidism as a complication of thyroid surgery results in adynamic bone disease, hypocalcemia, and hyperphosphatemia. Chronic kidney disease often hampers the excretion of phosphate and thus causes secondary hyperparathyroidism and renal osteodystrophy. The correct measurement of PTH is especially important for the diagnosis and evaluation of therapeutic effects for these disorders. The biological activity of PTH derives from the interaction between its N-terminal 34 amino acids 1-34 (PTH 1-34) and the PTH receptor. The C-terminal amino acids 7-84 (PTH 7-84) even suppresses the receptor and exerts an opposite effect to those of whole PTH. There are several different PTH N- and C-terminal fragments in normal circulation. How to measure exactly the whole length PTH and avoid the inactive fragments is the major concern of clinical laboratory. Correct measurements of different PTH fragments is crucial for the diagnosis, treatment, and prognosis of many different disorders. In clinical laboratories, the conditions of blood collection and storage, and different assay methods all affect the measurements of PTH. The first-generation immunoassay is radioimmunoassay (RIA) uses an antibody against the C-terminal PTH (c-PTH), which might detect the inactive fragments of PTH and thus has already been abandoned from clinical use. Excluding the first- generation immunoassay, in current laboratories we have two kinds of assays for the examination of PTH, the second-generation immunoassay detects the intact PTH (i-PTH) and has been thought to detect only the active form of PTH. However, it is later noted to also detect the inactive N-terminal PTH 7-84. The third-generation PTH immunoassay detects only the whole PTH (w-PTH) containing the N-terminal amino acids. However, almost all clinical laboratories still use the second-generation immunoassays to detect i-PTH, thus might lead to falsely elevated results when measuring the concentration of serum PTH levels in patients with chronic kidney disease.

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