Clinical Pathology: General Principles, Clinical Chemistry

• In the assessment of physiological states of calcium homeostasis, simultaneous measurements of ionized calcium and parathyroid hormone (PTH) should be conducted.

• The PTH molecule is a short polypeptide comprised of 84 amino acids and has a short half-life in blood of 5 minutes.

• Multiple assays are available for PTH. These include the intact PTH assay and separate assays for the biologically active amino-terminal portion of the molecule, internal PTH fragments, and the carboxyl-terminal portion of the molecule. It is important to know which assay is used for measurement of PTH.

• The intact PTH assay detects the entire molecule and is the preferred assay for measuring this molecule because it provides excellent overall sensitivity and specificity.

• The assays for PTH fragments provide improved sensitivity for the detection of disease but can be elevated under other conditions, including compromised kidney function.

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