Clinical Lab Handbook

Container/Tube: SST

Alternate Container: Light Green (Lith Hep), EDTA plasma, Red Top

Specimen Volume: 5 mL

Stability:

Chemiluminescence Immunoassay

An immunometric immunoassay technique is used, which involves the simultaneous reaction of PTH present in the sample with a biotinylated antibody (goat polyclonal anti‑PTH39-84) and a horseradish peroxidase (HRP)-labeled antibody conjugate (goat polyclonal anti-PTH1-34). The antigen-antibody complex is captured by streptavidin on the wells. Unbound materials are removed by washing.

The bound HRP conjugate is measured by a luminescent reaction. A reagent containing luminogenic substrates (a luminol derivative and a peracid salt) and an electron transfer agent, is added to the wells. The HRP in the bound conjugate catalyzes the oxidation of the luminol derivative, producing light. The electron transfer agent (a substituted acetanilide) increases the level of light produced and prolongs its emission. The light signals are read by the system. The amount of HRP conjugate bound is directly proportional to the concentration of PTH present.

Intact PTH is indicated to aid in the differential diagnosis of hyperparathyroidism, hypoparathyroidism, or hypercalcemia of malignancy and can be used intraoperatively.

Parathyroid hormone (PTH) is a single chain 84 amino acid polypeptide produced by the parathyroid gland. After PTH is secreted into the blood stream it undergoes extensive proteolysis to generate various fragments. In contrast to its degradation products, the concentration of Intact PTH is relatively independent of glomerular filtration rate and reflects the biologically active portion of the hormone.

The primary role of PTH is to maintain calcium homeostasis via its interaction with calcitonin. PTH measurement is an important aid in the diagnosis of disorders of calcium metabolism. PTH synthesis and secretion are triggered rapidly by low concentrations of ionized calcium (Cai). The biological activities of PTH are to increase absorption of dietary calcium, decrease renal clearance and mobilize skeletal calcium stores. Abnormally high Cai concentrations suppress secretion of PTH. In conjunction with serum calcium levels, the PTH assay may be used as an aid in the differential diagnosis of hypercalcemia, hypocalcemia and parathyroid disorders. PTH determination is important in monitoring dialysis patients to manage renal osteodystrophy.

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