parathyroid hormone (PTH) intact in serum/plasma

Indications

• evaluation of hypoparathyroidism
  • evaluation of hypocalcemia
• evaluation of hyperparathyroidism
  • evaulation of hypercalcemia

Reference interval

• 0.0 to 60.0 pg/mL

Principle

The Allegro Intact PTH Immunoassay is a 2 site immunoradiometric assay (IRMA) for the measurement of the biological intact 84 amino acid chain of PTH. Two different goat polyclonal antibodies to human PTH have been purified by affinity chromatography to be specific for well defined regions of the PTH molecule. One antibody is prepared to bind only the mid-region & C-terminal PTH 39-84 & this antibody is immobilized onto plastic beads. The other antibody is radiolabeled for detection.

The sample containing PTH is incubated simultaneously with an antibody-coated bead & I-125 labeled antibody. Intact PTH present in the sample is bound by both the immobilized & labeled antibodies to form a sandwich complex:

Bead Anti-PTH(39-84) - Intact PTH (1-84) - I-125 Anti-PTH(1-34

Although mid-region & C-terminal fragments are bound by the antibody coated bead, only the intact PTH 1-84 forms the sandwich complex necessary for detection. The capacity of the immobilized antibody has been adjusted to exhibit no interference by inactive fragments, even at very elevated levels. At the end of the assay incubation, the bead is washed to remove unbound components & the radioactivity bound the solid phase is measured in a gamma counter. Since the formation of a sandwich complex occurs only in the presence of an intact PTH molecule, the radioactivity of the bead bound complex is directly proportional to the amount of intact PTH in the sample.

A dose response curve of radioactivity vs. concentration is generated using results obtained from standard which are assayed concurrently with the unknowns Concentrations of intact PTH present in the controls & patient samples are determined directly from this curve.

Clinical significance

PTH plays an important role in Ca+2 homeostasis by maintain the concentration of ionized Ca+2 within the precise limits necessary to achieve metabolic & neuroregulatory functions of this essential mineral. At low levels of serum Ca+2, secondary to an inadequate assimilation of dietary Ca+2, parathyroid glands increase secretion of the hormone. This results in mobilization of Ca+2 from the large skeletal stores into the extra-cellular fluid, increased absorption of dietary Ca+2, & decreased renal clearance of urinary Ca+2. When serum Ca+2 levels increase, smaller quantities of parathyroid hormone are secreted into the bloodstream.

The measurement of PTH is an important aid in the assessment of Ca+2 metabolism disorders. When evaluated along with Ca+2 levels, the PTH values has proven useful in distinguishing normal individuals, from patients with primary hyperparathyroidism, hypoparathyroidism, & patients with tumor hypercalcemia.

A circadian rhythm is present with highest plasma levels at 1400-1600 hours & lowest levels at 0800 hours.

Increases

• clinical disorders
  • primary hyperparathyroidism
  • secondary hyperparathyroidism
    • chronic renal disease (up to 10-fold increase)
  • pseudohypoparathyroidism
  • vitamin D deficiency
  • Zollinger-Ellison syndrome
  • spinal cord trauma
  • pseudogout
  • familial medullary thyroid carcinoma
  • multiple endocrine neoplasia (MEN) types I, IIa, IIb
  • both seizures
  • vasovagal syncope
• pharmaceutical agents:
  • in vivo effects
    • anticonvulsants, corticosteroids, isoniazid, lithium, phosphates, rifampin, fluoride

Decreases

• clinical disorders
  • autoimmune hypoparathyroidism
  • surgical hypoparathyroidism associated with thyroidectomy
  • sarcoidosis
  • non-parathyroid hypercalcemia in the absence of renal failure
  • hyperthyroidism
  • hypomagnesemia
  • transient neonatal hypocalcemia
  • DiGeorge syndrome
• pharmaceutical agents:
  • in vivo effects
    • cimetidine, pindolol, propranolol

Specimen

• The determination of PTH should be performed on serum. EDTA plasma has also been shown to be an acceptable sample. Collect blood sample in a red-top venipuncture tube & allow blood to clot. Centrifuge the sample & separate from cells. FREEZE SAMPLE IMMEDIATELY.
• Specimens showing particulate matter, erythrocytes, or turbidity should be centrifuged before testing.
• SAMPLE VOLUME: 400 uL of specimen is the minimum volume required to perform the assay.

More general terms

• parathyroid hormone intact in body fluid
• parathyroid hormone (parathyrin) in serum/plasma

Additional terms

• parathyroid hormone; parathormone; parathyrin (PTH)

Component of

• chronic kidney disease panel
• parathyroid panel

Patient information

parathyroid hormone (PTH), intact in serum patient information