PTH, Intact and Ionized Calcium

Test Code: 36736

CPT Code(s): 82310, 82330, 83970

Includes: PTH Intact, Calcium, Ionized Calcium

Methodology: PTH Immunoassay (IA) • Calcium: Spectrophotometry (SP) • Ionized Calcium: Ion Specific Electrode (ISE)

Clinical Significance: The hormone Parathyroid Hormone (PTH) acts to increase serum calcium and 1-, 25- dihydroxyvitamin D concentrations, while decreasing phosphorus. Cross-reactivity with fragment 7-84 may occur in patients with renal insufficiency. The BioIntact PTH assay is considered the most reliable. Parathyroid function is related to the calcium concentration so both results should be interpreted together.

The assay is useful in making the diagnosis of primary hyperparathyroidism, secondary hyperparathyroidism, and a differential diagnosis of hypercalcemia. The assay helps in distinguishing hypercalcemia caused by either primary hyperparathyroidism or malignant disease.

Additional names: 3rd Generation PTH, Immunoreactive PTH, Intact Hormone, Parathyroid Hormone, PTH Whole Molecule, Sandwich PTH Assay, Two Site Antibody Assay, Intact PTH & CA, Monogram, Parathyroid, PTH, PTH Assay, PTH, Intact, PTH, Intact(Irma) & Calcium

Calcuim, Ionized

The Ionized Calcium is determined by an ion selective electrode methodology. The result that is generated is Ph adjusted. The result is empirically based on a measured Ph and Ionized Calcium concentration normalized to a Ph of 7.40. This calculation compensates for in-vitro changes in Ph due to loss of co2 through specimen handling. Ionized calcium represents the true "bioavailable" calcium in the circulation. In situations where the total calcium is normal but does not fit the clinical picture, e.g., Hyperpara-Thyroidism, a determination of the ionized calcium will, many times, show an elevation in the "bioavailable" calcium component. This may be due to alterations in protein concentrations, especially albumin, which binds most of the calcium in the circulation.