Parathyroid Hormone

This is a test to determine whether PTH levels are responding normally to changes in blood calcium levels. It also helps to distinguish the cause of calcium imbalances, and to evaluate parathyroid function. When calcium blood levels are higher or lower than normal, and when your caregiver may want to determine how well your parathyroid glands are working.

Parathyroid hormone (PTH) helps the body maintain stable levels of calcium in the blood. It is part of a 'feedback loop' that includes calcium, PTH, vitamin D, and, to some extent, phosphate and magnesium. Conditions and diseases that disrupt this feedback loop can cause inappropriate elevations or decreases in calcium and PTH levels and lead to symptoms of hypercalcemia (raised blood levels of calcium) or hypocalcemia (low blood levels of calcium).

PTH is produced by four parathyroid glands that are located in the neck beside the thyroid gland. Normally, these glands secrete PTH into the bloodstream in response to low blood calcium levels. Parathyroid hormone then works in three ways to help raise blood calcium levels back to normal. It takes calcium from the body's bone, stimulates the activation of vitamin D in the kidney (which in turn increases the absorption of calcium from the intestines), and suppresses the excretion of calcium in the urine (while encouraging excretion of phosphate). As calcium levels begin to increase in the blood, PTH normally decreases.

PREPARATION FOR TEST

You should have nothing to eat or drink except for water after midnight on the day of the test or as directed by your caregiver. A blood sample is obtained by inserting a needle into a vein in the arm.

NORMAL FINDINGS

Conventional Normal

  • PTH intact (whole)

  • Assay includes intact PTH

  • Values (pg/mL)10-65

  • SI Units (ng/L)10-65

  • PTH N-terminalN-terminal 

  • Values (pg/mL) 8-24

  • SI Units (ng/L) 8-24

  • PTH C-terminal

  • Assay Includes C-terminal

  • Values (pg/mL) 50-330

  • SI Units (ng/L) 50-330

  • Intact PTH

  • Midmolecule

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.

MEANING OF TEST

Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.