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PTH, Intact and Calcium

Test code(s) 8837

Question 1. What is the purpose of this test?

This test is used to:

  • Diagnose and monitor hypo- and hyperparathyroidism
  • Differentiate primary hyperparathyroidism from hypercalcemia of malignancy

Intact PTH is the biologically active form of parathyroid hormone. It acts to increase circulating calcium, decrease circulating phosphorous, and increase the active form of vitamin D [1,25(OH)2D], by mobilizing calcium from bone and retaining calcium in the kidneys.

Question 2. How are test results interpreted?

Results observed in various conditions follow1:

  • Primary hyperparathyroidism: elevated PTH and calcium
  • Hypercalcemia of malignancy: PTH within or below the reference range and elevated calcium
  • Renal failure: elevated PTH and decreased calcium
  • Secondary hyperparathyroidism: elevated PTH and decreased calcium
  • Hypoparathyroidism: decreased PTH and calcium

Question 3. Is there any patient preparation required for this test?

No patient preparation is required.

Question 4. What type of specimen is required?

The preferred specimen is frozen serum.      

Question 5. What can interfere with PTH measurements?

Heterophile antibodies (antibodies to animal immunoglobulins) present in the patient’s blood could cause anomalous results.

Question 6. How can I compare results obtained using different methods?

PTH values vary from one method to the next. You can compare values generated by different methods by comparing where each result falls within the respective method’s reference interval. Calcium values may vary among methods as well and can be compared in the same manner.

Question 7. Where can I go for more information about PTH measurements?

The following reference may be helpful:

Broussard JH, Lepage R, Cardinal H, et al. Influence of glomerular filtration on non-(1-84) parathyroid hormone (PTH) detected by intact PTH assays. Clin Chem. 2000;46:697-703.

 

References

  1. Kaplan LA,  Pesce AJ, eds. Clinical Chemistry : Theory, Analysis, Correlation.  St. Louis, MO: Mosby Elsevier;2010: 638-643.
This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
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