Parathyroid hormone measurement is used in the diagnosis and differential diagnosis of hypercalcemia, in the diagnosis of primary, secondary, and tertiary hyperparathyroidism, in the diagnosis of hypoparathyroidism, and in the monitoring of patients with end-stage renal failure for possible renal osteodystrophy.
Parathyroid hormone (PTH) is determined using highly sensitive immunological methods to detect and measure several molecular forms of parathyroid hormone: the entire molecule (intact) and its various fragments. Either the N-terminal (amino-terminal) fragments or the C-terminal (carboxy-terminal) fragments of the parathyroid hormone may be measured.
The intact parathyroid hormone is secreted by the parathyroid glands and metabolized by the liver and kidneys into N-terminal and C-terminal fragments. The intact molecule and N-terminal fragments are useful for identifying potential acute conditions, whereas the C-terminal fragments indicate chronic abnormalities of PTH metabolism.
Parathyroid hormone is directly responsible for regulating plasma calcium and phosphorus. When the body's self-regulatory mechanism perceives a decrease in calcium levels in the blood serum, the parathyroid glands are stimulated to secrete parathyroid hormone. Increased serum parathyroid hormone causes calcium to be released from the bones and stimulates the renal tubules to increase calcium ion uptake in the distal tubes and reduce phosphorus uptake in the proximal tubules. When the serum calcium concentration becomes sufficient again, the parathyroid glands decrease the secretion of parathyroid hormone.
When there is a primary tumor or hyperplasia of the parathyroid glands, the mechanism of self-regulation of the calcium-parathyroid hormone fails. As the secretion of parathyroid hormone increases, so does serum calcium levels, eventually leading to a hypercalcemic condition that can be life-threatening.
Measuring parathyroid hormone is useful in differentiating the causes of hypercalcemia, those due to parathyroid glands, and that from causes other than parathyroid glands. The other causes of hypercalcemia generally appear with normal, slightly high, or even low levels of hormones. Thus, parathyroid hormone should always be evaluated in conjunction with ionized calcium levels.
Parathyroid hormone testing is primarily used in the evaluation of pathological conditions of calcium (hypercalcemia & hypocalcemia) and to help diagnose hyperparathyroidism or hypoparathyroidism. Ionized calcium is also commonly measured at the same time. Parathyroid hormone is also controlled in patients with chronic kidney disease.
Possible Interpretations of Pathological Values
- Increase: In response to low serum calcium levels caused by malabsorption, chronic kidney failure, dietary vitamin D deficiency, osteomalacia, and renal dialysis. Also ectopic PTH production, lactation, primary hyperparathyroidism, parathyroid adenoma, parathyroid carcinoma, parathyroid hyperplasia, pregnancy, pseudohypoparathyroidism (sometimes), renal hypercalciuria, rickets (vitamin D-dependent, vitamin D deficiency), secondary hyperparathyroidism, squamous cell carcinoma (kidney, lung, ovary, pancreas). Parathyroid hormone levels increase with age
- Decrease: In response to high levels of calcium, autoimmune disease, cancer, Graves' disease, hypomagnesemia, hypoparathyroidism, parathyroidectomy (transient decrease), sarcoidosis, vitamin A and D poisoning. Medications: Thiazide diuretics. False low parathyroid hormone levels were observed after drinking milk prior to testing
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.