Type of test Blood
Normal findings
Intact (whole): 10-65 pg/mL or 10-65 ng/L (SI units)
N terminal: 8-24 pg/mL
C terminal: 50-330 pg/mL
Test explanation and related physiology
This test is useful in establishing a diagnosis of hyperparathyroidism and distinguishing nonparathyroid from parathyroid causes of hypercalcemia. Increased PTH levels are seen in patients with hyperparathyroidism (primary, secondary, or tertiary); in patients with nonparathyroid, ectopic PTH-producing tumors (pseudohyperparathyroidism); or as a normal compensatory response to hypocalcemia in patients with malabsorption or vitamin D deficiency.
It is important to measure serum calcium simultaneous with the measurement of PTH. Most laboratories have a PTH/calcium nomogram already made up, indicating what PTH level is considered normal for each calcium level.
Decreased PTH levels are seen in patients with hypoparathyroidism or as a compensatory response to hypercalcemia in patients with metastatic bone tumors, sarcoidosis, vitamin D intoxication, or milk-alkali syndrome. Of course, surgical ablation of the parathyroids is another cause of hypoparathyroidism.
Interfering factors
* Drugs that increase PTH include anticonvulsants, isoniazid, lithium, rifampin, and steroids
* Drugs that decrease PTH include cimetidine and propranolol
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: yes
• Blood tube commonly used: red
• Obtain a morning blood specimen, because diurnal rhythm affects PTH levels. (Check with the laboratory if the patient works at night.)
• Note that some laboratories require blood in an iced plastic syringe.
• Obtain a serum calcium level determination at the same time if ordered. Serum PTH and serum calcium levels are important in the differential diagnosis.
• Indicate the time the blood was drawn on the laboratory slip because a diurnal rhythm affects test results.
Abnormal findings
Increased levels
- Hyperparathyroidism secondary to adenoma or carcinoma of the parathyroid gland
- Non–PTH-producing tumors (paraneoplastic syndrome)
- Lung carcinoma
- Kidney carcinoma
- Hypocalcemia
- Chronic renal failure
- Malabsorption syndrome
- Vitamin D deficiency
- Rickets
- Osteomalacia
- Congenital renal defect
Decreased levels
- Hypoparathyroidism
- Hypercalcemia
- Metastatic bone tumor
- Sarcoidosis
- Autoimmune destruction of the parathyroid glands
- Vitamin D intoxication
- Milk-alkali syndrome
- Graves disease
- Hypomagnesemia
- DiGeorge syndrome
