From the Guidelines
Testing for parathyroid imbalance primarily involves measuring blood calcium and parathyroid hormone (PTH) levels, with serum calcium as the initial screening test, followed by intact PTH measurement if abnormal, as recommended by the most recent guidelines 1.
Key Tests for Parathyroid Imbalance
- Serum calcium: The first step in screening for parathyroid imbalance, with abnormal results prompting further investigation with intact PTH measurement.
- Intact PTH measurement: Crucial for diagnosing primary hyperparathyroidism, where PTH levels are elevated despite high calcium levels.
- Comprehensive panel: Including calcium, PTH, phosphorus, vitamin D (25-hydroxyvitamin D), and kidney function tests (BUN, creatinine) for suspected hyperparathyroidism.
- Ionized calcium: Provides the most accurate assessment of calcium status.
- 24-hour urine calcium collection: Helps distinguish between different forms of hyperparathyroidism.
- Magnesium levels: Should be checked in cases of suspected hypoparathyroidism, as deficiency can mimic the condition.
Imaging and Additional Tests
- Imaging studies (ultrasound, sestamibi scan, or 4D-CT): May be necessary to localize abnormal parathyroid glands if surgery is considered.
- Bone density testing: Often warranted to assess for osteoporosis in hyperparathyroidism.
Interpretation of Test Results
- The inverse relationship between calcium and PTH is key to interpretation: high calcium with high PTH suggests primary hyperparathyroidism, while low calcium with low PTH indicates hypoparathyroidism, as noted in recent clinical guidelines 1.
Clinical Considerations
- The choice of PTH assay can impact clinical decisions, particularly in cases of secondary hyperparathyroidism or during parathyroid surgery, highlighting the need for awareness of assay differences 1.
- Recent international guidelines emphasize the importance of preoperative imaging in the reoperative setting to localize target parathyroid lesions and identify postoperative changes from previous parathyroid explorations 1.
From the FDA Drug Label
At study entry, 66% of the patients were receiving vitamin D sterols and 93% were receiving phosphate binders. Cinacalcet (or placebo) was initiated at a dose of 30 mg once daily and titrated every 3 or 4 weeks to a maximum dose of 180 mg once daily to achieve an iPTH of ≤ 250 pg/mL Plasma iPTH levels were measured using the Nichols IRMA.
The testing for parathyroid imbalance involves measuring iPTH (intact parathyroid hormone) levels, with a target of ≤ 250 pg/mL.
- iPTH is measured using the Nichols IRMA assay.
- The goal is to achieve an iPTH level of ≤ 250 pg/mL. 2
From the Research
Testing for Parathyroid Imbalance
To test for parathyroid imbalance, it is essential to understand the role of parathyroid hormone (PTH) in regulating extracellular calcium and phosphate levels 3. PTH enhances calcium reabsorption, increases the synthesis of 1,25-dihydroxyvitamin D, and increases bone resorption to maintain calcium homeostasis.
Diagnostic Approaches
The accurate assessment of PTH provides essential biochemical information to diagnose parathyroid disease 3. However, currently available immunoassays may overestimate or underestimate bioactive PTH due to interferences from truncated PTH fragments, phosphorylation of PTH, and oxidation of amino acids of PTH. Some key points to consider in testing for parathyroid imbalance include:
- Measuring PTH levels to diagnose hyperparathyroidism, which can be primary, secondary, or tertiary 4
- Assessing calcium levels, as hypercalcemia can be a feature of primary hyperparathyroidism (PHP) 4
- Evaluating renal function, as kidney failure can induce secondary hyperparathyroidism (SHP) 4
- Considering the use of calcium loading tests to diagnose normocalcemic PHP 4
Biochemical Markers
Biochemical markers, such as PTH, calcium, and phosphate levels, play a crucial role in diagnosing parathyroid disease. Some key markers include: