Investigations
1st investigations to order
serum calcium
Test
First-line test for diagnosis. Highly sensitive and specific. Normal limits can vary between laboratories. Blood sample should be taken at same time as sample for intact parathyroid hormone (iPTH) is taken. Either total or ionised calcium levels may be used, but the same test should be used consistently over time to allow proper comparison and trend analysis.
Total serum calcium levels should be corrected for serum albumin. An ionised calcium level is preferred.
Result
<2.10 mmol/L (<8.4 mg/dL)
serum intact parathyroid hormone (iPTH)
Test
First-line and definitive test for diagnosis of hyperparathyroidism. Older assays using parathyroid hormone (PTH) fragments are less reliable and have been abandoned for the intact assay. iPTH should always be ordered with a paired calcium level so that the PTH level can be properly interpreted. Value varies with reference laboratory used.
Result
>88 nanograms/L (>88 picograms/mL)
serum creatinine
Test
Used to establish renal function, in combination with urea. Estimated glomerular filtration rate (GFR) values are calculated using the isotope dilution mass spectrometry (IDMS)-traceable modification of diet in renal disease (MDRD) equation.[38]
GFR values of up to 59 mL/minute/1.73 m² may be associated with chronic kidney disease (CKD).
Result
>91.5 micromol/L (>1.2 mg/dL) in CKD
serum urea
Test
In combination with serum creatinine, it establishes renal function. Estimated GFR values are calculated using the isotope dilution mass spectrometry (IDMS)-traceable modification of diet in renal disease (MDRD) equation.[38]
Result
>7.14mmol/L (>20 mg/dL) in chronic kidney disease
Investigations to consider
serum phosphorus
Test
Allows appreciation of the severity of kidney disease. May indicate the need for phosphorus reduction therapy.
When phosphorus level is elevated in addition to elevated serum creatinine and urea, this points to chronic kidney disease (CKD) as the aetiology of SHPT. If phosphorus levels are low, other anomalies such as vitamin D deficiency are more likely.[9]
High calcium and phosphorus levels may be a risk for calciphylaxis, a lethal, small-, and mid-size arteriolar vasculopathy.
Result
variable; >1.45 mmol/L (>4.5 mg/dL) in CKD
serum 25-hydroxyvitamin D
Test
Deficiency may be the principal cause of SHPT or the consequence of another underlying condition, and will need correction by replenishment.
Result
<40 to 75 nanomol/L (<16 to 30 nanograms/mL) if inadequate vitamin D (varies on reference lab)
serum magnesium
ultrasound neck
Test
Used to confirm parathyroid gland disease. Provides an estimate of parathyroid gland size and location, and might be used as a surgical road map for resection.
Result
parathyroid gland hyperplasia
99Tc-sestamibi (MIBI) scan
Test
Used to confirm parathyroid gland disease. Provides an estimate of parathyroid gland size and location, and might be used as a surgical road map for resection (can allow for intra-operative radioguided parathyroid gland surgery).[41]
One meta-analysis has, however, found that planar parathyroid scintigraphy using 99Tc-MIBI did not provide adequate diagnostic accuracy in patients with SHPT and diffuse or nodular hyperplasia, and therefore should not be used as a first-line diagnostic imaging method in the presurgical detection of parathyroid gland hyperplasia.[43]
99mTc-MIBI single-photon emission computed tomography (SPECT)/CT has shown better sensitivity than 99mTc-MIBI planar scintigraphy in identifying parathyroid lesion in SHPT. 99mTc-MIBI SPECT/CT sensitivity is further improved when used in combination with ultrasound.[44]
Result
parathyroid gland hyperplasia
high-resolution contrast CT scan neck and upper chest
Test
Allows for visualisation of parathyroid tissue based on the pattern of tissue enhancement, following the administration of iodinated intravenous contrast medium. The upper chest is included in the imaging to look for possible ectopic or supernumerary parathyroid glands.
Result
parathyroid gland hyperplasia
MRI neck and upper chest
Test
May be used to confirm parathyroid gland disease. Provides an estimate of parathyroid gland size and location, and might be used as a surgical road map for resection. The upper chest is included in the imaging to look for possible ectopic or supernumerary parathyroid glands.
Result
parathyroid gland hyperplasia
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