Parathyroid Hormone Interpretation

Primary Causes of Elevated PTH

Primary Hyperparathyroidism (PHPT) is characterized by autonomous overproduction of PTH from abnormal parathyroid tissue, leading to hypercalcemia with elevated or inappropriately normal PTH, according to the Endocrine Society 2
Normocalcemic variant of Primary Hyperparathyroidism has elevated PTH with normal calcium levels, still at risk for complications of classic PHPT, as stated by the Endocrine Society 1
Secondary Hyperparathyroidism (SHPT) is a compensatory increase in PTH due to vitamin D deficiency, the most common cause, or chronic kidney disease (CKD), which disturbs calcium and phosphate homeostasis, as reported by the Endocrine Society 1, 2, 3
Tertiary Hyperparathyroidism occurs when hyperplastic parathyroid glands become autonomous after longstanding secondary hyperparathyroidism, often in patients after kidney transplantation, according to the American Society of Nephrology 4

PTH levels are higher in Black individuals compared to White individuals, and increase with age due to declining kidney function, as stated by the Endocrine Society 1, 2
Higher PTH concentrations are found in obese patients, and vitamin D deficiency increases PTH levels, as reported by the Endocrine Society 1, 2
PTH is more stable in EDTA plasma than serum, and sampling site and time can affect PTH concentrations, with a circadian rhythm, as stated by the Endocrine Society 1

Calcium levels should always be measured alongside PTH, with elevated calcium and elevated PTH suggesting primary hyperparathyroidism, according to the Endocrine Society 2
Normal calcium and elevated PTH may indicate normocalcemic PHPT, vitamin D deficiency, or early CKD, as reported by the Endocrine Society 1, 2
Different PTH assay generations may yield different results, and assay-specific reference values should be used when interpreting results, as stated by the Endocrine Society 1, 2
Biotin supplements can interfere with some PTH assays, according to the Endocrine Society 1, 2

Vitamin D levels (25-OH vitamin D) should be considered, as stated by the American Society of Nephrology 5
Kidney function tests (creatinine, GFR) and phosphorus levels should be evaluated, as reported by the Endocrine Society and the American Society of Nephrology 3, 5

Failure to consider vitamin D status can lead to misdiagnosis, as stated by the Endocrine Society 1, 2
Not accounting for biological variation, with PTH having substantial biological variation, can affect interpretation, according to the Endocrine Society 2
Ignoring kidney function can lead to elevated PTH, even with mild reductions in GFR, as reported by the American Society of Nephrology 5
Using inappropriate reference ranges, which should account for vitamin D status, BMI, race, age, and the specific assay used, can affect interpretation, as stated by the Endocrine Society 1, 2