Normal Parathyroid Hormone Levels
In individuals with normal kidney function, the normal range for intact parathyroid hormone (PTH) is approximately 12-88 pg/mL, though the specific reference range varies by laboratory and assay method used. 1
Standard Reference Ranges
The typical normal range for intact PTH in healthy adults is below 65 pg/mL (7.15 pmol/L) according to K/DOQI guidelines, though individual laboratories may report slightly different ranges. 2
One commonly cited reference range is 2.0 to 6.8 pmol/L (approximately 18-63 pg/mL when converted), based on measurements in healthy subjects. 3
Another frequently used clinical range is 12.0-88.0 pg/mL, which represents the upper limit used in many hospital laboratories. 1
Critical Context: PTH Must Be Interpreted With Calcium
PTH levels cannot be interpreted in isolation—they must always be evaluated in relation to serum calcium levels. 4, 5
In normal individuals, there is a significant inverse relationship between serum calcium and PTH levels: as calcium rises, PTH appropriately suppresses. 5
A PTH level that appears "normal" by laboratory reference range may actually be inappropriately elevated if the patient is hypercalcemic, indicating primary hyperparathyroidism. 4, 6
Approximately 7% of patients with primary hyperparathyroidism have PTH values within the normal reference range, but these values are inappropriate given their elevated calcium levels. 6
Assay-Specific Considerations
The generation and type of PTH assay used significantly affects the measured value, making it essential to know which assay your laboratory uses. 7
Second-generation "intact PTH" assays measure both full-length PTH (1-84) and inactive fragments (particularly 7-84 PTH), leading to overestimation of biologically active hormone. 7
Third-generation assays are more specific, measuring only full-length 1-84 PTH by using antibodies against the first four amino acids, and can yield values that differ by up to 47% from second-generation assays. 7
Sequential measurements should always be performed with the same assay in the same laboratory to ensure accurate trend evaluation. 7
Special Populations: Chronic Kidney Disease
Normal PTH ranges do NOT apply to patients with chronic kidney disease—attempting to maintain "normal" PTH levels in CKD patients can cause adynamic bone disease. 2, 7
PTH levels begin to rise when GFR falls below 60 mL/min/1.73 m², representing an appropriate compensatory response. 2, 7
In CKD Stage 3, the target intact PTH is 35-70 pg/mL, not the normal range. 7
In CKD Stage 4, the target intact PTH is 70-110 pg/mL. 7
In CKD Stage 5 (dialysis), the target intact PTH is 150-300 pg/mL. 7
Common Pitfalls to Avoid
Never interpret PTH without simultaneously checking serum calcium—this is the most common diagnostic error. 4, 5
Do not assume a PTH value within the laboratory reference range excludes hyperparathyroidism if calcium is elevated. 4, 6
Be aware that vitamin D deficiency can cause secondary elevation of PTH even with normal calcium, which is a different entity than primary hyperparathyroidism. 7
Recognize that patients with hypercalcemia and PTH ≤50 pg/mL still have primary hyperparathyroidism (58.9% have multiglandular disease) and should be considered for parathyroidectomy. 1