Normal Parathyroid Hormone (PTH) Levels
The normal range for intact parathyroid hormone (PTH) in individuals with normal kidney function is 10-65 pg/mL (7.15 pmol/L). 1
Understanding PTH Reference Ranges
- The normal PTH range of 10-65 pg/mL represents the standard reference range for individuals with normal kidney function 1, 2
- When vitamin D status is taken into account (excluding subjects with low 25OHD levels), a narrower reference range of 10-46 pg/mL may be more appropriate 2
- Most of the biological activity of PTH resides in the N-terminal portion, particularly in amino acid residues 1-7 1
- PTH is an 84-amino acid molecule, and most current assays measure the "intact" PTH molecule 1
Factors Affecting PTH Levels
- Vitamin D deficiency can lead to secondary hyperparathyroidism, as PTH levels rise to compensate for low vitamin D 1, 3
- Serum calcium levels directly affect PTH secretion through the calcium-sensing receptor (CaR) in the parathyroid gland 1
- Renal function significantly impacts PTH levels, with a moderate correlation between glomerular filtration rate and PTH (r = -0.36) 3
- PTH levels correlate weakly with 25-hydroxyvitamin D levels (r = -0.15) 3
Clinical Implications of Normal vs. Abnormal PTH
- PTH levels below normal (<10 pg/mL) may indicate hypoparathyroidism or vitamin D toxicity 2
- Elevated PTH (>65 pg/mL) in patients with normal kidney function may suggest:
- In primary hyperparathyroidism, approximately 12% of surgically confirmed cases may have PTH levels within the normal range (≤46 pg/mL) 2
Special Considerations for Chronic Kidney Disease
- In chronic kidney disease (CKD), PTH targets differ from the normal range due to skeletal resistance to PTH 5
- For patients with CKD Stage 5 on dialysis, intact PTH should be maintained between 150-300 pg/mL (2-4 times the upper limit of normal) 6, 5
- For CKD patients not on dialysis, PTH targets should progressively increase as kidney function declines 7, 6
- Maintaining PTH levels too low in CKD patients can lead to adynamic bone disease, while levels too high can cause osteitis fibrosa 5, 8
Measurement Considerations
- Many "intact PTH" assays also detect biologically inactive fragments (7-84 positions), which can lead to spurious elevations in CKD patients 1
- PTH measurements should be interpreted as trends rather than isolated values due to assay variability 6
- Different assays may have slightly different reference ranges, so laboratory-specific ranges should be considered 1
Clinical Pitfalls to Avoid
- Attempting to maintain intact PTH levels of CKD patients in the "normal" range (<65 pg/mL) can lead to low bone formation and adynamic bone disease 1, 5
- Relying solely on PTH without considering calcium, phosphorus, and vitamin D status can lead to suboptimal management 7, 6
- Failing to recognize that normal PTH levels do not exclude primary hyperparathyroidism, as up to 12% of confirmed cases may have PTH within normal range 4, 2
- Not accounting for vitamin D status when interpreting PTH levels can lead to misdiagnosis 1, 2