Normal Parathyroid Hormone (PTH) Levels
The normal range for intact PTH is below 65 pg/mL (7.15 pmol/L) in individuals with normal kidney function. 1
Understanding PTH Reference Ranges
PTH is an 84-amino acid peptide hormone that plays a crucial role in calcium homeostasis. When interpreting PTH levels, several important considerations must be kept in mind:
Normal PTH Range in Different Populations
- Individuals with normal kidney function: Below 65 pg/mL (7.15 pmol/L)
- CKD patients (Stages 3-4): Target range differs from normal range
- Dialysis patients: Higher target ranges are recommended (120-180 pg/mL or 2-3 times the upper normal limit) 2
Factors Affecting PTH Measurement
PTH measurement can vary significantly based on several factors:
- Assay type: Different second-generation assays can produce varying results 3
- Sample type: Serum samples generally yield different results than EDTA plasma or citrate plasma 3
- Laboratory methodology: Each laboratory should establish its own reference ranges 1
Clinical Implications of PTH Levels
Abnormally Low PTH
- PTH levels below normal range in CKD patients may indicate adynamic bone disease
- When intact PTH levels fall below 65 pg/mL in CKD patients, adynamic bone is nearly universal 1
- Adynamic bone disease is associated with increased risk of hypercalcemia and potentially vascular calcification 1
Abnormally High PTH
- Elevated PTH with hypercalcemia typically indicates primary hyperparathyroidism
- In CKD patients, secondary hyperparathyroidism develops as kidney function declines
- High PTH levels in pediatric dialysis patients (>500 pg/mL) have been associated with impaired growth, cardiovascular complications, and increased mortality 2
Important Considerations for PTH Interpretation
- Assay variability: Many "intact PTH" assays also detect biologically inactive fragments (7-84 positions), leading to spurious elevations in CKD patients 1
- Sample handling: For optimal interpretation, standardized blood handling is recommended; serum PTH is preferred over EDTA or citrate plasma 3
- Clinical context: PTH must be interpreted alongside calcium, phosphate, and vitamin D levels
- Normal PTH with hypercalcemia: In primary hyperparathyroidism, PTH may be within the normal range but inappropriately normal for the elevated calcium level 4, 5
Pitfalls in PTH Interpretation
- Laboratory variation: Different laboratories may have different reference ranges
- Assay differences: Up to 11 of 34 patients in one study were classified in different treatment categories when using different assays 3
- Sample type differences: Up to 7 of 34 patients were classified differently based on blood specimen type 3
- Post-surgical monitoring: After parathyroidectomy, elevated PTH with normal calcium may occur in about 18% of patients 6
When interpreting PTH values, always consider the clinical context, kidney function, calcium levels, and the specific assay used by your laboratory. The combination of these factors will provide the most accurate assessment of parathyroid function and guide appropriate clinical decision-making.