At what Parathyroid Hormone (PTH) level should I be concerned about hyperparathyroidism?

PTH Levels Requiring Concern for Hyperparathyroidism

For patients with chronic kidney disease (CKD), concern for hyperparathyroidism should begin when PTH levels are persistently above the upper normal limit for the assay, with specific target ranges varying by CKD stage. 1

PTH Targets by Patient Population

Non-CKD Patients

• Primary hyperparathyroidism should be suspected when:
  • PTH is elevated or inappropriately normal in the presence of hypercalcemia
  • Even normal PTH levels with hypercalcemia can represent primary hyperparathyroidism 2, 3

CKD Patients (Not on Dialysis)

• For CKD G3a-G5 not on dialysis:
  • Evaluate for modifiable factors when PTH is persistently above the upper normal limit or progressively rising 1
  • Modifiable factors include: hyperphosphatemia, hypocalcemia, high phosphate intake, and vitamin D deficiency

Dialysis Patients

• For CKD G5D (on dialysis):
  • Target PTH range: approximately 2-9 times the upper normal limit for the assay 1
  • Marked changes in either direction within this range should prompt therapy adjustment

Factors Affecting PTH Interpretation

Several factors influence PTH levels and must be considered when interpreting results:

• Race: PTH is higher in Black compared to White individuals 1
• Age: PTH increases with age (partly due to declining GFR) 1
• BMI: Higher PTH levels are seen in obese patients 1
• Vitamin D status: Vitamin D deficiency increases PTH (secondary hyperparathyroidism) 1
• Assay variability: Different PTH assays may yield different results; use assay-specific reference ranges 1
• Sample type: PTH is more stable in EDTA plasma than serum 1

When to Consider Intervention

For Primary Hyperparathyroidism

• Parathyroidectomy is indicated for:
  • Symptomatic patients
  • Patients with osteoporosis
  • Impaired kidney function (GFR < 60 mL/min/1.73 m²)
  • Kidney stones or hypercalciuria
  • Patients ≥ 50 years of age
  • Calcium increased >0.25 mmol/L above upper limit of normal 1

For Secondary Hyperparathyroidism in CKD

• Severe hyperparathyroidism (PTH >800 pg/mL) with hypercalcemia refractory to medical therapy may require parathyroidectomy 4
• For CKD G5D patients requiring PTH-lowering therapy, options include:
  • Calcimimetics (cinacalcet)
  • Calcitriol
  • Vitamin D analogs
  • Combination therapy 1

Special Considerations

• Normocalcemic hyperparathyroidism: Elevated PTH with normal calcium levels requires careful evaluation to distinguish between normocalcemic primary hyperparathyroidism and secondary causes 5
• Biological variation: PTH has substantial within-subject variation (~20% in healthy people, up to 30% in hemodialysis patients) 1
• Rare presentations: Primary hyperparathyroidism can occasionally present with normal or even undetectable PTH levels 6, 3

Monitoring Recommendations

• Post-transplant patients: Measure calcium and phosphate at least weekly until stable 1
• CKD patients: Monitoring frequency should be based on CKD stage and presence/magnitude of abnormalities 1

Remember that PTH levels should always be interpreted in the context of calcium, phosphate, and vitamin D status, as these parameters are interrelated in mineral bone disorders.