Do I need an intact Parathyroid Hormone (PTH) blood test?

Intact PTH Blood Test: When It's Needed

You need an intact PTH blood test if you have chronic kidney disease (CKD) with GFR <60 mL/min/1.73 m², or if you have symptoms or risk factors for parathyroid disorders. 1, 2

Indications for Intact PTH Testing

Chronic Kidney Disease

• Required for all patients with CKD stage 3-5 (GFR <60 mL/min/1.73 m²) 1
• Testing frequency based on CKD stage:
  • Stage 3 (GFR 30-59): Test every 12 months
  • Stage 4 (GFR 15-29): Test every 3 months
  • Stage 5 (GFR <15 or dialysis): Test every 3 months 1
• More frequent testing needed when:
  • Receiving treatment for calcium/phosphorus abnormalities
  • Starting vitamin D therapy
  • After kidney transplantation 1, 2

Other Clinical Indications

• Suspected primary hyperparathyroidism
• Evaluation of hypercalcemia or hypocalcemia
• After bariatric surgery (risk of calcium/vitamin D malabsorption) 1
• After thyroid surgery (to detect hypoparathyroidism) 1
• Monitoring during parathyroidectomy 1
• Bone disorders or unexplained bone pain 1
• Unexplained fractures with minimal trauma 1

Interpretation and Clinical Significance

• PTH results must be interpreted alongside:

  • Serum calcium
  • Serum phosphorus
  • Alkaline phosphatase (bone turnover marker)
  • Vitamin D status 2

• Target PTH ranges vary by CKD stage:

  • Higher targets for advanced CKD due to PTH resistance
  • Both high and low PTH levels correlate with increased mortality in dialysis patients 2, 3

• In CKD patients, intact PTH helps:

  • Distinguish between high-turnover and low-turnover bone disease
  • Guide treatment decisions for secondary hyperparathyroidism
  • Monitor response to therapy with vitamin D analogs, phosphate binders, and calcimimetics 2

Important Considerations

Test Accuracy

• Intact PTH assay (second-generation) is superior to older assays 2, 4
• Different intact PTH assays can vary up to 47% in results 2
• Sequential measurements should use the same assay for proper trend analysis 1, 2

Common Pitfalls

• Interpreting PTH in isolation without considering calcium, phosphorus, and vitamin D status 2
• Comparing results from different assay generations or manufacturers 2
• Failing to recognize that intact PTH assays measure both active and inactive fragments 2
• Targeting normal PTH ranges in CKD patients (can lead to adynamic bone disease) 2

Clinical Impact

• Only about 12.8% of dialysis patients have all mineral metabolism markers within target ranges, highlighting the need for individualized monitoring 3
• Both high and low PTH levels are associated with cardiovascular complications 5
• PTH is considered a uremic toxin in advanced CKD, contributing to bone disease, soft tissue calcification, and other systemic complications 6

The intact PTH test is a crucial tool for managing mineral metabolism disorders, especially in CKD patients, where it guides treatment decisions that impact bone health, cardiovascular risk, and overall mortality.