What does an elevated intact Parathyroid Hormone (PTH) level indicate?

Elevated Intact PTH of 148 pg/mL Indicates Secondary Hyperparathyroidism

An intact parathyroid hormone (PTH) level of 148 pg/mL is significantly elevated above the normal range (typically 10-65 pg/mL) and most commonly indicates secondary hyperparathyroidism, likely due to chronic kidney disease (CKD). 1

Understanding PTH and Its Elevation

Parathyroid hormone is a critical regulator of calcium and phosphorus metabolism in the body. When intact PTH is elevated to 148 pg/mL, this suggests:

• Primary cause: Disruption in calcium-phosphorus homeostasis
• Most common etiology: Secondary hyperparathyroidism due to CKD
• Physiological response: The parathyroid glands are overproducing PTH in response to abnormal mineral metabolism

Differentiating Between Types of Hyperparathyroidism

Secondary Hyperparathyroidism (Most Likely)

• Occurs as a compensatory response to another condition
• Common in CKD patients due to:
  • Phosphate retention
  • Decreased vitamin D activation
  • Hypocalcemia
• PTH levels typically rise as kidney function declines 1

Primary Hyperparathyroidism (Less Likely)

• Characterized by autonomous PTH production
• Usually presents with hypercalcemia AND elevated PTH
• Caused by parathyroid adenoma, hyperplasia, or rarely carcinoma 2
• Would need calcium levels to confirm or rule out

Clinical Implications and Evaluation

When seeing a PTH of 148 pg/mL, the following should be assessed:

1. Kidney function: Measure GFR, creatinine, BUN
2. Mineral metabolism: Check serum calcium, phosphorus, and calcium-phosphorus product
3. Vitamin D status: Measure 25-hydroxyvitamin D levels
4. Bone health markers: Consider bone-specific alkaline phosphatase

Management Based on CKD Stage

The K/DOQI guidelines recommend different target ranges for intact PTH based on CKD stage 1:

• CKD Stage 3-4: Target PTH should be higher than normal range
• CKD Stage 5 (dialysis): Target PTH should be 150-300 pg/mL

Treatment Approaches

If secondary hyperparathyroidism is confirmed:

1. Phosphate control:

   • Dietary phosphate restriction
   • Phosphate binders to maintain phosphorus between 3.5-5.5 mg/dL in CKD Stage 5 1

2. Vitamin D therapy:

   • Calcitriol or vitamin D analogs (doxercalciferol, alfacalcidol, paricalcitol)
   • Dosing based on severity of hyperparathyroidism 1

3. Calcimimetics (for dialysis patients):

   • Cinacalcet can reduce PTH by increasing sensitivity of calcium-sensing receptors 3
   • Shown to reduce PTH by approximately 48-54% in clinical trials 3

4. Calcium supplementation:

   • If hypocalcemia is present and contributing to PTH elevation

Monitoring and Pitfalls

• Regular monitoring: Check PTH, calcium, and phosphorus every 1-3 months
• Avoid overcorrection: Suppressing PTH too much can lead to adynamic bone disease 1
• Watch for hypercalcemia: When using vitamin D analogs
• Assay limitations: Be aware that "intact PTH" assays may detect some biologically inactive fragments 1

Important Caveats

• PTH levels must be interpreted in context with calcium levels
• Normal PTH in the setting of hypercalcemia can still indicate primary hyperparathyroidism in rare cases 4
• Untreated hyperparathyroidism can lead to bone disease, vascular calcification, and increased cardiovascular mortality 1

If the PTH elevation is confirmed to be secondary to CKD, treatment should focus on addressing the underlying mineral metabolism disturbances while monitoring for complications of both the disease and its treatment.