What does an elevated parathyroid hormone (PTH) of 134 pg/mL with normal serum calcium (9.3 mg/dL) and sufficient 25‑hydroxy‑vitamin D (43.4 ng/mL) indicate?

Normocalcemic Primary Hyperparathyroidism (NPHPT)

Your laboratory values—PTH 134 pg/mL with normal calcium (9.3 mg/dL) and sufficient vitamin D (43.4 ng/mL)—most likely represent normocalcemic primary hyperparathyroidism (NPHPT), a condition where autonomous parathyroid gland overactivity occurs despite normal serum calcium levels. 1

Understanding Your Results

Your specific values indicate:

• PTH is elevated at 134 pg/mL (normal range typically 15-65 pg/mL), representing approximately 2× the upper limit of normal 1
• Calcium is normal at 9.3 mg/dL (normal range 8.5-10.5 mg/dL) 2
• Vitamin D is sufficient at 43.4 ng/mL (target >30 ng/mL), effectively ruling out vitamin D deficiency as a cause of secondary hyperparathyroidism 1, 3

Critical Diagnostic Distinction

The key question is whether this represents normocalcemic primary hyperparathyroidism (autonomous parathyroid disease) versus secondary hyperparathyroidism (appropriate PTH response to an underlying problem). 3

Secondary Causes That MUST Be Excluded First

Before diagnosing NPHPT, the American College of Endocrinology requires ruling out all secondary causes: 1

• Inadequate calcium intake: Dietary calcium <1000-1200 mg/day can cause secondary hyperparathyroidism even with normal vitamin D 4, 3

  • A calcium challenge test (600 mg twice daily for 2-3 weeks) can confirm this—if PTH normalizes, the diagnosis was insufficient calcium intake 4
  • In one study, patients with mean PTH 80.6 pg/mL and calcium 9.2 mg/dL normalized completely with calcium supplementation alone 4

• Chronic kidney disease: Check estimated glomerular filtration rate (eGFR)—values <60 mL/min/1.73 m² indicate CKD-related secondary hyperparathyroidism 1, 3

• Medications: Thiazide diuretics, lithium, bisphosphonates, or denosumab can all elevate PTH 1, 3

• Malabsorption disorders: Celiac disease, inflammatory bowel disease, or bariatric surgery can impair calcium absorption 3

Clinical Significance of NPHPT

NPHPT is not a benign condition—despite normal calcium, it carries comparable risks to hypercalcemic primary hyperparathyroidism: 1

• Occult kidney stones and nephrocalcinosis occur in 26.5% of asymptomatic NPHPT patients 5

  • Patients with renal calcifications have significantly higher PTH (176 vs. 99 pg/mL), higher 1,25-dihydroxyvitamin D (97 vs. 62 pg/mL), and higher 24-hour urinary calcium (182 vs. 118 mg/day) 5
  • Your PTH of 134 pg/mL falls in the intermediate range, suggesting moderate risk

• Bone complications including osteoporosis and fractures 1

• Progressive disease: NPHPT can evolve into hypercalcemic primary hyperparathyroidism over time 3, 6

Recommended Diagnostic Workup

The Endocrine Society and American College of Endocrinology recommend the following algorithm: 1, 2

1. Confirm persistent elevation: Repeat serum calcium (albumin-corrected) and intact PTH simultaneously on at least 2-3 separate occasions 1, 3

2. Complete biochemical panel: 1, 2

   • Serum phosphate (typically low-normal in PHPT)
   • Serum creatinine and eGFR
   • 24-hour urine calcium, sodium, and creatinine
   • Ionized calcium if albumin is abnormal

3. Assess calcium intake: Obtain detailed dietary history—if intake is <1000 mg/day, perform a calcium challenge test (600 mg twice daily for 2-3 weeks, then recheck PTH) 4, 3

4. Medication review: Discontinue any medications that could elevate PTH if medically feasible 3

5. If NPHPT is confirmed, obtain: 1

   • Bone density scan (DXA) to assess for osteoporosis
   • Renal ultrasound to detect occult nephrocalcinosis or stones
   • Consider 24-hour urine calcium >400 mg/day as a surgical indication

Important Assay Considerations

PTH assays vary significantly between laboratories—differences of up to 47% exist between different assay generations, so always use assay-specific reference ranges and perform serial measurements in the same laboratory: 1, 2

• Second-generation "intact PTH" assays overestimate biologically active PTH by detecting inactive fragments 1
• Third-generation assays are more specific for full-length PTH 1
• Biotin supplements can interfere with PTH assays 1
• Blood should be collected in EDTA tubes and stored at 4°C for optimal stability 1, 2

Management Approach

If secondary causes are excluded and NPHPT is confirmed, referral to an endocrinologist and experienced parathyroid surgeon is appropriate: 1, 3

Surgical Indications in NPHPT

The Endocrine Society recognizes the following as indications for parathyroidectomy: 1

• Age <50 years
• Osteoporosis (T-score ≤-2.5 at any site)
• eGFR <60 mL/min/1.73 m²
• 24-hour urine calcium >400 mg/day
• Kidney stones or nephrocalcinosis
• Patient preference for definitive treatment 1

Medical Management for Non-Surgical Candidates

If surgery is declined or contraindicated: 1

• Maintain 25-hydroxyvitamin D >20 ng/mL (yours is already optimal at 43.4 ng/mL)
• Ensure adequate dietary calcium intake (1000-1200 mg/day), but avoid excessive supplementation
• Monitor serum calcium every 3 months
• Repeat bone density scan every 1-2 years
• Avoid dehydration and thiazide diuretics

Common Pitfalls to Avoid

• Not assessing dietary calcium intake before diagnosing NPHPT—this is a reversible cause that resolves with simple supplementation 1, 4
• Ordering parathyroid imaging before biochemical confirmation—imaging is for surgical planning only, not diagnosis 2
• Using different PTH assays for serial monitoring—this creates artificial variability 1
• Assuming normal calcium means no disease—NPHPT carries real risks for kidney stones and bone loss 1, 5

Next Steps

1. Immediate: Assess your daily dietary calcium intake—if <1000 mg/day, consider a 2-3 week trial of calcium supplementation (600 mg twice daily) with repeat PTH measurement 4

2. Within 2-4 weeks: Repeat albumin-corrected serum calcium and intact PTH (same laboratory) to confirm persistence 1, 3

3. If PTH remains elevated: Complete the full diagnostic workup including 24-hour urine collection, renal ultrasound, and bone density scan 1

4. Referral: Consult an endocrinologist for definitive diagnosis and management planning 1, 3