Patient with known hypercalcemia has serum calcium 11.7 mg/dL and intact parathyroid hormone 84 pg/mL—how should I explain these findings in simple terms to a new nurse practitioner?

Understanding Elevated PTH and Calcium in Primary Hyperparathyroidism

These lab results show primary hyperparathyroidism: the parathyroid glands are autonomously secreting too much PTH despite the elevated calcium, when they should be "shut off" by the high calcium level. 1

What the Numbers Mean

Normal vs. This Patient:

• Normal calcium: 8.6–10.3 mg/dL 1
• This patient's calcium: 11.7 mg/dL (clearly elevated) 1
• Normal PTH: varies by assay, typically 10–65 pg/mL 1
• This patient's PTH: 84 pg/mL (elevated or inappropriately normal) 1

The key concept: In a healthy person, when calcium rises above 10.3 mg/dL, the parathyroid glands should completely shut down and PTH should drop to near zero. 1 Instead, this patient's PTH is 84 pg/mL—it's either elevated or "inappropriately normal" for someone with hypercalcemia. 1 This mismatch confirms the parathyroid glands are malfunctioning and secreting PTH autonomously, regardless of the calcium level. 1

Simple Explanation for the New NP

Think of it like a broken thermostat:

• The parathyroid glands normally act like a thermostat that senses calcium levels 1
• When calcium gets too high, they should turn "off" and stop making PTH 1
• In primary hyperparathyroidism, the thermostat is broken—it keeps producing PTH even when calcium is already too high 1
• The elevated PTH then pulls even more calcium from the bones and increases calcium absorption from the gut, creating a vicious cycle 1

Why Both Values Matter

PTH of 84 pg/mL with calcium of 11.7 mg/dL confirms primary hyperparathyroidism because: 1

• The PTH should be suppressed (near zero) when calcium is this high 1
• Any detectable PTH in the setting of hypercalcemia is "inappropriate" and diagnostic 1
• This pattern (elevated calcium + elevated or normal PTH) distinguishes primary hyperparathyroidism from other causes of high calcium like cancer or vitamin D toxicity, where PTH would be suppressed 1

Clinical Significance

This calcium level (11.7 mg/dL) represents moderate hypercalcemia and requires action: 1, 2

• Calcium >1 mg/dL above the upper limit of normal (>11.3 mg/dL) is a surgical indication 1
• Patients may experience polyuria, polydipsia, nausea, confusion, and muscle weakness 1
• The elevated PTH is actively pulling calcium from bones, which can lead to osteoporosis and fractures 1
• Hypercalcemia can cause kidney stones and impair kidney function over time 1

Next Steps for This Patient

Immediate actions: 1

• Measure 25-hydroxyvitamin D to exclude vitamin D deficiency as a secondary cause of PTH elevation 1
• Check serum creatinine and eGFR to assess kidney function 1
• Obtain 24-hour urine calcium or spot urine calcium/creatinine ratio 1
• Consider bone density scan if chronic hyperparathyroidism is suspected 1

Definitive management: 3

• Refer to endocrinology for confirmation and medical optimization 3
• Refer to an experienced, high-volume parathyroid surgeon for evaluation 3
• Parathyroidectomy is the only definitive cure and is indicated when calcium exceeds 11.3 mg/dL 1, 3

Common Pitfalls to Avoid

Do not assume PTH must be "very high" to diagnose primary hyperparathyroidism: 1

• Even a PTH in the "normal range" (like 84 pg/mL) is diagnostic when calcium is elevated 1
• The key is that PTH is not suppressed as it should be 1

Do not delay surgical referral while attempting medical management: 1

• This calcium level (11.7 mg/dL) meets surgical criteria 1
• Medical management alone does not cure the disease 3

Do not order parathyroid imaging before confirming the biochemical diagnosis: 1

• Imaging is for surgical planning, not diagnosis 1
• The diagnosis is made by labs alone: elevated calcium + elevated or inappropriately normal PTH 1