What is the appropriate workup for a patient with hypercalcemia?

Hypercalcemia Workup

The initial workup of hypercalcemia requires measurement of serum PTH to distinguish PTH-dependent from PTH-independent causes—this single test directs all subsequent diagnostic steps. 1

Initial Laboratory Assessment

Measure the following immediately:

• Serum calcium (total and ionized if available)
• Serum PTH (intact parathyroid hormone)
• Serum phosphate
• Serum creatinine
• 24-hour urine calcium

The PTH level is the critical branch point that determines your entire diagnostic pathway 2, 1.

Diagnostic Algorithm Based on PTH

PTH Elevated or Inappropriately Normal (PTH ≥20 pg/mL)

This indicates PTH-dependent hypercalcemia:

• Primary hyperparathyroidism is the most likely diagnosis
• Obtain parathyroid imaging (sestamibi scan, ultrasound, or 4D-CT) to localize adenoma if surgery is being considered 3
• Check 24-hour urine calcium to exclude familial hypocalciuric hypercalcemia (FHH)—urine calcium will be low (<100 mg/24h) in FHH
• Consider parathyroid carcinoma if calcium >14 mg/dL with palpable neck mass

PTH Suppressed (PTH <20 pg/mL)

This indicates PTH-independent hypercalcemia. Proceed systematically:

1. Review all medications and supplements

   • Thiazide diuretics, lithium, calcium supplements, vitamin D, vitamin A
   • Discontinue any potentially causative agents 4

2. Assess for malignancy (accounts for ~45% of PTH-independent cases)

   • Obtain PTHrP level if malignancy suspected
   • Check serum protein electrophoresis for multiple myeloma
   • CT chest/abdomen/pelvis if no known malignancy
   • Most common: breast, lung, renal cell carcinoma, multiple myeloma 5, 1

3. Measure vitamin D metabolites

   • 25-hydroxyvitamin D
   • 1,25-dihydroxyvitamin D (calcitriol)
   • Elevated calcitriol suggests granulomatous disease (sarcoidosis, tuberculosis) or lymphoma 5

4. Check thyroid function (TSH, free T4)

   • Hyperthyroidism can cause hypercalcemia

5. Consider adrenal insufficiency

   • Morning cortisol or ACTH stimulation test
   • Particularly if hypotension, hyperphosphatemia present 2

Severity Stratification

Classify severity to guide urgency of workup and treatment:

• Mild: Total calcium <12 mg/dL (<3 mmol/L)
• Moderate: Total calcium 12-14 mg/dL (3-3.5 mmol/L)
• Severe: Total calcium >14 mg/dL (>3.5 mmol/L) 5, 1

Severe hypercalcemia requires immediate intervention before completing the full diagnostic workup 2.

Additional Diagnostic Considerations

Check serum phosphate pattern:

• Low phosphate → suggests primary hyperparathyroidism
• High phosphate → suggests vitamin D intoxication, adrenal insufficiency, or immobilization 2, 6

Assess for immobilization in bedridden patients or those with recent fractures.

Consider rare causes only after excluding common etiologies:

• Granulomatous diseases
• Milk-alkali syndrome
• Medications (immune checkpoint inhibitors, SGLT2 inhibitors, denosumab discontinuation)
• Extreme exercise or ketogenic diet 1

Common Pitfalls

• Do not assume malignancy without checking PTH first—primary hyperparathyroidism accounts for ~45% of all hypercalcemia cases and is easily missed 1

• Correct calcium for albumin if total calcium is measured: Corrected Ca = measured Ca + 0.8 × (4.0 - albumin). Better yet, measure ionized calcium directly 4

• Do not order a "shotgun" panel of tests—let PTH guide your workup to avoid unnecessary testing and delays 6

• Remember that PTH assays vary between laboratories—interpret results in context of your laboratory's reference range 7

• In hospitalized patients, consider drug-induced causes first before extensive malignancy workup, particularly thiazides and calcium/vitamin D supplementation 4