1st-order laboratory parameters-obligatory laboratory tests.
- Electrolytes – calcium in serum/albumin or alternatively ionized calcium.
Laboratory parameters 2nd order – depending on the results of the history, physical examination, etc. – for differential diagnostic clarification.
- Parathyroid hormone [↑], inorganic phosphate [in serum ↓; in urine ↑], alkaline phosphatase [↑ if bone involvement] – suspected hyperparathyroidism, primary (pHPT; parathyroid hyperfunction).
- Renal parameters – urea, creatinine, cystatin C if necessary.
- Parathyroid hormone-related peptide (PTHrP)/parathyroid hormone-related protein – suspected paraneoplastic syndrome.
- Thyroid parameter (TSH) – suspected hyperthyroidism (hyperthyroidism).
- Cortisol, ACTH, possibly ACTH kurtest (Synacten test) – suspected Addison’s disease (primary adrenocortical insufficiency / adrenocortical weakness).
- Vitamin D serum level (25-hydroxy vitamin D) – suspected vitamin D intoxication.
- Calcium excretion in 24-h urine – suspected familial benign hypocalciuric hypercalcemia (FBHH) [low excretion of calcium in urine].
Further indications
The most important laboratory test for differential diagnosis (DD) of hypercalcemia is the determination of intact parathyroid hormone (iPTH):
- IPHT ↑ or inadequate in the upper normal range → suspicion of primary hyperparathyroidism (pHPT; parathyroid hyperfunction)DD familial benign hypocalciuric hypercalcemia (FBHH) (rare), for DD determination of calcium excretion in 24h urine and calculation of calcium clearance/creatinine clearance: quotient < 0.01 FHH; quotient > 0.01 pHPT.
- IPTH ↓ → no pHPT → suspected tumor hypercalcemia until proven otherwiseNote: Even low-grade (multiple proven) hypercalcemia requires further clarification!
- 1,25-dihydroxy vitamin D – determination if no tumor is present.
- Normal: e.g. Paget’s disease, immobilization.
- Increased: e.g. sarcoidosis, tuberculosis
