Hypercalcemia: Etiology, Classification, Diagnosis, and Management

Vocabulary practice flashcards covering the etiology, pathophysiology, diagnostic classification, and therapeutic management of hypercalcemia.

Hypercalcemia

A condition characterized by elevated serum calcium levels, defined as a total serum calcium concentration of $> 10.5\,\text{mg/dL}$ or an ionized (free) calcium concentration of $> 5.25\,\text{mg/dL}$.

True Hypercalcemia

An elevation in physiologically active ionized calcium or calculated corrected calcium, regardless of total calcium concentration, which may produce clinical symptoms.

Factitious Hypercalcemia

An elevated total serum calcium level coexisting with normal ionized or corrected calcium levels, typically caused by elevated circulating binding proteins such as hyperalbuminemia in dehydrated patients or paraproteinemia in multiple myeloma.

Primary Hyperparathyroidism

A PTH-mediated cause of hypercalcemia resulting from autonomous PTH secretion by a parathyroid adenoma or parathyroid hyperplasia, driving renal synthesis of 1,25-dihydroxyvitamin D; it is typically asymptomatic.

Tertiary Hyperparathyroidism

A PTH-mediated form of hypercalcemia developing in the setting of chronic renal failure and end-stage renal disease (ESRD), where prolonged secondary hyperparathyroidism leads to autonomous, unregulated hyperfunction of one or more parathyroid glands.

Familial Hypocalciuric Hypercalcemia (FHH)

An autosomal dominant disorder caused by an inactivating mutation in the CaSR gene that impairs calcium-sensing receptor sensitivity in the parathyroid glands and kidneys, producing mild hypercalcemia, normal or elevated PTH levels, and hypocalciuria.

Hypercalcemia of Malignancy

A severe, non-PTH-mediated hypercalcemia typically presenting acutely due to paraneoplastic secretion of PTHrP (e.g., squamous cell carcinoma of the lung), osteolytic metastases, or extrarenal 1,25-dihydroxyvitamin D production.

Parathyroid Hormone-Related Protein (PTHrP)

A peptide secreted by various malignant tumor cells that mimics parathyroid hormone activity at bone and kidney receptors, representing the most common mechanism underlying hypercalcemia of malignancy.

Granulomatous Hypercalcemia

A non-PTH-mediated hypercalcemia seen in disorders such as sarcoidosis, driven by unregulated 1-alpha-hydroxylase activity in activated mononuclear cells that synthesizes 1,25-dihydroxyvitamin D independent of renal control.

Milk-Alkali Syndrome

A condition characterized by the triad of hypercalcemia, metabolic alkalosis, and renal insufficiency, precipitated by the ingestion of excessive quantities of calcium supplements and absorbable alkali (such as antacids).

Immobilization Hypercalcemia

A non-PTH-mediated elevation of serum calcium resulting from the lack of weight-bearing mechanical stress, triggering osteoclastic bone resorption and bone demineralization, primarily occurring in individuals with high baseline bone turnover.

Mild Hypercalcemia

A calcium disturbance defined as a total serum calcium of $10.5\text{--}12\,\text{mg/dL}$ or an ionized calcium of $5.25\text{--}8\,\text{mg/dL}$, which is typically asymptomatic.

Moderate Hypercalcemia

A calcium disturbance defined as a total serum calcium of $12\text{--}14\,\text{mg/dL}$ or an ionized calcium of $8\text{--}10\,\text{mg/dL}$, which may present asymptomatically or symptomatically depending on its rate of rise.

Severe Hypercalcemia (Hypercalcemic Crisis)

A medical emergency defined by a total serum calcium of $> 14\,\text{mg/dL}$ or an ionized calcium of $> 10\,\text{mg/dL}$, frequently presenting with profound dehydration, oliguria, anuria, altered mental status, psychosis, or coma.

Corrected Calcium Formula

$\text{Corrected calcium (mg/dL)} = \text{measured total } Ca^{2+}\,(\text{mg/dL}) + [0.8 \times (4 - \text{albumin concentration in g/dL})]$. It accounts for shifts in protein binding, though direct ionized calcium measurement is favored in major acid-base disorders.

Serum Intact PTH Level

The essential initial diagnostic test for confirmed hypercalcemia lacking an obvious cause, used to classify the condition as PTH-mediated (normal or elevated PTH) versus non-PTH-mediated (suppressed or low PTH).

Urine Ca/Cr Clearance Ratio

An index of renal calcium excretion used to differentiate primary hyperparathyroidism from familial hypocalciuric hypercalcemia; values $< 0.02$ indicate low fractional calcium clearance consistent with FHH.

Calcitonin

A rapidly acting, short-term antiresorptive agent used in the initial management of severe or symptomatic hypercalcemia to lower serum calcium levels quickly.

Bisphosphonates (Zoledronic Acid, Pamidronate)

Long-acting antiresorptive medications used for the sustained control of hypercalcemia by blocking osteoclastic activity; they have a slower onset of action and are contraindicated in patients with severe renal failure ($\text{CrCl} < 30\,\text{mL/min}$).

Denosumab

A bone-resorption inhibitor preferred over IV bisphosphonates as monotherapy for hypercalcemia of malignancy, and also used as an alternative agent when bisphosphonates are contraindicated due to severe renal impairment.

Cinacalcet

A calcimimetic agent that increases the sensitivity of calcium-sensing receptors, utilized in symptomatic familial hypocalciuric hypercalcemia or for primary/tertiary hyperparathyroidism in patients unable to undergo parathyroidectomy.

Thiazide Diuretics (Effect on Calcium)

Diuretics that enhance tubular calcium uptake and reduce renal calcium clearance, known to trigger or exacerbate hypercalcemia, and which must be discontinued during hypercalcemic states.

Loop Diuretics (Effect on Calcium)

Diuretics (such as furosemide) that induce renal calcium excretion ('lose calcium'), reserved in hypercalcemia management strictly for patients developing volume overload during aggressive IV saline repletion.