Hypercalcemia — Severity Classifier

Use this skill the moment a high serum calcium is reported, before launching workup or treatment.

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STEP 1 — Confirm the calcium is real

Before grading, rule out pseudo-hypercalcemia:

• Apply albumin correction: Corrected Ca (mg/dL) = measured total Ca + [(4.0 − serum albumin g/dL) × 0.8] (or in SI units: Corrected Ca mM = measured total Ca + [(40 − albumin g/L) × 0.02])
• If serum albumin is high (dehydration / haemoconcentration) → suspect pseudo-hypercalcemia.
• If pH is significantly altered (acidosis lowers, alkalosis raises Ca²⁺ binding) → measure ionized calcium directly.
• Reference range total Ca: 8.5–10.5 mg/dL (2.12–2.62 mM). Ionized Ca: 4.65–5.25 mg/dL (1.16–1.31 mM).

If still hypercalcemic on corrected or ionized values → proceed to Step 2.

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STEP 2 — Stratify by calcium level

Severity	Corrected Ca (mg/dL)	Corrected Ca (mM)
Mild	10.5 – 12.0	2.62 – 3.0
Moderate	12.0 – 14.0	3.0 – 3.5
Severe	> 14.0	> 3.5

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STEP 3 — Layer in acuity and symptoms

Tolerance depends on how fast the calcium rose, not just the number.

Acute hypercalcemia (rapid rise) — typically symptomatic at lower levels

• GI: anorexia, nausea, vomiting
• Renal: polyuria, polydipsia, dehydration, AKI
• Neuro: depression, confusion, hyporeflexia, stupor, coma
• Cardiac: short QT, prolonged PR, widened QRS, bradycardia, digitalis sensitivity, arrhythmia

Chronic hypercalcemia (gradual rise) — milder, often "asymptomatic"

• GI: dyspepsia, constipation, pancreatitis
• Renal: nephrolithiasis, nephrocalcinosis, slow CKD progression
• Neuro: weakness, lethargy
• Cardiac: hypertension

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STEP 4 — Final classification & action

Final grade	Trigger	Action
Asymptomatic mild (Ca <12, no symptoms)	Most outpatient PHPT	Treat the underlying cause. Avoid Ca >1000 mg/d intake, immobilisation, thiazides. Outpatient workup.
Symptomatic moderate (Ca 12–14 + symptoms) OR any moderate with rapid rise	Often MAH, severe PHPT	Admit. Start hydration ± antiresorptive. Workup in parallel.
Severe (Ca >14, or any level with stupor / coma / arrhythmia / AKI)	Hypercalcemic crisis	Medical emergency. ECG, IV access, normal saline bolus, denosumab or IV bisphosphonate, ± calcitonin for rapid drop, consider dialysis if refractory or renal failure.

Patients with serum Ca >14 mg/dL (3.5 mM) are almost always symptomatic and need urgent measures.

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CLINICAL GUARDRAILS

• Albumin-corrected calcium is approximate, not exact — when in doubt, get an ionized calcium.
• A "normal" total calcium with low albumin can still be true hypercalcemia. Check the corrected value.
• A patient with mildly elevated calcium but new confusion is severe, regardless of the number. Acuity > level.
• Don't anchor on "asymptomatic" — patients minimise polyuria, constipation, mood change. Ask specifically.
• ECG is mandatory in severe hypercalcemia, especially if on digoxin — short QT and digitalis toxicity are real.
• Dehydration masks the calcium level. Rehydration may transiently raise corrected Ca by unmasking; always rehydrate before trusting a follow-up value.

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SOURCE

Bilezikian JP, Endotext. Approach to Hypercalcemia. NCBI Bookshelf NBK279129. Section: Definition of Hypercalcemia; Clinical Assessment; Table 2.