Definition: serum [Ca2+] <8.5 mg/dL, ionized <1.15 mmol/L.

Correct for hypoalbuminemia:

• For every 1 g/dL decrease in albumin, increase the Ca2+ level by 0.8 mg/dL. 
  • (4 - measured albumin)*0.8 + measured Ca2+ = corrected Ca2+.
• This correction is unreliable farther from normal range. If albumin is <2, check ionized Ca2+.
• Also consider checking ionized Ca2+ directly if clinical status is rapidly changing or if therapeutic decisions depend on calcium status.

Etiology/Risk Factors

• Common in hospitalized patients, particularly ICU patients.
• HIPOCALC mnemonic:
  • H: hypoparathyroidism, hypo/hypermagnesemia, hyperphosphatemia, hungry bone syndrome (hyperparathyroidism patients who undergo parathyroidectomy).
  • I: infection, especially gram negative sepsis (e.g., meningococcemia).
  • P: pancreatitis.
  • O: overload (rapid intravascular volume expansion), osteoblastic mets (prostate, breast).
  • C: chronic kidney disease (most common cause) or other vitamin D deficient states. In CKD, there is decreased production of active vitamin D (1,25-OH vitamin D), which causes  decreased intestinal Ca2+ absorption.
  • A: absorption abnormalities.
  • L: loop diuretics (increase renal excretion of Ca2+).
  • C: citrate-containing products (e.g. pRBCs, anti-coagulant for CVVH/CVVHD, during collection process for stem cell mobilization). 
• As pH increases, more Ca2+ binds to albumin, decreasing the ionized Ca2+ level. For this reason, alkalosis can cause or exacerbate symptoms of hypocalcemia.

Evaluation

• Laboratory tests:
  • Consider checking an ionized calcium to confirm. 
  • Chem 10.
  • Albumin.
  • PTH.
  • 25-OH Vitamin D level.
• Evaluate for symptoms to determine urgency of treatment.
  • CNS: lethargy, confusion, seizures.
  • Cardiac: QT prolongation.
  • Peripheral nervous system: paresthesias, tetany (especially carpopedal spasm).
    • Trousseau’s sign (carpal spasm occurring after the occlusion of the brachial artery with a blood pressure cuff for 3 minutes).
    • Chvostek sign (contraction of the facial muscle in response to tapping the facial nerve anterior to the ear).

Management

• Treatment of hypocalcemia depends on the chronicity and underlying cause.
  • In the acute/inpatient setting, hypocalcemia is often not treated unless the patient is symptomatic or calcium is expected to decrease significantly in the near future (i.e. post-parathyroidectomy with hungry bone syndrome). Also consider calcium replacement if patient is critically ill or hypotensive.
  • For patients who do not need urgent replacement, can give orally. Also consider vitamin D supplementation. Patients with CKD stage ≥4 may need active vitamin D, but this should only be given in consultation with nephrology.
• Dosing:
  • IV: max 10 mEq/hr. Give 5-15 mEq at a time, more if necessary. Calcium chloride has 14 mEq/gram and generally requires a central line. Calcium gluconate has 4.65 mEq/gram. 
  • PO: CaCO3 500-1000 mg TID between meals (to maximize absorption).
• Other tips: 
  • Correct hypomagnesemia.
  • Use caution repleting calcium in the setting of hyperphosphatemia to avoid calcium phosphate precipitation.

Key Points

• Always correct calcium for albumin.
• Hypocalcemia is common in the hospital, but rarely merits treatment.  
• Look for symptoms (tetany, EKG changes) to guide need for IV replacement.

Bushinsky DA, Monk RD. Electrolyte quintet: Calcium. Lancet 1998;352:306-311.