Hypocalcemia

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Hypocalcemia

  • General
    • Serum total Calcium < 8.5 or ionized <1.1
      • Ionized: <0.8 warrants treatment, <0.65 is critically low
    • Corrected serum calcium is calculated by adding 0.8mg/dl x difference below the reference of 4.1 g/dl in albumin
      • Pseudohypocalcemia
        • Total Calcium is reduced due to decreased albumin but ionized calcium is normal
  • Causes
    • Hypoparathyroidism (MCC)
      • Autoimmune Disease
      • Malignant or infectious infiltrate (hemochromatosis or Wilson disease)
      • Thyroidectomy
      • DiGeorge Syndrome
      • CaSR gene defect
    • Thyroid Surgery (hypoparathyroidism), acute pancreatitis, sepsis, tumor lysis syndrome, Acute Alkalosis (increase in albumin binding calcium), Chelation (blood (citrate) transfusion, EDTA, Calcium binding Meds (Foscarnet, Citrate, Fluoroquinolones))
      • High Volume blood transfusion (citrate)
        • Hepatic or renal failure at greatest risk
    • CRRT, Leukapheresis, Plasmapheresis, Massive Transfusion
    • Ethylene Glycol poisoning
    • Magnesium abnormality (especially hypomagnesemia)
    • Impaired 1,25-VitD production with Hyperphosphatemia from CKD
      • MCC of acquired hypocalcemia
    • Rhabdomyolysis/Tumor Lysis increase binding of phos and calcium
      • Low ionized calcium
    • Prostate/Breast Cancer
    • Anticonvulsants (Phenytoin, Phenobarbital, Carbamazepine)
      • INH, rifampin, pentamidine, aminoglycosides
      • Loops
      • Bisphosphonates, calcitonin, cisplatin, 5-FU
      • Cinacalcet
  • Symptoms
    • Moderate:
      • Peri-oral tingling, paresthesia, Tetany
      • Hyperreflexia
      • Muscle weakness, cramping, myalgias, fasiculations
      • Chvostek Sign (facial spasm by tapping near the patient’s facial nerve)
      • Trousseau Sign (carpopedal spasm when a sphygomometer is tightened on the arm for more than 3 minutes)
    • Severe: Seizures, laryngospasm, confusion, bradycardia, decompensated HF
      • Prodrome may be absent prior to death
      • Hypotension, Heart block
      • QT prolongation
        • Slower influx means it takes longer for intracellular calcium to reach the threshold to close L-type Ca2+ channels, extending AP duration, extending QT
  • Diagnosis: Remeasure and measure albumin for corrected calcium level < ionized calcium
    • Magnesium and Phosphate
    • Calcidiol (25-Hydroxy VitD) and Calcitriol (1,25-Hydroxy VitD)
      • Low 25-Hydroxy VitD indicated VitD deficiency
      • Low 1,25-Hydroxy VitD indicate renal failure, hypoparathyroidism
    • Lipase
    • CK if K+ and phos are elevated
    • Measure PTH
      • Hypocalcemia + Low/Normal PTH: Hypoparathyroidism
      • Hypocalcemia + Elevated PTH: Renal Failure, VitD deficiency, PTH resistance, intravascular chelation
  • Treatment
    • 1) Symptoms
      • Tetany, carpopedal spams, laryngospasm, long QT, seizures, arrythmias
    • 2) QT prolongation without hypokalemia or hypomagnesemia
    • 3) Severe Hypocalcemia (iCa2+ < 0.8)
    • Don’t treat:
      • Mild-moderate pts who are critically ill
      • Hyperphosphatemia: increases precipitation of calcium phosphate (calciphylaxis)
      • Ethylene glycol poisoning: calcium oxalate in the brain
    • Ca2+ ≥7.5 g/dl:
      • 1) Oral Calcium Carbonate 1-3g q6hr-q12hr > Calcium Citrate > Calcium Gluconate
      • 2) Calcitriol (1,25-Dihydroxyvitamin D) 1000-4000IU per day
    • Ca2+ <7.5 g/dl or severe:
      • 1) IV Calcium Gluconate 2-3g peripheral > Calcium Chloride 1g Central
        • Over 10-20 minutes, may need to repeat (slow via central IV)
        • SE: Nausea, vomiting, hypertension, flushing, chest pain
        • Pancreatitis/still falling: 1g Calcium gluconate over 60 minutes, q1hr prn
    • Monitor for hypercalciuria (limits therapy)
      • Add thiazide
        • Teriparatide 20 nanograms BID rapidly eliminates hypocalcemia in acute post-surgical patients
        • Dialysis vs binders may be preferred if Severe Hyperphosphatemia
        • 100-200mg over 10-20mins (bolus) + slow infusion of 0.5-1 up to 2 mg/kg/hr as 10% calcium gluconate until Ca at 8-9
      • Chronic: VitD supplementation (50k weekly)

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