Hypocalcemia

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)