Life-Threatening Electrolyte Abnormalities

Diagnosis

Indications for Testing

Suspected electrolyte abnormality (eg, patient with loss of consciousness, or patient receiving diuretic therapy)

Laboratory Testing

• Evaluate whether elevation or decrease is real
  • Hyperkalemia – evaluate for hemolysis in sample
  • Hyponatremia – evaluate for presence of hyperglycemia or hyperlipidemia
• Initial screen – panel should include Na, potassium chloride, bicarbonate, blood urea nitrogen (BUN), creatinine, glucose, and Ca
• Mg
  • Order concurrently in high-risk situations (eg, diabetes mellitus, alcoholism, diuretic therapy)
• Albumin
  • Order serum test concurrently if calcium abnormality suspected
  • If hypocalcemia suspected – also order Mg
• For further evaluation, refer to hypocalcemia

Differential Diagnosis

Refer to individual topics in Background.

Background

Electrolytes

• Ca
  • Normal ranges
    • Serum Ca – 8.4-10.2 mg/dL
    • Ionized Ca – 1.11-1.30 mmol/L
      • Needs correction for pH outside of normal range
  • Serum Ca measurement is directly related to serum albumin unless measured as ionized (total Ca directly proportional to albumin concentration)
    • Recommend following ionized Ca level in patients in intensive care unit (ICU) or in any clinical setting in which albumin concentration is significantly altered
    • Corrected serum Ca (for albumin) – CCa = (4 g/dL-plasma albumin) x 0.8 + serum Ca
  • Ca-related disorders
    • Hypocalcemia – defined as <8.4 mg/dL (serum) or <1.11 mmol/L (ionized)
      • Symptoms
        • Tetany – latent tetany may result in Trousseau and Chvostek signs
          • Trousseau sign – inflating blood pressure cuff on arm for 3 minutes to systolic blood pressure will cause spasm of hand
          • Chvostek sign – tapping on facial nerve near temporal mandibular joint will cause grimace and spasm of facial muscles
        • Seizures
        • Circumoral numbness
        • Paresthesias
        • Carpopedal spasm
        • Electrocardiogram (ECG) – prolonged QT interval, Torsades de Pointes
      • Etiologies
        • Removal or destruction of parathyroid glands (hypoparathyroidism)
        • Hyperphosphatemia secondary to rhabdomyolysis or renal failure
        • Pancreatitis
        • Hypovitaminosis D (liver, kidney disease)
        • Parathyroid hormone (PTH) resistance secondary to hypomagnesemia (Mg <1.0 mg/dL)
    • Hypercalcemia – defined as ≥10.3 mg/dL (serum) or >1.30 mmol/L (ionized)
      • Symptoms
        • 10.3-12 mg/dL – stones, bones, psychic moans, and abdominal groans
        • >12 mg/dL – stupor and coma
        • >13 mg/dL – ECG shows QT interval shortening, prolongation of PR
        • >15 mg/dL – heart block, cardiac arrest
      • Etiologies
        • Cancer with bone metastasis (in particular prostate and breast)
        • Hyperparathyroidism, thyrotoxicosis
        • Drug induced
        • Granulomatous disease – sarcoidosis
• K
  • Normal range – 3.3-5.0 mmol/L
    • Rapid changes have life-threatening consequences – may affect serum pH (inverse relationship)
  • Three controlling mechanisms
    • Intake
    • Distribution
      • Intracellular and extracellular fluid
      • Cellular distribution affected by insulin beta-adrenergic receptors and renal excretion
    • Excretion
  • K-related disorders
    • Hypokalemia
      • Definition
        • Mild – 3-3.2 mmol/L
        • Moderate – 2.5-2.9 mmol/L
        • Severe – <2.5 mmol/L
      • Symptoms – may vary from asymptomatic to fulminant respiratory failure
        • Most common – weakness, fatigue
        • Electrocardiogram (ECG) – prolonged PR interval, Torsade de Pointes
      • Etiologies
        • Drugs (eg, diuretics, beta agonists)
        • Gastrointestinal losses
        • Renal losses (eg, osmotic diuresis, mineralocorticoid excess)
        • Hypomagnesemia
        • Dialysis/plasmapheresis
        • Inadequate intake (eg, anorexia, dementia)
        • Transcellular shifts (eg, alkalosis, hypothermia)
    • Hyperkalemia
      • Definition
        • Mild – >5.1-6.0 mmol/L
        • Moderate – 6.1-7 mmol/L
        • Severe – >7 mmol/L
      • Symptoms – usually occurs only >7 mmol/L
        • Muscle weakness, cardiac arrhythmias
        • ECG – peaked T waves, widening of QRS, ventricular tachycardia
      • Etiologies
        • Sample collection error – usually hemolysis of specimen
        • Drugs (eg, angiotensin-converting ​​enzyme [ACE] inhibitors, potassium-sparing diuretics)
        • Rhabdomyolysis
        • Metabolic acidosis
        • Renal failure, renal tubular acidosis type IV
        • Hypoaldosteronism
        • Hypoglycemia
        • Tumor lysis syndrome
        • Addison disease
• Na
  • Normal range – 136-144 mmol/L
    • Consistent serum osmolality maintained through a balance of Na and water intake and excretion
    • Serum osmolality reference interval – 280-303 mOsm/kg
      • Calculated serum osmolality = (2 x Na) + (glucose/18) + (BUN/2.8)
  • Na-related disorders
    • Hyponatremia – defined as <135 mmol/L
      • Most often a chronic condition but may worsen in acutely ill patients
      • Symptoms – most often found in patients with abrupt changes in sodium level
        • Nausea/emesis
        • Headache
        • Lethargy
        • Severe hyponatremia – seizures, coma, death
      • Etiologies
        • Pseudohyponatremia
          • Hyperglycemia – for every 100 mg/dL increase of glucose, serum Na is lowered by 1.7 mmol/L
          • Hyperlipidemia
          • Hyperproteinemia (eg, multiple myeloma)
        • Hypovolemic – thiazide diuretics, osmotic diuresis, adrenal insufficiency, ketonuria, gastrointestinal (GI) losses
        • Euvolemic – syndrome of inappropriate antidiuretic hormone (SIADH), hypothyroidism, HIV, certain cancers, glucocorticoid deficiency
        • Hypervolemic – psychogenic polydipsia, congestive heart failure, cirrhosis, and renal failure
    • Hypernatremia – defined as >145 mmol/L
      • Symptoms – mimics symptoms of hyponatremia
      • Etiologies
        • Hypovolemic – body fluid losses, diuretic use, GI losses, heat injury, osmotic diuresis
        • Euvolemic – central diabetes insipidus, fever, mediating tumors
        • Hypervolemic – Cushing syndrome, hemodialysis, hyperaldosteronism, iatrogenic (eg, saline enemas)
• Mg
  • Normal range – 1.6-2.6 mg/dL
    • Aids in cellular transport of Ca, Na, K
    • Balance maintained by kidneys 
  • Mg-related disorders
    • Hypomagnesemia (common) – defined as <1.6 mg/dL
      • Symptoms – not usually evident until Mg <1.0 mg/dL
        • Neurologic manifestations similar to hypocalcemia
        • Tetany, muscle weakness, Chvostek, and Trousseau signs
        • Electrocardiogram (ECG) – widening QRS or QT and peaked T waves, premature ventricular contractions
      • Etiologies
        • Gastrointestinal losses – diarrhea, small bowel surgery, malabsorption, pancreatitis
        • Renal losses – diuretics, nephrotic drugs, tubular necrosis
        • Diabetes (uncontrolled)
    • Hypermagnesemia – defined as >2.6 mg/dL
      • Rare disorder – usually mild elevation with no symptoms
      • Kidneys able to rapidly respond if functioning normally
      • Symptoms – occur when Mg ≥4 mg/dL
        • 4-6 mg/dL – nausea, lethargy, flushing
        • 6-10 mg/dL – somnolence, hypocalcemia, hypotension, bradycardia
        • >10 mg/dL – respiratory paralysis, complete heart block, cardiac arrest
      • Etiologies
        • Impaired renal function
        • Large load of Mg or Mg-containing drugs
        • Parenteral Mg therapy for preeclampsia
        • Elderly patient with gastrointestinal disease receiving cathartics