Electrolyte abnormalities are common in both outpatient and inpatient settings. Uncorrected electrolyte abnormalities may have life-threatening consequences. Important electrolytes include calcium (Ca), potassium (K), sodium (Na), and magnesium (Mg).
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
- Tetany – latent tetany may result in Trousseau and Chvostek signs
- 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)
- Symptoms
- 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
- Symptoms
- Hypocalcemia – defined as <8.4 mg/dL (serum) or <1.11 mmol/L (ionized)
- Normal ranges
- 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)
- Definition
- 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
- Definition
- Hypokalemia
- Normal range – 3.3-5.0 mmol/L
- Na
- Normal range – 136-145 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
- Pseudohyponatremia
- 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)
- Hyponatremia – defined as <135 mmol/L
- Normal range – 136-145 mmol/L
- 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)
- Symptoms – not usually evident until Mg <1.0 mg/dL
- 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
- Hypomagnesemia (common) – defined as <1.6 mg/dL
- Normal range – 1.6-2.6 mg/dL
ARUP Laboratory Tests
Evaluate electrolyte abnormalities and underlying hepatic or renal dysfunction
Quantitative Ion-Selective Electrode/Quantitative Enzymatic/Quantitative Spectrophotometry
Evaluate Mg concentrations in blood
Quantitative Spectrophotometry
Evaluate for kidney dysfunction in patients with known risk factors (eg, hypertension, diabetes, obesity, family history of kidney disease)
Quantitative Chemiluminescent Immunoassay/Quantitative Enzyme-Linked Immunosorbent Assay
Quantitative Ion-Selective Electrode/Quantitative Enzymatic/Quantitative Spectrophotometry
Panel includes Ca, carbon dioxide, chloride, creatinine, glucose, K, Na, and urea nitrogen
Quantitative Ion-Selective Electrode/Enzymatic
Panel includes anion gap carbon dioxide, chloride, K, and Na
Quantitative Ion-Selective Electrode
Panel includes Na, K, chloride, and creatinine
Diagnose and manage diabetes mellitus and other carbohydrate metabolism disorders
Quantitative Enzymatic
Use to correct for hypoalbuminemia on serum Ca level
Quantitative Spectrophotometry
Determine Ca concentrations
Quantitative Spectrophotometry
Ion-Selective Electrode/pH Electrode
Use for classification of Na disorders and evaluation of unmeasured ions
Freezing Point
May be useful in assessment of tissue stores
For routine assessment of Mg deficiency, plasma or serum Mg is preferred
Quantitative Inductively Coupled Plasma-Mass Spectrometry
Quantitative Ion-Selective Electrode
Quantitative Ion-Selective Electrode
Quantitative Ion-Selective Electrode
Quantitative Ion-Selective Electrode
Quantitative Spectrophotometry
Enzymatic
Quantitative Spectrophotometry
Quantitative Ion-Selective Electrode
Quantitative Ion-Selective Electrode
Quantitative Spectrophotometry
Medical Experts
Genzen

Lehman

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Panel includes albumin, alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, bilirubin, Ca, carbon dioxide, creatinine, chloride, glucose, K, protein, Na, and urea nitrogen