Result Interpretation

Accurate interpretation is crucial for proper diagnosis and management

Key Electrolytes
- Sodium, Potassium, Chloride, Bicarbonate (Total \(CO_2\)), Calcium, Magnesium, Phosphorus
Calculations
- Osmolality and Anion Gap

Key Electrolytes

General Considerations
- Reference Intervals: Always use the reference intervals established by the laboratory performing the tests
- Clinical Context: Interpret electrolyte results in the context of the patient’s clinical history, physical examination, and other laboratory findings
- Trends: Serial measurements are more valuable than single measurements for assessing electrolyte balance
Corrected Values: For some electrolytes (e.g., calcium), it may be necessary to correct the measured value based on albumin levels

Sodium (\(Na^+\))

Reference Interval: 136-145 mmol/L
Interpretation
- Hyponatremia (Serum \(Na^+\) < 136 mmol/L): Indicates excess water relative to sodium
  - Hypovolemic Hyponatremia: Sodium and water loss, with greater sodium loss
  - Euvolemic Hyponatremia: Normal sodium levels, but increased water retention
  - Hypervolemic Hyponatremia: Increased sodium and water retention, with water excess being greater
- Hypernatremia (Serum \(Na^+\) > 145 mmol/L): Indicates water deficit relative to sodium
  - Hypovolemic Hypernatremia: Water loss with greater sodium loss
  - Euvolemic Hypernatremia: Water loss with normal sodium levels
  - Hypervolemic Hypernatremia: Sodium gain with greater water gain
Clinical Significance
- Assessment of fluid balance and hydration status
- Evaluation of hormonal disorders (e.g., SIADH, diabetes insipidus)
- Diagnosis and management of kidney and heart failure

Potassium (\(K^+\))

Reference Interval: 3.5-5.1 mmol/L
Interpretation
- Hypokalemia (Serum \(K^+\) < 3.5 mmol/L): Indicates potassium depletion or cellular shift
  - Decreased Intake: Poor dietary intake
  - Increased Loss: Vomiting, diarrhea, diuretics
  - Cellular Shift: Insulin, alkalosis
- Hyperkalemia (Serum \(K^+\) > 5.1 mmol/L): Indicates impaired potassium excretion or cellular release
  - Decreased Excretion: Kidney failure, hypoaldosteronism
  - Cellular Release: Tissue damage, acidosis
  - Increased Intake: Potassium supplements
Clinical Significance
- Assessment of kidney function
- Evaluation of acid-base balance
- Diagnosis and management of cardiac arrhythmias

Chloride (\(Cl^-\))

Reference Interval: 98-107 mmol/L
Interpretation
- Hypochloremia (Serum \(Cl^-\) < 98 mmol/L): Indicates chloride depletion or increased bicarbonate levels
  - Loss of Chloride: Vomiting, nasogastric suctioning
  - Increased Bicarbonate: Metabolic alkalosis
- Hyperchloremia (Serum \(Cl^-\) > 107 mmol/L): Indicates chloride excess or decreased bicarbonate levels
  - Chloride Excess: Excessive saline infusion
  - Decreased Bicarbonate: Diarrhea, renal tubular acidosis
Clinical Significance
- Assessment of acid-base balance
- Evaluation of hydration status and kidney function

Total Carbon Dioxide (\(CO_2\))

Reference Interval: 22-33 mEq/L
Interpretation
- Decreased Total \(CO_2\): Suggests metabolic acidosis
- Increased Total \(CO_2\): Suggests metabolic alkalosis
Clinical Significance
- Screening test for acid-base disturbances
- Often used as a surrogate marker for bicarbonate

Calcium (\(Ca^{2+}\))

Reference Interval: 8.6-10.2 mg/dL (Total Calcium) or 4.6-5.6 mg/dL (Ionized Calcium)
Interpretation
- Hypocalcemia (Serum \(Ca^{2+}\) < 8.6 mg/dL): Indicates decreased calcium levels due to decreased PTH or vitamin D
  - Hypoparathyroidism: Decreased PTH production
  - Vitamin D Deficiency: Impaired calcium absorption
  - Kidney Disease: Decreased calcium reabsorption
- Hypercalcemia (Serum \(Ca^{2+}\) > 10.2 mg/dL): Indicates increased calcium levels due to increased PTH, vitamin D, or malignancy
  - Hyperparathyroidism: Increased PTH production
  - Malignancy: Bone metastasis, ectopic PTH production
  - Vitamin D Excess: Increased calcium absorption
Clinical Significance
- Assessment of bone metabolism
- Evaluation of parathyroid and kidney function
- Monitoring of malignancy

Magnesium (\(Mg^{2+}\))

Reference Interval: 1.7-2.2 mg/dL
Interpretation
- Hypomagnesemia (Serum \(Mg^{2+}\) < 1.7 mg/dL): Indicates magnesium depletion
  - Poor Dietary Intake: Malnutrition, alcoholism
  - Impaired Absorption: Malabsorption syndromes
  - Increased Excretion: Diuretics, hyperaldosteronism
- Hypermagnesemia (Serum \(Mg^{2+}\) > 2.2 mg/dL): Indicates impaired magnesium excretion
  - Kidney Failure: Decreased magnesium excretion
  - Excessive Magnesium Intake: Antacids, laxatives
Clinical Significance
- Assessment of kidney function
- Evaluation of cardiac arrhythmias and neuromuscular disorders

Phosphorus (\(P\))

Reference Interval: 2.5-4.5 mg/dL
Interpretation
- Hypophosphatemia (Serum \(P\) < 2.5 mg/dL): Indicates phosphate depletion
  - Decreased Intake: Malnutrition, alcoholism
  - Cellular Shift: Insulin, alkalosis
  - Increased Excretion: Hyperparathyroidism, diuretics
- Hyperphosphatemia (Serum \(P\) > 4.5 mg/dL): Indicates impaired phosphate excretion
  - Kidney Failure: Decreased phosphate excretion
  - Hypoparathyroidism: Decreased PTH production
  - Cellular Release: Tissue damage, hemolysis
Clinical Significance
- Assessment of kidney function
- Evaluation of parathyroid and bone metabolism
- Monitoring of tumor lysis syndrome

Calculations

Osmolality and Anion Gap are calculated parameters that provide additional information about electrolyte balance and acid-base status

Osmolality

Calculations:
- Conventional: \(Osmolality (mOsm/kg) = 2[Na^+] + \left( \frac {[Glucose (mg/dL)]} {18} \right) + \left( \frac {[BUN (mg/dL)]} {2.8} \right)\)
- SI: \(Osmolality (mmol/kg) = 2[Na^+] + [Glucose] + [Urea]\)
Reference Interval: 275-295 mOsm/kg
Interpretation
- Increased Osmolality: Dehydration, hypernatremia, hyperglycemia, uremia
- Decreased Osmolality: Overhydration, hyponatremia, SIADH
Clinical Significance
- Assessment of hydration status
- Evaluation of kidney function
- Detection of toxic substances (osmolal gap)

Anion Gap

Calculation: Anion Gap = [\(Na^+\)] + [\(K^+\)] - [\(Cl^-\)] - [\(HCO_3^-\)]
Reference Interval: 8-16 mEq/L (with \(K^+\)), 10-20 mEq/L (without \(K^+\))
Interpretation
- Elevated Anion Gap (Anion Gap Metabolic Acidosis)
  - Increased Production of Organic Acids: Ketoacidosis, lactic acidosis
  - Renal Failure: Accumulation of sulfates and phosphates
  - Toxic Ingestions: Methanol, ethylene glycol, salicylates
- Normal Anion Gap (Hyperchloremic Metabolic Acidosis)
  - Loss of Bicarbonate: Diarrhea, renal tubular acidosis (RTA)
  - Administration of Chloride-Containing Solutions: Saline infusion
Clinical Significance
- Differential diagnosis of metabolic acidosis
- Identification of specific causes of metabolic acidosis

Key Terms

Hyponatremia: A condition in which the blood contains too little sodium
Hypernatremia: A condition in which the blood contains too much sodium
Hypokalemia: A condition in which the blood contains too little potassium
Hyperkalemia: A condition in which the blood contains too much potassium
Hypochloremia: A condition in which the blood contains too little chloride
Hyperchloremia: A condition in which the blood contains too much chloride
Hypocalcemia: A condition in which the blood contains too little calcium
Hypercalcemia: A condition in which the blood contains too much calcium
Hypomagnesemia: A condition in which the blood contains too little magnesium
Hypermagnesemia: A condition in which the blood contains too much magnesium
Hypophosphatemia: A condition in which the blood contains too little phosphorus
Hyperphosphatemia: A condition in which the blood contains too much phosphorus
Glomeruli: Filtering units within the kidney
In Vitro: Taking place in a test tube, culture dish, or elsewhere outside a living organism
In Vivo: Occurring within a living organism
Hyponatremia: A condition in which the blood contains too little sodium
Hypovolemia: The medical term for a decrease in blood volume which results in decreased oxygen delivery to the body
Sepsis: A life-threatening condition that happens when your body’s response to an infection damages its own tissues and organs
Pulmonary Embolism: A blood clot that occurs in the lungs
Hepatitis: Inflammation of the liver
Metabolic Disorder: Occurs when abnormal chemical reactions in the body disrupt metabolism
Alveolar: Relating to the alveoli of the lungs
Bohr Effect: The effect of pH and CO2 on the oxygen-binding affinity of hemoglobin
Bilirubin: A yellow compound which occurs in the normal catabolic pathway that breaks down heme in vertebrates
Cations: A positively charged ion (e.g., \(Ca^{2+}\), \(Mg^{2+}\), \(K^+\), \(Na^+\))
Anions: A negatively charged ion (e.g., \(Cl^-\), \(HCO_3^-\), \(PO_4^{3-}\))
Electrolyte: An ion that conducts electrical impulses in solution

Calculations

Disease Correlation