Clinical Lab Values Overview

Clinical Pearls

• Normal lab values differ between labs and patients.
• Variations can occur due to techniques, reagents, age, gender, weight, and height.
• Lab errors, though uncommon, can happen.
• Potential causes include technical errors, improper calculations, inadequate specimens, incorrect sampling times, and medication interference.
• If an error is suspected, repeat the test.

Introduction

• Basic Metabolic Panel (BMP) or Chem-7, and Comprehensive Metabolic Panel (CMP) are initial lab tests.
• BMP includes sodium, potassium, chloride, carbon dioxide, glucose, blood urea nitrogen (BUN), and serum creatinine.
• CMP includes BMP plus albumin, alkaline phosphatase, alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, calcium, and magnesium/phosphorus.

Sodium (Na+)

• Normal range: 135 - 147 mEq/L.
• Most prevalent cation in extracellular fluid.
• Important for serum osmolarity, fluid balance, and acid-base balance.
• Crucial for nerve impulse transmission by maintaining electrical potential.

Clinical Significance - Sodium

• Hypernatremia: Increased sodium intake or fluid loss (e.g., gastroenteritis, diabetes insipidus, hyperaldosteronism).
• Hyponatremia: Decreased total body sodium or excess body water (e.g., heart failure, chronic renal failure, syndrome of inappropriate antidiuretic hormone secretion (SIADH), severe burns).

Potassium (K+)

• Normal range: 3.5 – 5 mmol/L.
• Main intracellular cation.
• Important for nerve excitability, acid-base balance, and muscle function.
• Serum potassium levels aren't always a perfect indicator of overall potassium balance.
• Significant effects on cardiac and neuromuscular function.

Clinical Significance - Potassium

• Hyperkalemia: Metabolic or respiratory acidosis, renal failure, dehydration, medications (ACE inhibitors, potassium supplements).
• Hypokalemia: Severe diarrhea/vomiting, respiratory alkalosis, alcohol abuse, Cushing's disease, medications (thiazide/loop diuretics, amphotericin B, insulin, albuterol).

Potassium - Magnesium

• Potassium and magnesium interact in the body's systems.
• Magnesium is involved in maintaining potassium balance.

Chloride (Cl-)

• Normal range: 95 – 105 mEq/L.
• Main extracellular anion.
• Passive role in fluid balance and acid-base balance.

Clinical Significance - Chloride

• Hyperchloremia: Metabolic acidosis, respiratory alkalosis, dehydration, diabetes insipidus, renal disorders.
• Hypochloremia: Prolonged vomiting, metabolic alkalosis, heart failure, SIADH, use of acid suppressants (H2 blockers, proton-pump inhibitors).

Carbon Dioxide (CO2)

• Normal range: 22 – 28 mEq/L.
• Represents the sum of dissolved carbon dioxide and bicarbonate ions (HCO3-) in serum (also known as bicarbonate or bicarb level).
• Regulates physiological pH.