Electrolytes and Cardiac Biomarkers Overview

Sodium (Na+)

Major extracellular cation; maintains osmolality and fluid balance.

Potassium (K+)

Major intracellular cation; crucial for muscle and cardiac function.

Chloride (Cl-)

Extracellular anion; balances Na+ and HCO3-.

Bicarbonate (HCO3-)

Buffer system; maintains acid-base balance.

Hyponatremia

Causes include SIADH, fluid overload, diuretics.

Hypernatremia

Causes include dehydration, diabetes insipidus.

Regulation of Sodium

Aldosterone increases Na+ reabsorption; ADH conserves water.

Hypokalemia

Causes include vomiting, diarrhea, diuretics.

Hyperkalemia

Causes include renal failure, hemolysis, acidosis.

Pseudohyperkalemia

From hemolysis or prolonged tourniquet.

Chloride Shift

Chloride shifts with HCO3- to maintain electroneutrality.

Hypochloremia

Often follows vomiting (loss of HCl).

Bicarbonate Measurement

Measured as total CO2; reflects buffering capacity.

Anion Gap

Anion Gap = Na - (Cl + HCO3); normal ~10-14 mmol/L.

Increased Anion Gap

MUDPILES (e.g., lactic acidosis, ketoacidosis).

Decreased Anion Gap

Hypoalbuminemia, lab error.

Troponins (I and T)

Most sensitive and specific markers for MI; rise: 3-6 hrs, peak: 12-24 hrs, persist: 7-10 days.

CK-MB (Creatine Kinase-MB)

Rises 4-6 hrs after MI, peaks at 24 hrs, returns to normal in 48-72 hrs.

Myoglobin

Very early marker (1-2 hrs), but nonspecific; useful for early rule-out, but replaced by troponin clinically.

BNP and NT-proBNP

Secreted by ventricles in response to stretch (e.g., heart failure); higher values = worse heart failure.

hs-CRP

Marker of inflammation and cardiovascular risk.

Homocysteine and lipoprotein(a)

Emerging cardiac risk markers.