Electrolytes

Electrolytes Electrolytes are anions or cations

Functions of the electrolytes

• Maintenance of osmotic pressure and water distribution

• Maintenance of the proper pH

• Regulation of the proper function of the heart and other muscles

• Involvement in oxidation –reduction reactions

• Cofactors for enzymes

Sodium Sodium ions are the major cations of extracellular fluid

Clinical significance: • Hyponatremia (decreased plasma Na concentration)

- Unusual losses due to excessive sweating, prolonged vomiting, or persistent diarrhea

- Renal loss due to diuretics, deficiency of aldosterone, or severe polyuria

- Excessive retention of water (dilutional type) due to chronic cardiac failure, hepatic cirrhosis, nephrotic

syndrome and malnutrition .

NB : Pseudohyponatremia is analytical artifact that may be seen with lipemic specimens

• Hypernatremia (increased plasma Na concentration)

due to:

Eg: - Parenteral therapy with saline solutions

- Hyperaldosteronism

Specimens: Serum, heparinized plasma, whole blood, sweat, urine,

feces, or gastrointestinal fluids may be assayed . Stored at 2 to 4 C or frozen for delayed analysis

Determination of sodium in body fluids :• Electrochemically with an ion-selective

electrode (ISE)

• Flame emission spectrophotometry (FES)

• Spectrophotometric methods

Reference Intervals : 136 to 145 mmol/L

Potassium

Potassium is the major intracellular cation

Clinical significance:• Hypokalemia (decreased plasma K concentration)

- decrease intake eg : starvation

- redistribution of extracellular K into intracellular fluid

eg: with insulin therapy , alkalosis

- increase loss of K: ♦ GI loss (vomiting, or diarrhea)

♦ renal loss (diuretics eg:thiazides)

• Hyperkalemia (increase plasma K concentration) - IV infusion of K - Transfer of intracellular K into extracellular fluid occur

in cases of dehydration, acidosis, or severe burns .

- Decreased excretion of K in acute renal failure or end stage renal failure

Specimens : for serum or plasma assay of K must be collected in such a way as to minimize hemolysis

(release of K from erythrocytes can increase the serum level )

Determination of potassium in body fluids :• Atomic absorption spectroscopy • Electrochemically with an ion-selective electrode (ISE) • Flame emission spectrophotometry (FES)• Spectrophotometric methods

Reference Intervals :

- For serum of adults 3.5 to 5.1 mmol/L- For serum of newborns 3.7 to 5.9 mmol/L

•

ChlorideChloride is the major extracellular anion

Hypochloremia (decreased plasma Cl concentration)

Is observed in salt-losing nephritis as associated with chronic pyelonephritis

Hyperchloremia (increased plasma Cl concentration )

Occurs with dehydration, renal tubular acidosis, and acute renal failure

Determination of chloride in body fluids

Specimens: chloride is measured in serum or plasma, urine,

and sweat

• Spectrophotometric Methods

• Ion-Selective Electrode Methods

Bicarbonate (total carbon dioxide)Clinical Significance :• Alterations of HCO3- and CO2 dissolved in plasma are

characteristic of acid-base imbalance • When acid-base imbalance is suspected, evaluation of

blood gases and pH is required .

- Increase in CO2 occur in metabolic alkalosis due to: eg: severe vomiting hypokalemic states - Decrease in CO2 are seen in: eg: renal failure

Methods for The determination of serum or plasma total carbon dioxide

The first step in many automated methods is the acidification of the sample to convert the various forms of CO2 in plasma to gaseous CO2

• Enzymatic method • Direct ISE method