SODIUM

ELECTROLYTES

Electrolytes

• Substances whose molecules dissociate into ions when they are placed in water.

• Osmotically active particles

Classification of ions: by charge

General dietary requirements

• Most need to be consumed only in small amounts as utilized

• Excessive intake leads to increased excretion via kidneys

• Excessive loss may result in need for corrective therapy

  • Loss due to vomiting / diarrhea; therapy required - IV replacement, Pedilyte, etc.

ELECTROLYTE FUNCTIONS

ELECTROLYTE PANEL

Panel consists of:

1. Sodium (Na) 

2. Potassium (K)

3. Chloride (Cl)

4. Bicarbonate CO2 (in its ion form = HCO3-)

   • We did not measure bicarbonate directly, we measure the O2 first

• Oral hydration 

  • Salt

  • Sugar

  • 1 L water

ANALYTES OF THE ELECTROLYTE 

PANEL

1. Sodium (Na)

• The major cation of extracellular fluid

• Most abundant (90 %) extracellular cation

• Diet 

  • Easily absorbed from many foods

FUNCTION: SODIUM

• Influence on regulation of body water 

  • Osmotic activity 

    • Sodium determines osmotic activity 

    • Main contributor to plasma osmolality

• Neuromuscular excitability

  • Extremes in concentration can result in neuromuscular symptoms

• Na-K ATP-ase Pump 

  • AKA: sodium symporter

  • Pumps Na out and K into cells 

  • Without this active transport pump, the cells would fill with Na+ and subsequent osmotic pressure would rupture the cells

REGULATION OF SODIUM

• Plasma sodium Concentration depends on:

  • Plasma osmolality 

  • Intake of water in response to thirst

  • Excretion of water due to blood volume or osmolality changes 

• Renal regulation of sodium

  • Kidneys can conserve or excrete Na+ content depending on:

    • ECF and 

    • Blood volume

  • Kidneys  regulate sodium

    • by aldosterone

      • Controls NA+ reabsorption in Loop of Henle & Distal tubule

    • Land the renin-angiotensin system

      • This system will stimulate the adrenal cortex to secrete aldosterone

REFERENCE RANGES:

SODIUM 

• Serum

  • 136-145 mEq/L or mmol/L

• Urine (24 hour collection)

  • 40-220 mEq/L

SODIUM 

• Urine testing & calculation:

  • Because levels are often increased, a dilution of the urine specimen is usually required.

  • Once a number is obtained, it is multiplied by the dilution factor and reported as (mEq/L or mmol/L) in 24 hr.

DISORDERS OF SODIUM HOMEOSTASIS 

HYPONATREMIA

1. Due to increased Na+ loss

• Aldosterone deficiency

  • Hypoadrenalism

  • The action of aldosterone is to reabsorb the sodium and water, so if there is a decrease in aldosterone mababa din ung maaabsorb na sodium and water

• Diabetes mellitus 

  • In acidosis of diabetes, Na is excreted with ketones

• Potassium depletion 

  • K normally excreted , if none, then Na

• Loss of gastric contents

2. Due to increased water retention

• Dilution of plasma Na+

• Renal failure

  • If renal failure occurs, the kidneys ultimately fail to concentrate the urine, resulting to hyponatremia

• Nephrotic syndrome

  • Key features: excrete massive amounts of proteins → Hypoalbuminemia → Edema 

• Hepatic cirrhosis

  • Ascites: build up of fluids (ascitic fluid) → Enlarged tummy 

• Congestive heart failure

3. Due to water imbalance

• Excess water intake

• Chronic condition

Note:

• Increased lipids or proteins may cause false decrease in results. This would be classified as artifactual/pseudo-hyponatremia

  • Cause by hyperlipidemia and hyperproteinemia 

CLINICAL SYMPTOMS OF HYPONATREMIA

1. Depends on the serum level

• Can affect

  • GI tract

  • Neurological 

    • Nausea, vomiting, headache, seizures, coma

HYPERNATREMIA 

1. Due to excess water loss 

• Sweating

• Diarrhea

• Burns

• Diabetes insipidus

2. Due to increased Na intake/retention

• Excessive IV therapy 

3. Due to decreased water intake

• Elderly

• Infants

• Mental impairment

CLINICAL SYMPTOMS OF HYPERNATREMIA

• Involve the CNS

  • Altered mental status

  • Lethargy

  • Irritability

  • Vomiting

  • Nausea

SPECIMEN COLLECTION: SODIUM 

• Serum (slt hemolysis is OK, but not gross)

• Heparinized plasma

• Timed and random urine

• Sweat

• GI fluids

• Liquid feces (would be only time of excessive loss)

Sodium Determination 

Methods

1. Emission Flame Photometry 

2. Atomic Absorption Spectrophotometry

3. Ion Selective Electrode (Glass Aluminum silicate) - most commonly used method 

4. Colorimetry (Albanese Lein)

Flame Emission Spectrophotometry (FES) 

• AKA: Flame Photometer 

• Intense yellow

• Measurement of light emitted when the element is excited by energy in the form of heat.

• Na emits λ 589 nm (yellow)

• Use internal standard of lithium or cesium

• Possible for a dilutional error to occur in some flame photometer systems, but literature does not dwell on it

Atomic Absorption Spectrophotometry (AAS)

• Determines sodium concentration by measuring how much light sodium atoms absorb at a specific wavelength

ION SELECTIVE ELECTRODE

• Selective membrane at the ion selective electrode, allows measured ions to pass, but excludes the passage of the other ions

• Most routinely used method in clinical laboratories

• Membrane composition = lithium aluminum silicate glass

• Use chemical sensors detecting selective ions

• Uses a semipermeable membrane to develop a potential produced by having different ion concentrations on either side of the membrane

  • Semi-permeable membrane allows sodium ions to cross 300X faster than potassium and is insensitive to hydrogen ions.

  • Activity of the ion is being measured

• Two types:

  • Direct electrodes 

    • Use undiluted specimen on the surface

    • Gives the truest results 

  • Indirect electrodes 

    • Requirements to dilute first the sample using suitable buffered

    • Give lower results (called dilutional effect)

• Affected by:

  • Lipids 

    • If patients have hyperlipidemia, it will affect the results of Indirect ISE

  • Proteins