Electrolytes in Clinical Chemistry: Food Sources and Functions

Osmolality

Physical property of a solution based on the concentration of solutes, expressed as millimoles per kilogram of solvent (w/w).

Electrolytes

Ions capable of carrying an electric charge, found in blood, urine, tissues, and other body fluids.

Functions of Electrolytes

Regulate volume and osmotic balance, myocardial rhythm, enzyme activation, and acid-base balance.

Normal plasma osmolality

275 - 295 mOsm/kg of plasma H2O.

Sodium Food Sources

Processed foods, cheese, breads, cereals, sauces, pickled foods, commercial rice or pasta mixes, and condiments.

Potassium Food Sources

Green leafy vegetables (spinach, kale), tomatoes, cucumbers, pumpkin, carrots, potatoes, banana, avocado, beans, peas, milk, and yoghurt.

Chloride Food Sources

Seafood, seaweeds, rye, tomatoes, lettuce, celery, and olives.

Calcium Food Sources

Milk, milk alternatives, soya, nuts, and green leafy vegetables (broccoli, cabbage, okra).

Magnesium Food Sources

Legumes, nuts, seeds, fish, and whole grains.

Functions of Na, Cl, K

Volume and osmotic regulation.

Functions of K, Ca, Mg

Myocardial rhythm and contractility.

Functions of Ca, Mg, Zn, K, Cl

Important cofactors in enzyme activation.

Functions of Mg

Regulation of ATPase ion pumps.

Functions of K, Ca, Mg

Neuromuscular excitability.

Functions of Mg, PO₄

Production and use of ATP from glucose.

Functions of HCO3, K, Cl, PO4

Maintenance of acid-base balance.

Anion Gap Formula

Anion Gap = Na+ - (Cl- + HCO3-).

Osmolality Formula

Osmolality = Total moles of solute (millimoles) / Weight of solvent (kg).

AVP Response to Osmolality

A 1-2% increase in osmolality causes a fourfold increase in the circulating concentration of Arginine Vasopressin (AVP).

Electroneutrality

Fluids always contain equal numbers of cations and anions.

Disassociation of Solutes

Depends on the chemical composition of the compound and the concentration of other charged particles in the medium.

Hyponatremia

A condition characterized by low sodium levels in the blood.

Pseudohyponatremia

A laboratory artifact that results in falsely low sodium levels due to high lipid or protein levels.

Hypernatremia

A condition characterized by high sodium levels in the blood.

Serum Osmolality

275-295 mOsm/kg

Urine Osmolality (24h)

300-900 mOsm/kg

Urine/Serum Ratio

1.0-3.0

Random Urine Osmolality

50-1,200 mOsm/kg

Osmolal Gap

5-10 mOsm/kg

Hyponatremia

Low concentration of sodium <135 mmol/L, clinically significant if <130 mmol/L

Abnormal Blood Sodium Levels

Changes in blood sodium levels affect body water content, causing dehydration or edema.

Natrium

Present in all body fluids, found in highest concentration in blood and extracellular fluid.

Major extracellular cation

Sodium is a major contributor to osmolality and helps maintain osmotic pressure.

Sodium Regulation Processes

Intake of water in response to thirst, excretion of water, blood volume status.

Increased Na+ Loss Causes

Hypoadrenalism, potassium deficiency, diuretic use, ketonuria, salt-losing nephropathy, prolonged vomiting or diarrhea, severe burns.

Increased Water Retention Causes

Renal failure, nephrotic syndrome, hepatic cirrhosis, congestive heart failure, excess water intake.

Water Imbalance

Can be due to vasopressin hormone secretion or syndrome of inappropriate arginine vasopressin (SIADH).

Classification of Hyponatremia

Can be classified according to serum/plasma osmolality: low, normal, or high osmolality.

Low Osmolality Hyponatremia Causes

Increased sodium loss, increased water retention, increased non-sodium cations, lithium excess, increased gamma globulins-cationic.

Normal Osmolality Hyponatremia Causes

Severe hyperkalemia, severe hypermagnesemia, severe hypercalcemia, pseudohyponatremia, hyperlipidemia, hyperproteinemia.

High Osmolality Hyponatremia Causes

Hyperglycemia, mannitol infusion.

Pseudohyponatremia

Reduction of serum sodium concentration due to systematic error in measurement, often caused by excess lipids in serum.

Symptoms of Hyponatremia

125-130 mmol/L: GI symptoms; <125 mmol/L: nausea, vomiting, muscular weakness, headache, lethargy, ataxia; severe cases can lead to seizures, coma, and death.

Acute Hyponatremia

Considered a medical emergency if serum sodium <120 mmol/L for 48h or less.

Hypernatremia

High sodium levels in the blood.

Sodium level

>145 mmol/L.

Mortality rate at sodium level >160 mmol/L

Associated with a mortality rate of 60-75%.

Causes of Hypernatremia

Due to excessive loss of water relative to Na+ loss, decreased water intake, or increased Na+ intake or retention.

Correction of sodium levels

Should be corrected very slowly since the brain is very sensitive to water movement.

Hypoosmolality

Low sodium levels in the blood and low sodium levels in the brain.

Common Treatment for Hypoosmolality

Give sodium (~10 mmol per 24 hours).

Osmolar Demyelination Syndrome (ODS)

Occurs when sodium is rapidly supplied to the blood vessels, causing water to travel from the brain to the blood vessels.

Hyperosmolality

High sodium levels in the blood and high sodium levels in the brain.

Common Treatment for Hyperosmolality

Give water.

Cerebral edema

Occurs when water is rapidly supplied to the blood vessels, causing water to travel from the blood vessels to the brain.

Fast correction of sodium levels

Can cause brain injury.

Chronic hypernatremia in alert patients

Indicative of a hypothalamic disease.

Adipsia

Inadequate water intake due to hypothalamic dysfunction.

Sodium determination specimen types

Serum, plasma, urine (24h), sweat.

Ion-Selective Electrode (ISE)

Most routinely used method for sodium determination.

Diabetes insipidus

Characterized by copious production of dilute urine (3 to 20L/day).

Reference range for serum/plasma sodium

135-145 mmol/L.

Reference range for urine sodium (24h)

40-220 mmol/d, varies with diet.

Causes of dehydration leading to hypernatremia

Not drinking enough fluids, diarrhea, kidney dysfunction, diuretics, excessive sweating, hormonal imbalance.

Cerebrospinal Fluid

135-150 mmol/L

Hypernatremia Classification by Urine Osmolality

< 300 mOsm/kg

Hypernatremia Classification by Urine Osmolality

300-700 mOsm/kg

Hypernatremia Classification by Urine Osmolality

> 700 mOsm/kg

Potassium

Major intracellular cation

Potassium

Mainly from fruits and vegetables

Potassium

Has a blood pressure-lowering effect

Potassium Functions

Regulation of neuromuscular excitability

Potassium Functions

Contraction of the heart

Potassium Functions

ICF volume

Potassium Functions

H+ concentration

Plasma K+ Effect

Affects the resting membrane potential (RMP) of the cell (RM is closer to zero), thereby affecting cell excitability

Potassium Sources

Obtained from food and drink and loses it primarily in urine, some in the digestive tract and sweat

Potassium and Muscle Contraction

For muscle contraction, particularly of the heart muscles

Potassium Chloride Use

Typically used in death penalty cases to induce heart arrhythmia

Potassium Regulation

Dietary deficiency or excess is rarely a primary cause of hypo-/hyperkalemia; instead, it enhances the degree of the disorder → cause is mostly due to a preexisting condition

Symptoms of Potassium Imbalance

Usually involve the CNS

Symptoms of Potassium Imbalance

Altered mental status

Symptoms of Potassium Imbalance

Lethargy

Symptoms of Potassium Imbalance

Irritability

Symptoms of Potassium Imbalance

Restlessness

Symptoms of Potassium Imbalance

Seizures

Symptoms of Potassium Imbalance

Muscle twitching

Symptoms of Potassium Imbalance

Hyperreflexia

Symptoms of Potassium Imbalance

Fever

Symptoms of Potassium Imbalance

Nausea or vomiting

Symptoms of Potassium Imbalance

Difficult respirations

Symptoms of Potassium Imbalance

Increased thirst

Aldosterone

Hormone produced by the adrenal glands in the kidneys that mainly controls levels.

K+ Loss

Occurs whenever the Na+, K+-ATPase pump is inhibited by conditions such as hypoxia, hypomagnesemia, or digoxin overdose.

Digoxin

A drug used in the pediatric population with heart failure or reduced pumping ability to stimulate the heart.

Insulin

Promotes acute entry of K+ into skeletal muscle and liver by increasing Na+, K+-ATPase activity; used in hyperkalemia.

Catecholamines

Such as epinephrine (β2-stimulator), promote cellular entry of K+.

Propranolol

A β-blocker that impairs cellular entry of K+.

Exercise

Causes K+ release from muscle cells, reversible after several minutes of rest.

Hypernatremia

Must be corrected gradually; too rapid correction can induce cerebral edema and death.