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• Electrolytes 3 covers Chloride, and Electrolytes 4 covers Calcium, Magnesium, Phosphate.

Chloride

• Most abundant extracellular anion.
• More concentrated in the extracellular fluid (ECF) than inside the cell.
• Chloride shifts secondary to Na⁺ or HCO₃⁻.
• Reabsorbed along with Na⁺ in the kidney to maintain electroneutrality.
• Moves into red blood cells (RBCs) to balance HCO₃⁻ movement out of RBCs.

Chloride Shift

• Carbon dioxide (CO₂) from cellular metabolism diffuses into plasma and RBCs.
• In RBCs, CO₂ combines with H₂O to form H₂CO₃, dissociating into H⁺ and HCO₃⁻.
• HCO₃⁻ moves out of the cell.
• To maintain electroneutrality, Cl⁻ moves into the cell.
• Helps maintain electroneutrality.

Regulation of Chloride

• Some filtered Cl⁻ is reabsorbed, secondary to Na⁺ reabsorption.
• Excess Cl⁻ is excreted in urine and sweat.

Chloride Reference Range

• Serum/Plasma Chloride normal range: 98-107 mmol/L.
• Critical Values: Less than 70 or greater than 120 mmol/L.

Hypochloremia

• Low serum/plasma Cl⁻ levels = Cl⁻ < 98 mmol/L.
• Often results from conditions causing decreased Na⁺ levels.
• Can be caused by Hypoaldosteronism, Diuretics, GI loss of Cl⁻, and Metabolic Alkalosis.

Hyperchloremia

• High serum/plasma Cl⁻ levels = Cl⁻ > 107 mmol/L.
• Caused by conditions increasing Na⁺ levels, excessive Cl⁻ intake, Renal Tubular Acidosis, and Metabolic Acidosis.

Chloride Specimens

• Type of sample: Serum, Plasma, Whole Blood, or Urine.
• Lithium Heparin can be used.
• Do Not use hemolyzed sample.
• Not affected by intracellular chloride itself but have dilutional effect.
• Can also be run on sweat.

Cystic Fibrosis and Chloride

• Autosomal recessive inherited disease affects exocrine glands and cause electrolyte and mucous secretion abnormalities.
• Can cause pneumonia and pancreatic insufficiency, secondary to heavy mucous secretions.
• More common in Caucasian population

Chloride Methods

• Current Method: Ion-Selective Electrode (ISE)
• The electrode used for Cl⁻ is Ag-Cl.

Sweat Chloride Analysis

• Analysis is used for Cystic Fibrosis diagnosis.
• Pilocarpine stimulates sweat glands for collection.
• Sweat is absorbed onto a gauze pad via iontophoresis.
• A positive test for CF = >60 mmol/L, and it is confirmed with a second test.

Bicarbonate

• Second most abundant extracellular anion.
• More concentrated in the ECF than inside the cell.
• Total CO₂ = HCO₃⁻ + H₂CO₃ + pCO₂ (partial/dissolved).
• Bicarbonate (HCO₃⁻) accounts for over 90% of total CO₂ and total CO₂ is used as a measurement of HCO₃⁻.

Bicarbonate Maintenance

• Bicarbonate moves out of RBCs to maintain pH.
• Balanced by Cl⁻ movement into RBCs.

Bicarbonate Buffer System

• CO₂ from cellular metabolism diffuses into plasma and RBCs.
• In RBCs, CO₂ combines with H₂O to form H₂CO₃ (carbonic acid).
  • Helps prevent toxic CO₂ build-up.
  • Catalyzed in either direction by carbonic anhydrase.
• H₂CO₃ dissociates into H⁺ and HCO₃⁻.
• CO₂ + H₂O ⇄ H₂CO₃ ⇄ H⁺ + HCO₃⁻
• HCO₃⁻ moves out of the cell.
  • Can act as a buffer to combine with excess H⁺ in plasma.
• To maintain electroneutrality, Cl⁻ moves into the cell.
• HCO₃⁻ and H⁺ in plasma form H₂O and CO₂, which is eliminated via the lungs.

Bicarbonate Function and Regulation

• Temporary storage form of CO₂ until it can be eliminated.
• Helps to maintain pH (buffer).
• Filtered as HCO₃⁻, converts to H₂O and CO₂ in tubules.
• Reabsorbed as CO₂, it converts back to HCO₃⁻ in plasma.

Bicarbonate Reference Ranges

• Serum/Plasma Total CO₂: 22-33 mmol/L.
• Acidosis = low HCO₃⁻ levels compared to pCO₂ (Decreased HCO₃⁻: < 22).
• Alkalosis = high HCO₃⁻ levels compared to pCO₂ (Increased HCO₃⁻: > 33 mmol/L).

Bicarbonate Specimens

• Type of sample: Serum or Plasma and Whole Blood.
• Lithium Heparin can be used.
• Separate plasma from cells immediately.
• Analyze immediately once uncapped to prevent CO₂ loss.

Common Bicarbonate Methods

• Ion-Selective Electrode (ISE).
• Acid is used to convert all forms of CO₂ to gas (pCO₂).
• Electrode used for CO₂: pH electrode.

Enzymatic Method

• Alkalinized to convert all forms of CO₂ to HCO₃⁻.
• Catalyze the reaction: HCO₃⁻ → Oxaloacetate + NADH → Malate + NAD⁺.
• Increased HCO₃⁻ = decreased NADH = decreased Absorbance at 340 nm.

Calcium

• Calcium is found in bone (99%) which acts as storage for Ca²⁺, Mg²⁺, and PO₄³⁻ ECF and ICF.
• Calcium is more concentrated in the ECF than inside the cell

Calcium Forms

• Free ionized Ca²⁺ (45%) is the biologically active form.
• Protein-bound calcium is mostly bound to albumin.
• Ionized Ca²⁺ is closely maintained and critical for proper muscle contractility, but albumin changes do not affect ionized Ca²⁺.
• Total Ca²⁺ can change with changes in albumin and bound-ions.
• Total Ca²+ is not a reliable measure of ionized Ca²⁺, especially in acutely ill individuals.

Calcium Functions

• Maintenance of muscle contractility
• Bone and teeth formation
• Nerve Impulse transmission
• Coagulation and enzyme activation.

Calcium Reference Range

-Serum/Plasma Calcium normal range: 8.5-10.5 mg/dL -Serum Ionized Calcium normal range: 4.6-5.3 mg/dL

Calcium Regulation

• Non Bound Ca²⁺ enters the filtrate

Parathyroid Hormone

• A decrease in ionized Ca²⁺ stimulates secretion from the parathyroid gland.
• Increases bone resorption, kidney reabsorption, kidney production of Vitamin D, and absorption in the intestine.

Vitamin D

• A decrease in ionized Ca²⁺ stimulates PTH secretion, which stimulates renal production of Vitamin D.
• Increases absorption in the intestine and kidney reabsorption, and enhances bone resorption.

Calcitonin

• A significant Increase in ionized Ca²⁺ stimulates release from the thyroid gland.
• Blocks bone resorption, decreases intestinal absorption, and decreases kidney reabsorption.

Hypocalcemia

• Low serum/plasma Ca²⁺ levels: Ca²⁺ < 8.5 mg/dL.

Causes of Hypocalcemia

• Hypoparathyroidism
• Vitamin D Deficiency
• Hypoalbuminemia
• Renal Disease.
• Symptoms: Neuromuscular and Cardiac Arrhythmia.

Hypercalcemia

• High serum/plasma Ca²⁺ levels: Ca²⁺ > 10.5 mg/dL.

Causes of Hypercalcemia

• Hyperparathyroidism
• Vitamin D Excess
• Milk-Alkali Syndrome
• Malignancy
• Symptoms: Neuromuscular, Renal calculi, and GI issues.

Calcium Specimens

• Total Calcium – type of sample: Serum, Plasma, Urine.
• Lithium Heparin (NO EDTA is Chelates Calcium)
• Ionized Calcium – type of sample: Serum, Whole Blood.
• Heparin, collected anaerobically due to CO₂ loss causes increased pH.
• Causes more Ca²⁺ binding to albumin and decrease ionized Ca²⁺.

Ionized and Total Calcium

• Ionized Calcium is of greatest importance compared to Total Calcium.
• Especially important for patients in critical condition (e.g., ICU, Surgery).

Calcium Methods

• Reference Method: Atomic Absorption Spectrophotometry.
• Current Methods: Ion-Selective Electrode (ISE) -Used to measure ionized/free Ca²⁺ -Also measures pH, used to correct calcium to a pH of 7.40 = "normalizing" -Current Methods: Dye-Binding Methods
• Total Ca²⁺ measurement
• Sample is acidified to release all bound Ca2+ All calcium is now in "free" state, complexes: -Orthocresolphthalein Complexone (o-CPC) -Arsenazo III Dye
• Increased Calcium = Increased Dye Complex = Increased Absorbance

Magnesium

• Second most abundant intracellular cation.
• More concentrated inside the cell than ECF.

Where to Find Magnesium

• Bone acts as storage for Ca²⁺, Mg²⁺, and PO₄³⁻.
• Tissue.
• ECF
• RBCs (little).

Magnesium Forms

• The forms are free ionized Mg²⁺ form, protein-bound form, and ion-bound form just like Ca²⁺.

Magnesium Functions

• Cofactor for many enzymes.
• Affects Cardiovascular
• Metabolic
• Neuromuscular functions.

Magnesium Reference Range

• Serum/Plasma Magnesium normal range: 1.7-2.4 mg/dL.

Regulation of Magnesium

• Non-protein bound Mg²⁺ enters the filtrate.
• Parathyroid Hormone (PTH) increases kidney reabsorption and intestinal absorption.

Hypomagnesemia

• Low serum/plasma Mg²⁺ levels: Mg²⁺ < 1.7 mg/dL.
• Symptoms: Neuromuscular, Cardiac Arrhythmia, Psychiatric.

Hypermagnesemia

• Highserum/plasma Mg²⁺ levels: Mg²⁺ > 2.4 mg/dL.
• Symptoms: Neuromuscular, Cardiac (Bradycardia), GI, Skin (Flushing).

Specimen Requirements for magesium samples

• The sample for Total Magnesium: Serum
• Plasma
• Urine
• Lithium Heparin may be used
• NO Hemolysis and Remove serum or plasma from cells immediately
• Affected by intracellular Mg²⁺.

Magnesium Methods

• Reference Method: Atomic Absorption Spectrophotometry.
• Current Methods: Mg²⁺ + Calmagite, Formazan Dye, or Methylthymol Blue: -Colored complex = Increased Absorbance
• Increased Mg²⁺ = Increased colored complex = Increased Absorbance

Phosphate

• Most abundant intracellular anion.
• More concentrated inside the cell than ECF.

Storage of Phospate

• Bone acts as storage for Ca²⁺, Mg²⁺, and PO₄³⁻.
• Tissue
• ECF
• RBCs (little).

Forms of Phospate

• Inorganic PO₄³⁻ (25%): includes free and bound.
• Organic PO₄³⁻ is found as constituents in organic molecules.

Functions of Phospate

• A component of organic molecules such as DNA and RNA, Coenzymes, ATP, 2,3-BPG, etc.
• Bone and Teeth formation, Buffer.

Phospate Reference Range

• Serum/Plasma Phosphate normal range: 2.5-4.5 mg/dL.

Phospate Regulation

• Inorganic, non-protein bound PO₄³ enters the filtrate.

Phospate Parathyroid Hormone (PTH)

• Decreases kidney reabsorption, increases excretion.
• Vitamin D increases intestinal absorption and kidney reabsorption.

Phospate Calcitonin

• Decreases kidney reabsorption and increases excretion.
• Low serum/plasma PO₄³ levels is less than 2.5 mg/dL.

Hypophosphatemia

• Causes: Hyperparathyroidism, Vitamin D Deficiency, and Malabsorption. -Hyperparathyroidism: Increased Calcium, Decreased Phosphate, and Increased PTH* -Vitamin D Deficiency: Decreased Calcium*, Decreased Phosphate*, Increased PTH Increased serum/plasma PO₄³ levels is greater than 4.5 mg/dL.

Hyperphosphatemia

• Causes: Hypoparathyroidism and Vitamin D Excess. -Hyperparathyroidism: Decreased Calcium, Increased Phosphate and Decreased PTH* -Vitamin D Excess: Increased Calcium*, Increased Phosphate* and Decreased PTH

Phosphate Specimen Requirements

• Total Phosphate – type of sample: Serum, Plasma, Urine.
• Lithium Heparin.
• NO Hemolysis and Remove serum or plasma from cells immediately.
• Affected by intracellular PO₄.

Phospate Methods

• Fiske and Subbarow Method is at Acidic pH.
• PO₄³ → Phosphomolybdate + Reducing Agent forms to Molybdenum blue.
• Can read Phosphomolybdate OR read further reduced Molybdenum blue.
• Phosphomolybdate and Molybdenum blue have an Increased Absorbance.

Anion Gap

• Electrolyte panel measures: Na+, K+, Cl, and HCO3 (TCO2).
• Anion Gap = the difference between measured anions and cations due to unmeasured anions/cations.

Unmeasured Anions and Cations

• Due to electroneutrality, the charge balance between anions and cations will be equal.
• Measured anions and cations in the calculation
• Unmeasured Anions and Cations include: PO4, Ca2+, Mg2+, lactic acid, methanol, ethanol, ethylene glycol, salicylates, possibly K+

Anion Gap Equations

-Without Potassium: Na - CI - CO2 (add cations, you subtract anions) -With Potassium: Na + K-CI - CO2 Anion Gap reference ranges. -AG without Potassium: 7-16 mmol/L AG with Potassium: 10-20 mmol/L

Increased Anion Gap Causes

• Uremia/Renal Failure, Ketoacidosis, Methanol, Ethanol, Ethylene Glycol Poisoning, Salicylate Poisoning, and Lactic Acidosis
• Decreased Anion Gap include: Hypoalbuminemia