Module 3- Electrolytes Flashcards
What are the functions of electrolytes?
Maintenance of osmotic pressure, water balance, pH, enzyme cofactors/activators
Regulation of heart and muscle
What should you avoid when collecting electrolytes?
Hemolysis
Proper anticoagulant (not K3EDTA tubes)
Separation from cells (increases K)
K can increase after exercise or clenching fist
What are electrolytes?
Molecules that dissociate into charged ions
In lab, we refer to:
Na, K, Cl, HCO3
How is water distributed?
Intracellular - 70%
Extracellular - 30%
- plasma 20%
- interstital fluid 80%
What is concentrated state vs. diluted state?
Concentrated - hypernatremia, hyperosmolality, hypovolemia- needs more water
Diluted - hyponatremia, hyposomolality, hypervolemia - need less water
What is ADH?
Released from posterior pituitary in response to high osmolality. Acts on kidney tubules to increase water reabsorption.
What is aldosterone?
Released from the adrenal gland in response to low sodium/osmolality. Acts on kidney tubules to increase reabsorption of sodium.
What is sodium and how it is regulated?
Extracellular
Role in plasma osmolality and water balance
Reabsorbed in tubules
Regulated by aldosterone
What is potassium? How is it regulated?
Intracellular
Reabsorbed in proximal tubules
Regulates cell membrane potential
Regulated by aldosterone (reabsorption of Na means secretion of K)
Levels affected by dehydration, acidosis, alkalosis, and cellular breakdown
What is chloride? What is anion gap?
Extracellular
Reabsorbed by tubules passively
Maintains electroneutrality
Anion gap= cations - anions
Ref range: 5-15 mmol/L
Ref range with K: 10-20 mmol/L
Gap is due to anions present in sample that are not measured
What does it indicate when anion gap is increased? Decreased? Negative?
Increased - displacement of Cl-
Decreased - rare
Negative - indicates a issue, check sample and repeat
What is bicarbonate?
The form most CO2 is transported in the plasma
What is magnesium?
Intracellular
Functions in enzyme activation, nerve conductivity, neuromuscular contraction, formation of bones and teeth
Ionized form in plasma is the active form
Regulated by PTH
What is calcium? How is it regulated?
99% bones and teeth In plasma: - 50% free ionized active form - 45% protein bound - 5% in complexes
Regulated by PTH (if levels are low) and calcitonin (if levels are high)
What does it indicate if calcium levels are high? Low?
High - hypercalcemia, Muscle weakness, cardiac arrhythmias
Low - hypocalcemia, increased muscle excitability. May be low with high protein levels and high pH levels
Calcium and phosphate levels tend to act inversely
What is the role of calcium?
Enzyme activation
Muscle contraction
Membrane permeability
Cell motility
What is phosphorus and how is it regulated?
Intracellular
Most contained in bone
Regulated by PTH, Vit D, and GH
What is fluid depletion?
Caused by: Excessive vomiting Decreased water intake Polyuria High temperature
Dehydration - blood has increased Na, increased plasma osmolality, increased Hct, increased urea
Urine has decreased volume
What is diabetes insipidus?
Decreased ADH, causes less water to be absorbed in kidney tubules
Failure to concentrate urine
Urine will have low specific gravity and no glucose
What is fluid excess?
Homeostatic imbalance
increased intake
Increased ADH
Can lead to edema (build up of fluid causing swelling)
Sodium disorders - hypernatremia
Decreased plasma water
Increased plasma sodium
Dehydration
Hyperaldosteroneism
Sodium disorders - hyponatremia
Inappropriate ADH secretion
Hypoaldosteronism Addison’s disease
What is the electrolyte exclusion effect?
Pseudo hyponatremia
Hyperlipidemia - excess solids reduces the plasma component in blood
(Electrolytes only dissolved in the plasma)
There is a decrease in ALL electrolyte levels when using indirect methods
Potassium disorders - hyperkalemia
Caused by crush injuries, trauma
Metabolic acidosis - decreased pH, plasma K increases
Hypoaldosteronism/Addison’s disease - decreased aldosterone, less K excreted
Potassium disorders - hypokalemia
Hyperaldosteronism - increased K excretion
Metabolic alkalosis
Prolonged vomiting or diarrhea
Chloride disorders - hypochloremia
Displacement by other anions
Associated with Na losses
Chloride disorders - hyperchloremia
Dehydration
Increased salt intake
Decreased bicarbonate levels
What is sweat chloride?
Aids in the diagnosis of cystic fibrosis
Autosomal recessive trait of sweat gland excretion
Sweat chloride will be markedly elevated
Magnesium disorders - hypermagnesemia
From administration of magnesium containing products
Renal failure
Magnesium disorders - hypomagnesemia
Prolonged vomiting or diarrhea
Malnutrition
Calcium disorders - hypercalcemia
Hyperparathyroidism
Malignancies
Excessive vitamin D
Multiple myeloma
Calcium disorders - hypocalcemia
Hypoparathyroidism
Protein loss
Chronic hypomagnesemia
Phosphorous disorders - hyperphosphatemia
Acute or chronic renal failure
Increased intake
Lymphoblastic leukemias
Phosphorous disorders - hypophosphatemia
Hyperparathyroidism
Long term total parenteral nutrition
Sodium analysis:
Ion selective electrode - glass membrane
Interference from hemolysis, lipid/proteinemia
What is the reference range for sodium?
Serum/plasma 135-150 mmol/L
Potassium analysis:
Ion selective electrode - valinomycin electrode
Interference from: hemolysis, time on cells, lipid/proteinemia
What is the reference range for potassium?
Serum/plasma: 3.5-5.0 mmol/L
Chloride analysis:
Coulometric titration - silver ions present in excess which causes a change in conductivity
ISE - silver chloride/silver sulphide membrane electrode
Mercuric thiocyanate (photometrically) 480nm
Interference from bromide and lipid/proteinemia
What is the reference range for chloride?
Serum/plasma 98-108 mmol/L
Bicarbonate analysis:
ISE - silicone rubber membrane with pH electrode
Ref range 22-30 mmol/L
Magnesium analysis:
Spectrophotometric
Interference from hemolysis, time in cells, tourniquet use, EDTA citrate or oxalate anticoagulants
Ref range 0.65-1.05 mmol/L
Calcium analysis:
Spectrophotometric
ISE from ionized Ca
Interference from EDTA, citrate or oxalate anticoagulants, patient position, time on cells, ionized calcium should be tested immediately
Ref ranges
Total calcium 2.10-2.60 mmol/L, CL 3.25
Ionized calcium 1.15-1.35 mmol/L, CL 1.50
Phosphorous analysis:
Spectrophotometric
Interference from hemolysis, time in cells, EDTA oxalate or citrate anticoagulants
Ref ranges 0.80-1.50 mmol/L
