ISE and Electrolytes Flashcards
Sodium reference range
133-146 mmol/L
critical: <125 or >155 mmol/L
Potassium reference range
3.5-5.0 mmol/L
critical: <2.6 or >6.2 mmol/L
Chloride reference range
96-109 mmol/L
Bicarbonate reference range
23-31 mmol/L
Calcium reference range
2.10-2.60 mmol/L
critical: <1.65 or >3.25 mmol/L
Magnesium reference range
0.70-1.00 mmol/L
critical: <0.40 or >1.90 mmol/L
Phosphorus reference range
0.80-1.45 mmol/L
critical: <0.40
Anion gap reference range
4-16 mmol/L
Osmolality (serum) reference range
280-300 mmol/Kg
Osmol gap reference range
<10 mmol/L
Activity
the proper term for the concentration of an electrolyte measured in an electrochemical cell used in the Nernst equation
Activity Coefficient
the activity of an electrolyte divided by molar concentration, a measurement of the interaction of the selected electrolytes with other species in the solution
Potentiometry
an electrochemical technique that measures the electric potential between two electrodes under equilibrium conditions
Potentiometric electrode
consists of a reference electrode and an indicator electrode
Reference electrode
stable and has a constant potential relative to the sample solution, has a junction to allow electrical ionic conductivity between the sample solution and the internal filling solution
Indicator electrode
has an ion selective membrane where a potential difference occurs when there is a difference in the activity of ions on either side of the membrane
Nernst equation
Ecell=Eind-Eref + Ejxn
Classes of ion-selective membranes
glass, liquid/polymer, solid state, gas sensing
Glass membranes
used to measure H and Na
commonly composed of SiO2, Na2O, CaO or Al2O3
Liquid/Polymer membranes
composed of an ion exchanger or ionophore (lipophilic) dissolved in a viscous, water insoluble solvent
Solid state membranes
composed of a single type of crustal or pressed pellet of salts of the ion of interest
membrane potential is created by the movement of ions from the sample into vacancies in the crystal lattice
Gas permeable membranes
has a thin outer membrane that is permeable to the gas of interest and an internal pH electrode
What are limitations to ISE
temperature, ionic strength, pH, biofouling, cross-reacting ions, electrolyte exclusion effect
What is the electrolyte exclusion effect
indirect ISEs dilute the patients sample with an aqueous solution. Sodium levels will by falsely low in samples that have a high solid proportion (ie. hyperlipidemia or hyperproteinemia)
pH ISE
composed of glass, ion exchange between sodium and hydrogen occurs altering the potential of the electrode which correlates with hydrogen ion activity
temperature dependent, if temperature increases, pH decreases
exposure to atmospheric air will decrease CO2 and increase pH
Sodium ISE
composed of glass or PVC with crown ether
Preferred specimen for sodium ISE
serum or heparin plasma
Interferences with sodium ISE
hyperlipidemia (false decrease if indirect ISE)
hyperproteinemia
Potassium ISE
composed of PVC and valinomycin or polymers containing crown ether bis heptanedioate
Preferred specimen for potassium ISE
separated serum or heparin plasma
at 4C potassium will increase in unseparated samples due to leakage from RBCs
at RT or 37C potassium can decrease due to glycolysis
serum samples have higher potassium than plasma because platelets release potassium during clotting
Interferences for potassium ISE
hemolysis
incorrect torniquet use may falsely increase
excessive fist clenching or forearm exercise may falsely increase
leukocytosis may falsely increase if not immediately separated
thrombocytosis may falsely increase
Chloride ISE
composed of polymer and incorporated quaternary ammonium salt anion exchanges
Preferred specimen for chloride ISE
serum or lithium heparin
Interferences for chloride ISE
may lack selectivity in the presence of other halides and organic ions (thiocyanate/lactate)
Carbon dioxide ISE
composed of teflon or silicone, carbon dioxide passe through the membrane and dissolves within an inner electrolyte solution, ions are detected by an interior pH ISE
Preferred specimen for carbon dioxide ISE
arterial heparinized blood, serum or plasma
Interferences for carbon dioxide ISE
exposure to atmospheric air decreases CO2
build up of protein on the ISE membrane will cause errors
temperature, barometric pressure and erroneous calibration
Bicarbonate testing
carbon dioxide and carbonic acid are converted to bicarbonate by an alkaline pH, it goes through a series of reactions and then NAD production is measured spectrophotemetrically
Preferred specimen for bicarbonate testing
serum or lithium heparin whole blood or plasma
Interferences in bicarbonate testing
CO2 will decrease if exposed to atmospheric air
Calcium ISE
consists of a calcium ionophore membrane case on a solid support, measures ionized calcium
Preferred sample for calcium ISE
collect anaerobically, dry heparin, maintain temperature at 4C, avoid fist pumping as it will cause blood pH to decrease and ionize calcium
Interferences of calcium ISE
ethanol, proteins, phosphate, lactate
Calcium O-Cresolphthalein testing
calcium is freed from albumin via acidification, then under alkaline conditions calcium binds to O-Cresolphthalein causing a colour change
Preferred specimen for Calcium O-Cresolphthalein testing
serum or lithium heparin plasma
Interferences for Calcium O-Cresolphthalein testing
hemolysis (EGTA can be added to dissociate complex, any colour left will be due to hemolysis and can be accounted for), icterus, lipemia, magnesium ions (reduced by addition of 8-hydroxyquinoline and at pH 12 and read at 570-580nm), gadolinium compounds and paraproteins
Phosphorus testing
inorganic phosphorus binds to ammonium molybdate in acidic solution to form a complex measured at 340 nm
Preferred specimen for phosphorus testing
serum of lithium heparin
in unseparated specimens phosphate can increase upon storage at RT of 37C
Interferences of phosphorus testing
hemolysis, icterus, lipemia
EDTA, citrate and oxalate
monoclonal free light chains
complex can be reduces with naphthol sulfonic acid and measured at 600-700nm to reduce interferences at 340nm
Magnesium testing
magnesium binds to calmagite to form a stable chromogen which is measured at 532nm
Preferred sample for magnesium testing
serum of lithium heparin plasma
Interferences in magnesium testing
hemolysis, bilirubin, lipemia
EDTA, potassium oxalate, sodium citrate
EGTA can be used to decrease calcium interferences
Anion gap
the gap between measured cations and anion, due to unmeasured anions such as proteins, sulphates and phosphates
Anion gap equation
Na - (Cl - HCO3)
What causes increased anion gap
diabetic ketoacidosis, lactic acidosis, renal failure, renal tubular necrosis, diarrhea, decreased reabsorption of bicarbonate, intoxication with organic compounds (ethanol, methanol or ethylene glycol)
What causes decreased anion gap
hypoalbuminemia, hypercalcemia, hypermagnesemia or hypergammaglobulinemia
What regulates sodium
renal angiotensin aldosterone system (kidney)
What causes hypernatremia
primary aldosteronism, cushings syndrome, secondary aldosteronism, damage to the hypothalamus (causing decreased thirst), diabetes insipidus
What causes hyponatremia
(normal osmolality) electrolyte exclusion effect
(high osmolality) hyperglycemia, uremia or mannitol
(low osmolality) liver, kidney or heart disease, SIADH, Addisons disease, diuretics, extrarenal fluid loss
What regulates chloride
renin angiotensin aldosterone system (kidney)
excess is found in sweat and excreted in urine
What causes hyperchloremia
similar to hypernatremia
respiratory alkalosis where HCO3 is excreted alongside Na rather than ClWa
What causes hypochloremia
similar to hyponatremia
furosemide inhibits Cl reabsorption in the kidneys
What regulates potassium
the kidneys, aldosterone and insulin
What causes hyperkalemia
preanalytical variables cause pseudohyperkalemia (hemolysis, thrombocytosis, leukocytosis)
redistribution occurs during acidosis, IVH, rhabdomyolysis, burns and tissue hypoxia
increased retention due to Addisons disease, hypoaldosteronism and treatment with ACE inhibitors
What causes hypokalemia
redistribution can cause due to insulin therapy and alkalosis
renal tubular acidosis, tubular necrosis, corticoid hormone excess with metabolic acidosis
decreased intake
excessive loss
What regulates bicarbonate
kidneys and lungs
What regulates calcium
Parathyroid hormone, PTH, Calcitriol (synthesized from vitamin D)
What causes hypercalcemia
primary hyperparathyroidism
malignancy (breast cancer)
tumours that invade bone and stimulate reabsorption
renal failure and endocrine disorders
What causes hypocalcemia
hypoalbuminemia
lower total calcium levels with normal free calcium
liver, renal and heart disease
chronic renal failure
proteinuria resulting in hypoalbuminemia
hyperphosphatemia
hypoparathyroidism
neck surgery that destroys the parathyroid gland
What regulates phosphate
parathyroid hormone and calcitriol
What causes hyperphosphatemia
hyperparathyroidism
pseudohypoparathyroidism
acromegaly
What cause hypophosphatemia
a shift from ECF to ICF due to respiratory alkalosis, glucose administration or insulin
renal wasting
hyperparathyroidism, Fanconis syndrome, inherited rickets, osteomalacia
What regulates magnesium
no specific mechanism
What causes hypermagnesemia
excessive administration of antacids, enemas and fluids containing magnesium
What causes hypomagnesemia
shift from ECF to ICF
intestinal origin (diarrhea, vomiting, bowel surgery)
kidney origin (diabetes mellitus, diuretics, antibiotics, alcoholism)