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Clinical Biochem > ISE and Electrolytes > Flashcards

ISE and Electrolytes Flashcards

1
Q

Sodium reference range

A

133-146 mmol/L
critical: <125 or >155 mmol/L

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2
Q

Potassium reference range

A

3.5-5.0 mmol/L
critical: <2.6 or >6.2 mmol/L

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3
Q

Chloride reference range

A

96-109 mmol/L

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4
Q

Bicarbonate reference range

A

23-31 mmol/L

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5
Q

Calcium reference range

A

2.10-2.60 mmol/L
critical: <1.65 or >3.25 mmol/L

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6
Q

Magnesium reference range

A

0.70-1.00 mmol/L
critical: <0.40 or >1.90 mmol/L

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7
Q

Phosphorus reference range

A

0.80-1.45 mmol/L
critical: <0.40

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8
Q

Anion gap reference range

A

4-16 mmol/L

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9
Q

Osmolality (serum) reference range

A

280-300 mmol/Kg

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10
Q

Osmol gap reference range

A

<10 mmol/L

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11
Q

Activity

A

the proper term for the concentration of an electrolyte measured in an electrochemical cell used in the Nernst equation

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12
Q

Activity Coefficient

A

the activity of an electrolyte divided by molar concentration, a measurement of the interaction of the selected electrolytes with other species in the solution

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13
Q

Potentiometry

A

an electrochemical technique that measures the electric potential between two electrodes under equilibrium conditions

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14
Q

Potentiometric electrode

A

consists of a reference electrode and an indicator electrode

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15
Q

Reference electrode

A

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

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16
Q

Indicator electrode

A

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

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17
Q

Nernst equation

A

Ecell=Eind-Eref + Ejxn

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18
Q

Classes of ion-selective membranes

A

glass, liquid/polymer, solid state, gas sensing

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19
Q

Glass membranes

A

used to measure H and Na
commonly composed of SiO2, Na2O, CaO or Al2O3

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20
Q

Liquid/Polymer membranes

A

composed of an ion exchanger or ionophore (lipophilic) dissolved in a viscous, water insoluble solvent

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21
Q

Solid state membranes

A

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

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22
Q

Gas permeable membranes

A

has a thin outer membrane that is permeable to the gas of interest and an internal pH electrode

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23
Q

What are limitations to ISE

A

temperature, ionic strength, pH, biofouling, cross-reacting ions, electrolyte exclusion effect

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24
Q

What is the electrolyte exclusion effect

A

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)

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25
Q

pH ISE

A

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

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26
Q

Sodium ISE

A

composed of glass or PVC with crown ether

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27
Q

Preferred specimen for sodium ISE

A

serum or heparin plasma

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28
Q

Interferences with sodium ISE

A

hyperlipidemia (false decrease if indirect ISE)
hyperproteinemia

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29
Q

Potassium ISE

A

composed of PVC and valinomycin or polymers containing crown ether bis heptanedioate

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30
Q

Preferred specimen for potassium ISE

A

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

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31
Q

Interferences for potassium ISE

A

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

32
Q

Chloride ISE

A

composed of polymer and incorporated quaternary ammonium salt anion exchanges

33
Q

Preferred specimen for chloride ISE

A

serum or lithium heparin

34
Q

Interferences for chloride ISE

A

may lack selectivity in the presence of other halides and organic ions (thiocyanate/lactate)

35
Q

Carbon dioxide ISE

A

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

36
Q

Preferred specimen for carbon dioxide ISE

A

arterial heparinized blood, serum or plasma

37
Q

Interferences for carbon dioxide ISE

A

exposure to atmospheric air decreases CO2
build up of protein on the ISE membrane will cause errors
temperature, barometric pressure and erroneous calibration

38
Q

Bicarbonate testing

A

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

39
Q

Preferred specimen for bicarbonate testing

A

serum or lithium heparin whole blood or plasma

40
Q

Interferences in bicarbonate testing

A

CO2 will decrease if exposed to atmospheric air

41
Q

Calcium ISE

A

consists of a calcium ionophore membrane case on a solid support, measures ionized calcium

42
Q

Preferred sample for calcium ISE

A

collect anaerobically, dry heparin, maintain temperature at 4C, avoid fist pumping as it will cause blood pH to decrease and ionize calcium

43
Q

Interferences of calcium ISE

A

ethanol, proteins, phosphate, lactate

44
Q

Calcium O-Cresolphthalein testing

A

calcium is freed from albumin via acidification, then under alkaline conditions calcium binds to O-Cresolphthalein causing a colour change

45
Q

Preferred specimen for Calcium O-Cresolphthalein testing

A

serum or lithium heparin plasma

46
Q

Interferences for Calcium O-Cresolphthalein testing

A

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

47
Q

Phosphorus testing

A

inorganic phosphorus binds to ammonium molybdate in acidic solution to form a complex measured at 340 nm

48
Q

Preferred specimen for phosphorus testing

A

serum of lithium heparin
in unseparated specimens phosphate can increase upon storage at RT of 37C

49
Q

Interferences of phosphorus testing

A

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

50
Q

Magnesium testing

A

magnesium binds to calmagite to form a stable chromogen which is measured at 532nm

51
Q

Preferred sample for magnesium testing

A

serum of lithium heparin plasma

52
Q

Interferences in magnesium testing

A

hemolysis, bilirubin, lipemia
EDTA, potassium oxalate, sodium citrate
EGTA can be used to decrease calcium interferences

53
Q

Anion gap

A

the gap between measured cations and anion, due to unmeasured anions such as proteins, sulphates and phosphates

54
Q

Anion gap equation

A

Na - (Cl - HCO3)

55
Q

What causes increased anion gap

A

diabetic ketoacidosis, lactic acidosis, renal failure, renal tubular necrosis, diarrhea, decreased reabsorption of bicarbonate, intoxication with organic compounds (ethanol, methanol or ethylene glycol)

56
Q

What causes decreased anion gap

A

hypoalbuminemia, hypercalcemia, hypermagnesemia or hypergammaglobulinemia

57
Q

What regulates sodium

A

renal angiotensin aldosterone system (kidney)

58
Q

What causes hypernatremia

A

primary aldosteronism, cushings syndrome, secondary aldosteronism, damage to the hypothalamus (causing decreased thirst), diabetes insipidus

59
Q

What causes hyponatremia

A

(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

60
Q

What regulates chloride

A

renin angiotensin aldosterone system (kidney)
excess is found in sweat and excreted in urine

61
Q

What causes hyperchloremia

A

similar to hypernatremia
respiratory alkalosis where HCO3 is excreted alongside Na rather than ClWa

62
Q

What causes hypochloremia

A

similar to hyponatremia
furosemide inhibits Cl reabsorption in the kidneys

63
Q

What regulates potassium

A

the kidneys, aldosterone and insulin

64
Q

What causes hyperkalemia

A

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

65
Q

What causes hypokalemia

A

redistribution can cause due to insulin therapy and alkalosis
renal tubular acidosis, tubular necrosis, corticoid hormone excess with metabolic acidosis
decreased intake
excessive loss

66
Q

What regulates bicarbonate

A

kidneys and lungs

67
Q

What regulates calcium

A

Parathyroid hormone, PTH, Calcitriol (synthesized from vitamin D)

68
Q

What causes hypercalcemia

A

primary hyperparathyroidism
malignancy (breast cancer)
tumours that invade bone and stimulate reabsorption
renal failure and endocrine disorders

69
Q

What causes hypocalcemia

A

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

70
Q

What regulates phosphate

A

parathyroid hormone and calcitriol

71
Q

What causes hyperphosphatemia

A

hyperparathyroidism
pseudohypoparathyroidism
acromegaly

72
Q

What cause hypophosphatemia

A

a shift from ECF to ICF due to respiratory alkalosis, glucose administration or insulin
renal wasting
hyperparathyroidism, Fanconis syndrome, inherited rickets, osteomalacia

73
Q

What regulates magnesium

A

no specific mechanism

74
Q

What causes hypermagnesemia

A

excessive administration of antacids, enemas and fluids containing magnesium

75
Q

What causes hypomagnesemia

A

shift from ECF to ICF
intestinal origin (diarrhea, vomiting, bowel surgery)
kidney origin (diabetes mellitus, diuretics, antibiotics, alcoholism)

Clinical Biochem (8 decks)

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