Methods of Glucose measurement Flashcards

1
Q

Specimen considerations for glucose measurement to prevent glycolysis

A

Use of NaF or SST

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2
Q

Rate of glycolysis at room temperature if not prevented

A

7 mg/dL/h

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3
Q

Rate of glycolysis at 4°C if not prevented

A

2 mg/dL/h

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4
Q

Effect of 10% contamination with 5% dextrose

A

Artificially elevates glucose levels

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5
Q

Initial reaction of chemical glucose methods

A

Alkaline copper titrate (Benedict’s method)

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6
Q

Reaction involved in Folin-Wu method

A

Cu+ + phosphomolybdic acid → phosphomolybdenum (blue color)

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7
Q

Reaction involved in Nelson-Somogyi method

A

Cu+ + arsenomolybdic acid → arsenomolybdenum

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8
Q

Reaction involved in Neocuproine method

A

Cu+ + neocuproine → Cu-neocuproine complex (yellow/yellow-orange color)

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9
Q

Principle of Ferric Reduction (Hagedorn-Jensen method)

A

Ferricyanide (yellow-orange) reduced to ferrocyanide (colorless) by glucose

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10
Q

Reaction in condensation method (Dubowski method)

A

Glucose + o-toluidine → Schiff’s base (green color)

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11
Q

Glucose oxidase reaction in enzymatic method

A

β-D-glucose + O2 + H2O → Gluconic acid + H2O2

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12
Q

Detection method for glucose oxidase

A

Peroxidase-coupled (Trinder reaction)

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13
Q

End product of glucose oxidase detection (Trinder reaction)

A

Oxidized chromogen (quinonimine; red/red-purple) + H2O

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14
Q

Interference causing false increased glucose in Trinder reaction

A

Oxidizers

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15
Q

Interference causing false decreased glucose in Trinder reaction

A

Reducing agents (drug metabolites, ascorbic acid, ketoacids)

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16
Q

Polarographic method measures

A

Degree of O2 consumption using a pO2 Clark electrode

17
Q

Substances required in polarographic methods (MICE)

A

Molybdate, Iodate, Catalase, Ethanol

18
Q

Hexokinase reaction for glucose measurement

A

Glucose + ATP → Glucose-6-PO4 + ADP

19
Q

Coupling reaction in hexokinase method

A

Glucose-6-PO4 + NADP → 6-phosphogluconolactone + NADPH

20
Q

Detection of hexokinase reaction

A

Increased absorbance at 340 nm (NADPH)

21
Q

Interference in hexokinase method

A

Hemolyzed/icteric samples cause false decreased glucose estimate

22
Q

Glucose dehydrogenase reaction

A

Glucose + NAD → Gluconolactone + NADH + H+

23
Q

Alternative detection for glucose dehydrogenase method

A

NADH + tetrazolium dye → formazan blue (colorimetric-spectrophotometric measurement)

24
Q

Specificity of glucose dehydrogenase method

A

Highly specific for glucose, not subject to interference from substances in serum

25
Application of glucose dehydrogenase method
Primarily used in POCT devices (glucometers)
26
Reference method for glucose measurement
Hexokinase (UV method)
27
UV absorbance wavelength for glucose dehydrogenase/hexokinase
340 nm
28
Advantage of glucose dehydrogenase
Not subject to common interferences, highly specific