Analytical interferences and physiological limitations of blood glucose meters
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Analytical Interferences and Physiological Limitations of Blood Glucose Meters. Ken Ervin. Package inserts Review articles (partial list) Boren and Clarke Tonyushkina and Nichols Pitkin and Rice Montagnana et al Wahl Dungan Arabadjief and Nichols Heller and Feldman.

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Presentation Transcript

Published information

Package inserts Blood Glucose Meters

Review articles (partial list)

Boren and Clarke

Tonyushkina and Nichols

Pitkin and Rice

Montagnana et al

Wahl

Dungan

Arabadjief and Nichols

Heller and Feldman

Specific articles (partial list)

Kimberly, et al

Fiore and Delanghe

Lyon, et al

Kazmierczak and Catrou

Goudable, et al

Zheng, et al

Vesper, et al

Katelijne and Delanghe

Tang, et al

Published information

Ken Ervin Consulting Services


Package inserts address procedural limitations
Package inserts address “Procedural limitations” Blood Glucose Meters

  • Sample related

    • e.g. Hct, pO2, DKA, HHNK, etc.

  • Endogenous compounds

  • Exogenous compounds

  • Environmental

    • Temperature

    • Humidity

    • Altitude

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The limitations of a product are dependent upon the choice of technology to achieve the design goals.

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Bgm design goals drive the specifications and choice of technology

Accurate and precise of technology to achieve the design goals.

Highly specific

*Stable at room temperature

*Rapid test (use whole blood directly)

*Very easy to use

Small blood volume

*Inexpensive meter

*Cal code strategy

Low cost/test

More recently

No pO2 dependence

No maltose interference

No hematocrit effect

BGM Design GoalsDrive the specifications and choice of technology

Ken Ervin Consulting Services


To meet the specifications, technologies are chosen for the measurement device and its method of production

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Bgm measurement based on combining technologies
BGM measurement based on combining technologies measurement device and its method of production

  • Method of introducing sample to device

    • Most devices now rely on capillary action, sometimes in two directions

  • Method to identify glucose in sample (specificity)

    • Enzymatic reaction (GO, GDH, Hexokinase/G6PDH)

  • Method to quantify glucose

    • Colorimetric

    • Electrochemical

  • Method of calibration

  • Methods to assess performance of the test or correct results

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Interferences and physiological limitations are related to choices of sample type and technology
Interferences and physiological limitations are related to choices of sample type and technology

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Interferences result from
Interferences result from choices of sample type and technology

  • Analyte specificity issues or

  • Sample and environmental influences on the measurement reaction

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Analyte specificity
Analyte specificity choices of sample type and technology

  • Use of enzymes specific for glucose

    • GO

    • GDH

    • Hexokinase/G6PDH

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Sample influences on measurement
Sample influences on measurement choices of sample type and technology

  • Endogenous substances

    • Uric acid

    • Bilirubin

    • Lipemia, Hemolysis

  • Exogenous substances

    • Acetominophen

    • Ascorbate

    • Maltose, Icodextrin metabolites

    • Mannitol

    • Dopamine

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Sample influences
Sample influences choices of sample type and technology

  • DKA, HHNK

    • pH and/or Viscosity

      • Hyperosmolar, flow effects

      • Less water volume to reconstitute reagent

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Environmental influences
Environmental influences choices of sample type and technology

  • Analytical Variability

    • Temperature

    • Humidity

    • Altitude (i.e. oxygen availability)

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Physiological limitations
Physiological limitations choices of sample type and technology

  • Sample choice

    • Capillary, venous, or arterial

      • Actual concentrations are different and relationship may vary

      • If capillary; hypotension, perfusion and other conditions such as Reynaud’s syndrome disturb normal relationship

      • Alternate site time lag

      • pO2 differences

  • Hematocrit

  • Smaller sample sizes increase the potential for residue to influence results

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Some relevant examples
Some relevant examples choices of sample type and technology

  • How a pO2 dependence became a maltose interference

  • Hematocrit effects

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The po 2 effect
The pO choices of sample type and technology2 effect

glucose + O2 + H2O

GO

(YSI and Beckman Glucose Analyzer)

gluconic acid + H2O2

HRPO

H2O2 + dye precursor dye color + H20

(colorimetric)

GO

glucose + med (ox) gluconolactone + med (red)

(electrochemical)

Epot

med (red) e- + med (ox)

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How a po2 interference became a maltose interference
How a pO2 interference became a maltose interference choices of sample type and technology

  • Original methods based on glucose oxidase coupled to a colorimetric indicator system.

    • Oxygen available from atmosphere

      • blood removed by blotting, wiping etc.

      • exposed to air during the reaction time

  • Electrochemical methods used mediators

    • Systems calibrated for capillary blood

  • Oxygen would interfere competitively

    • Use of venous or arterial blood exacerbated this competition

      • Venous reads higher; less 02 competition

      • Arterial reads lower; more 02 competition

    • pO2 effects generally greater at lower glucose concentrations

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How a po2 interference became a maltose interference1
How a pO2 interference became a maltose interference choices of sample type and technology

  • Second Generation products

    • GO

      • Open to atmospheric oxygen

      • Oxygen blocked by windows or capillary design

    • Hexokinase/G6PDH

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How a po2 interference became a maltose interference2
How a pO2 interference became a maltose interference choices of sample type and technology

  • GDH-PQQ systems introduced to alleviate pO2

    • GDH reaction does not involve oxygen

    • RT stable enzyme

  • However, GDH-PQQ less specific for glucose

    • Recognizes maltose, galactose, xylose and other sugars with glucose moiety, with false elevation of glucose results.

  • Recent versions of GDH with NAD or FAD cofactor are more specific and stable.

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Hematocrit effects
Hematocrit effects choices of sample type and technology

  • For a rapid test, WB is preferable if not necessary

  • Most systems now report “plasma equivalent”

  • Systems are calibrated at normal hematocrit.

  • WB sample hematocrits may vary significantly (~15 to >70)

  • Glucose content of whole blood as compared to plasma is inversely related with hematocrit.

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Hematocrit dependence
Hematocrit dependence choices of sample type and technology

Little method effect

Greater method effect

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Hematocrit effects1
Hematocrit effects choices of sample type and technology

  • Hematocrit may influence access of plasma or diffusion of glucose to measurement system suppressing results.

  • Hematocrit effects generally greater at higher glucose concentrations

  • Hematocrit can be measured and corrected for

    • Greater imprecision?

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In conclusion
In Conclusion choices of sample type and technology

  • Limitations and interferences are related to the particular technologies chosen.

  • The unique goals of a BGM system make it unlikely they will ever completely match a lab based system.

  • The evolution of BGM devices is a demonstration of achieving a balance between a high degree of performance with a rapid, more versatile, easy to use system.

  • Using a WB sample and reporting plasma (unless corrected for) introduces a ± 6% error in the range 25-65 hct.

Ken Ervin Consulting Services


Ken Ervin Consulting Services choices of sample type and technology


Ken Ervin Consulting Services choices of sample type and technology


Ken Ervin Consulting Services choices of sample type and technology


Ken Ervin Consulting Services choices of sample type and technology


Ken Ervin Consulting Services choices of sample type and technology


Ken Ervin Consulting Services choices of sample type and technology


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