Analytical Interferences and Physiological Limitations of Blood Glucose Meters Ken Ervin

Ken Ervin Consulting Services Published information 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 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

Ken Ervin Consulting Services Package inserts address “Procedural limitations” Sample related  e.g. Hct, pO 2, DKA, HHNK, etc. Endogenous compounds Exogenous compounds Environmental  Temperature  Humidity  Altitude

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

Ken Ervin Consulting Services BGM Design Goals Drive the specifications and choice of technology Accurate and precise 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

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

Ken Ervin Consulting Services BGM measurement based on combining technologies 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

Ken Ervin Consulting Services Interferences and physiological limitations are related to choices of sample type and technology

Ken Ervin Consulting Services Interferences result from Analyte specificity issues or Sample and environmental influences on the measurement reaction

Ken Ervin Consulting Services Analyte specificity Use of enzymes specific for glucose  GO  GDH  Hexokinase/G6PDH

Ken Ervin Consulting Services Sample influences on measurement Endogenous substances  Uric acid  Bilirubin  Lipemia, Hemolysis Exogenous substances  Acetominophen  Ascorbate  Maltose, Icodextrin metabolites  Mannitol  Dopamine

Ken Ervin Consulting Services Sample influences DKA, HHNK  pH and/or Viscosity Hyperosmolar, flow effects Less water volume to reconstitute reagent

Ken Ervin Consulting Services Environmental influences Analytical Variability  Temperature  Humidity  Altitude (i.e. oxygen availability)

Ken Ervin Consulting Services Physiological limitations 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 pO 2 differences Hematocrit Smaller sample sizes increase the potential for residue to influence results

Ken Ervin Consulting Services Some relevant examples How a pO 2 dependence became a maltose interference Hematocrit effects

Ken Ervin Consulting Services The pO 2 effect glucose + O 2 + H 2 O gluconic acid + H 2 O 2 GO glucose + med (ox) gluconolactone + med (red) GO H 2 O 2 + dye precursor dye color + H 2 0 HRPO (colorimetric) (electrochemical) med (red) e - + med (ox) E pot (YSI and Beckman Glucose Analyzer)

Ken Ervin Consulting Services How a pO2 interference became a maltose interference 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 0 2 competition Arterial reads lower; more 0 2 competition  pO2 effects generally greater at lower glucose concentrations

Ken Ervin Consulting Services How a pO2 interference became a maltose interference Second Generation products  GO Open to atmospheric oxygen Oxygen blocked by windows or capillary design  Hexokinase/G6PDH

Ken Ervin Consulting Services How a pO2 interference became a maltose interference GDH-PQQ systems introduced to alleviate pO 2  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.

Ken Ervin Consulting Services Hematocrit effects 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.

Ken Ervin Consulting Services Hematocrit dependence Little method effect Greater method effect

Ken Ervin Consulting Services Hematocrit effects 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?

Ken Ervin Consulting Services In Conclusion 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 hct.

Ken Ervin Consulting Services

Ken Ervin Consulting Services

Ken Ervin Consulting Services

Ken Ervin Consulting Services

Ken Ervin Consulting Services

Ken Ervin Consulting Services