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Factors affecting blood glucose monitoring

All GlucoRx Nexus meters comply with the requirements of ISO 15197:2015. This standard states that 95% of the meter readings above 4.2mmol/l would have to be +/- 15% compared with the reference method ‘YSI-2300 glucose analyser’. The YSI is the laboratory meter that all meters are calibrated to; it is incorrect to compare one blood glucose meter to another.

The accuracy of your Nexus blood glucose monitoring system, although uses enhanced GDH-FAD enzyme test strip technology, can be affected by the following factors:

  • Incorrect meter calibration , as per the operating manual instructions. Tightly close and store your control solution between 2 °C and 30 °C. The control solution, meter, and test strips should come to room temperature (20°C-25°C) before testing. Shake the vial thoroughly, gently squeeze out then wipe off the first drop of control solution, and wipe the dispenser tip to ensure a good clean sample as well as accurate result. Hold your meter to move the absorbent hole of test strip to touch the drop. Once the confirmation window fills completely, the meter will begin counting down. To avoid contaminating the control solution, do not directly apply solution onto a strip. Use the solution for 3 months only after first opening, then discard.
  • Patient technique can greatly influence the accuracy of your blood glucose meter. Hold the meter to move the absorbent hole of test strip to touch a generous drop of blood to completely fill the strip confirmation window; do not add more blood to the test strip after the first drop is applied.
  • Size and quality of your blood sample and pressure used to wipe blood off the test strip . Always discard your first drop of blood – because of cell debris and tissue fluid at the puncture site – and gently squeeze out and test the second drop.
  • Hand washing your testing site with soap and water and proper drying is very important with new smaller-volume meters now. The tiniest amount of dirt, alcohol or other skin contaminant can significantly raise blood glucose. For example with a 0.3μl blood sample, 1μg of glucose (weight of a dust particle) will increase results by 16.7μl. * In the UK the use of alcohol wipes when testing blood glucose is no longer recommended.
  • Oxygen levels of your blood.
  • Most diabetics will have normal haematocrit (red blood cell count), but certain groups (i.e. patients who live at different altitudes, smokers, those with renal failure) may have significant haematocrit alterations which can cause serious errors in blood glucose measurement. Haematocrit levels can vary from person to person, throughout the day and also be affected by medicines and supplements.
  • High levels of certain medicines or substances, such as ascorbic acid, in your blood.
  • Slight strip-to-strip variation in manufacturing; no two test strips are the same and batches can vary.
  • Storing the test strips at high temperature or high humidity, or in an open vial (allowing the humidity to get to the strips) can shorten their life and affect results. Keep your glucose meter and test strips at room temperature (20°C-25°C). Low temperature diminishes circulation to the skin. This does not influence a glucose reading taken from a fingertip, but blood flow to your forearm skin is dramatically lowered. Alternative site testing , which normally has a lag of 15–30 minutes, can have a lag of up to an hour when the arm is cooled. Blood sugar results can be less accurate if you test at places other than the fingertips (e.g., arm, hand, leg). This should not be a problem if you always use one site. However, when the blood sugar is rising rapidly (e.g., immediately after eating) or falling rapidly (in response to insulin or exercise), testing at alternate sites may give significantly different results than a fingerstick reading. In these situations, fingertip testing is preferred.
  • Monitor problems – Fully insert the test strip into your monitor. Replace the monitor batteries as needed.
  • Test strip problems – Dispose of damaged or outdated test strips; lack of enzyme coverage in these can cause inaccuracies. Store your strips in their sealed container, away from heat, moisture and humidity. Be sure the strips are meant for your specific glucose meter.
  • Blood glucose meters are least accurate during episodes of low blood sugar, and if you are severely dehydrated from excessive vomiting, diarrhoea, or urination.

Download further information on Factors affecting blood glucose monitoring: Sources of Errors in Measurement

Download Review Article on Interferences and Limitations in Blood Glucose Self-Testing