The old chestnut rears it's head again, it's only been, what 2 weeks.
Do not compare meters. Stick to one make.
Meters are supposed to stick to an ISO standard:
ISO 15197 created in 2003 is: 95 % of the
individual glucose results shall fall within ? 0.83 mmol/
L of the results of the manufacturer?s measurement procedure at glucose concentrations< 4.2 mmol/L and within ? 20 % at glucose concentrations
>=4.2 mmol/L
So any reading above 4.2 has an accuracy of +/-20%. So a reading of 20 could really be 17 or 24.
The biggest contributor to inaccuracy is the strips. Here?s the process is: glucose interacts with an enzyme on the strip, releasing electrons. Another agent on the strip, called the ?mediator,? turns these electrons into an electrical current. The greater the glucose concentration, the greater the current. That current then speeds through the strip. Finally, an algorithm (formula) in the meter converts the current into a concentration of glucose. And voila! You get a number.
But there?s a long list of factors that affect meter/strip accuracy:
Meter calibration, coding, enzymes and mathematical algorithms (all different in different meters)
Variable enzymes in strips
Mediator oxidation and strip freshness/age
Strips differ somewhat, lot to lot, with somewhat different precision ranges for each lot
Strips differ in well size (the space in a strip that holds the blood)
Interfering substances in one?s blood from medications, and every manufacturer?s nightmare, hematocrit ? that percentage of red blood cells in blood, which can interfere with the electrical current
Environmental conditions: temperature, climate, altitude
Lack of meter maintenance
User error ? forgetting to code the meter or coding it incorrectly; not washing hands before testing (there may be some sugar residue on your fingers or sweat on hands); leaving strips exposed to air too long; or using expired strips
As for testing twice on the same meter a minute apart and getting a different number, the first drop of blood you squeeze out of your finger is not the same as the next drop of blood. It may contain more interstitial fluid (the solution that surrounds our cells), which can give a lower reading.
Meters, especially the big names, tend to do better on accuracy than the ISO standard. Some even claim 10% accuracy. Hospital lab equipment isn't 100% accurate either, supposedly around the 4% accuracy.
