Many diabetics may have some questions when using a blood glucose meter.

Why the test reading got from home blood glucose meter different from the test results got from hospital?
Most glucose meters are well designed and give reasonably accurate test results. It is not like lab equipment but it still has its own ISO standard (ISO 15197) to follow. Blood glucose meters are considered clinically accurate if the result is within 15mg/dL (<100 mg/dL) or 15% (100 mg/dL) of what a lab test would indicate.
For example, if your glucose meter result (whole blood) was 200 mg/dL, and the lab test result (plasma) was 230 mg/dL, the difference % will be (whole blood glucose value - plasma blood glucose value) / plasma*100, the result will be (200-230)/230*100=-13%, which has met the ISO 15197 standard.

Why were results different after measuring blood sugar twice in a row?
For example: I used the portable blood glucose meter to check the blood sugar before having my breakfast, the first result was 270 mg/dL, and I tested it again immediately; however, the second one was 230 mg/dL. Which one was correct?
In fact, both of the results were pretty high. You got 2 different results because of your blood circulation and the sugar mixed into the blood. You might test a blood drop with your meter that has more glucose; you might test next blood drop that contains less glucose. Both reflected in your 2 different blood glucose checks. Basically, there is an about 5% difference when using the same blood sample but both are accurate.

Why the results measured by different companies\' blood glucose meters are different?
The test results for the same blood sample may vary because each manufacturer\'s blood glucose meter setting is different,. Therefore, it is not recommended to compare different brands of blood glucose meters.