The most widely known method of checking blood sugar is using the finger-prick method with a glucometer. Once pricked , you can place the drop of blood on strip. The strip is then inserted into a meter that measures the amount of glucose attached to your blood cells.
You can check your blood sugar level without the need for finger sticks or needles by using a Continuous Glucose Monitor (CGM) or flash monitor.
While glucometer gives you the capillary blood glucose, CGM reflects the interstitial glucose levels. The standard one is always measuring the venous blood glucose as done in blood tests(withdrawal by venipuncture). CGM (Interstitial glucose) lags behind the blood glucose by 30 min.
While there is nothing much of a difference between Standard venous sampling and Glucometer (capillary) levels in measuring Fasting glucose since the body runs on fats during fasting , there is a difference of up to 20-25 % between these two in the postprandial period since the body runs on glucose after eating with high numbers in the glucometer.