Methods that are currently available for people diagnosed with diabetes to self-test and self-monitor monitor blood glucose levels can be categorized as conventional/traditional glucose monitoring technologies, continuous glucose monitoring technologies, or non-invasive glucose monitoring technologies.^{1, 2, 5–10}

Conventional/traditional glucose monitoring technologies are portable devices also known as blood glucometers or blood glucose meters (BGMs).^{1, 5–10} BGMs provide intermittent readings where user activity is necessary to perform the test and measure glucose levels as and when required several times a day. To perform glucose measurement, the user has to puncture capillary blood vessels using a lancing device and a lancet to obtain a small blood sample. The blood sample is transferred to a test strip inserted into the BGM, which then provides a result on the measured glucose level. The BGM is only one component of a conventional/traditional blood glucose monitoring system, which typically also includes disposable test strips, lancing devices, lancets, and quality control solutions. Other components and accessories may include USB ports and cables, software and smartphone applications, and log books. Some of these (e.g., lancing device) may be sold together with the BGM in a kit, and others may be sold separately (e.g., test strips).

For most of the available conventional/traditional blood glucose monitoring systems, glucose measurement is based on the amperometry principle (using electrochemical biosensor technology).^{2, 7, 11} Electrochemical biosensor technology uses electrodes to detect a small intensity electrical current generated during a chemical reaction when the glucose in the blood sample mixes with the special chemicals (glucose enzyme reagents) in the test strip. The intensity of the electrical current produced depends on and changes with the amount of glucose in the blood sample. The meter measures the strength of the electrical current, calculates the blood glucose level, and then displays the result. For some systems, glucose measurement is based on the photometry principle (using photometric technology). These systems include a handheld analyzer and disposable test strips that contain the glucose enzyme reagent. The analyzer measures the extent of colour change caused by the presence of glucose in the blood sample. The amount of colour change is related to the glucose concentration in the blood glucose sample.

BGMs are deemed as invasive and painful technologies because they require blood sampling to measure glucose.^{1, 2, 5–10} The main disadvantage of using this method is that it only provides the blood glucose concentration at the time of measurement and reading without giving information about the glucose trends. However, recent advances have enabled the development of continuous glucose monitoring systems.

Continuous glucose monitoring (CGM) systems consist of wearable technologies designed to measure and monitor blood glucose levels continuously and automatically, based on the interstitial fluid (the fluid between the cells below the skin surface).^{1, 5–10} They can provide information on blood glucose levels every five minutes and produce data that show trends in glucose measurements. A typical CGM system consists of a glucose sensor, a radio transmitter, and a reader/receiver. The sensor is contained in a small needle inserted just under the skin, which is kept securely in place by an adhesive patch and worn for a number of days until replacement. The sensor contains a chemical that reacts with the glucose in the interstitial fluid, triggering a small electric current. The transmitter (which is clipped to the sensor after it is inserted under the skin) receives the electric current from the sensor and wirelessly sends information about the glucose levels to the receiver, a handheld wearable device (the size of a pager or cellphone) that records and displays results. While the transmitter and the receiver are reusable and rechargeable components, the sensors are disposable components with a life expectancy depending on the system used (up to seven days for the CGM systems currently approved and available in North America¹²).

CGM systems are deemed to be minimally invasive technologies because they compromise the skin barrier but do not puncture any blood vessels.^{1, 5–10} However, they require routine replacement and calibration by the patient using measurements from approved and commercially available BGMs. According to US Food and Drug Administration (FDA) labelling, currently approved CGM systems require a prescription and are not intended as an alternative to traditional glucose self-monitoring, but rather to serve as a complement in supplying additional information on a user’s glucose trends that are not available solely from BGMs. Users of currently approved CGM systems are recommended to confirm glucose levels with an approved and commercially available BGM before making a change in treatment.^{1, 7, 8, 13} CGM systems are recommended only for people with type 1 diabetes who use intensive insulin therapy, and some can be linked with an insulin pump.^{7, 8}

The latest technological advances are focused on non-invasive glucose monitoring technologies.

Non-invasive glucose monitoring technologies (NIGMs) are designed to measure and monitor blood glucose levels by using various optical, transdermal and other methods, without drawing blood and without compromising the skin barrier.^{1, 2, 5, 6, 14, 15} They aim to provide intermittent readings similar to BGMs, where patient activity is necessary to perform the test or continuous readings similar to the currently used CGM systems. However, they work on different principles such as the absence of biological components.¹

Currently available BGMs, CGM systems, and NIGMs vary in terms of ease of use, accuracy of test results, size, weight, blood drop size (if blood sampling is required), testing time, availability of alternate site testing, the amount of data storage and memory capabilities, visibility, ability to mark or flag a reading, high-tech features, usability, cost (retail price), and reimbursement.^{1, 6, 12, 13, 16} Some glucose monitoring technologies can also measure blood ketones or blood pressure. Others can be linked to and communicate with insulin pumps. Many glucose monitoring technologies can now sync with a computer, smart phone, or other device. Most companies have converted their offline downloads to the “cloud,” allowing for data access by patients and clinicians. Diabetes data management platforms make data from devices of different manufacturers available to the patient and clinician through a universal portal or smartphone application.