Blood glucose monitoring

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Blood glucose testing, showing the size of blood drop required by modern meters.

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Blood glucose monitoring is a way of testing how much glucose is in the blood (glycemia).

This is important in the care of diabetes mellitus. Most people with Type 2 diabetes need to test at least once per day (usually before breakfast) to assess the effectiveness of their diet and exercise for controlling their blood glucose levels.[citation needed] Many people with Type 2 are using an oral medication to combat their insulin resistance, and must test their blood glucose before and after breakfast to assess the effectiveness of their dosage. All people who need to inject insulin, both for Type 1 diabetes and Type 2, need also to test their blood sugar more often (3 to 10 times per day) to assess the effectiveness of their prior insulin dose and to calculate their next insulin dose.

Improved technology for measuring blood glucose is rapidly changing the standards of care for all diabetic people. There are several methods of blood glucose testing currently available.

Chemical Test Strips

Chemical test strips are a low cost method for monitoring blood glucose. A fairly large drop of blood, usually taken from the fingertip, is placed on a chemically prepared strip, called a blood glucose testing strip. The strip chemistry will cause it to change color according to the amount of glucose is in the blood. One can tell if their level of blood glucose is low, high, or normal by comparing the color on the end of the strip to a color chart that is printed on the side of the test strip container.

These are recommended only for people who are occasionally monitoring their blood glucose level (prediabetic or type 2) and are not using insulin.

The Betachek Diabetes Test Strips

Pamphlet for Use of Chemical Test Strips

Blood Glucose Meters

Four generations of blood glucose meter, c. 1993-2005. Sample sizes vary from 30 to 0.3 μl. Test times vary from 5 seconds to 2 minutes (modern meters are typically below 15 seconds).

A blood glucose meter is an electronic device for measuring the blood glucose level. A relatively small drop of blood is placed on a disposable test strip which interfaces with a digital meter. Within several seconds, the level of blood glucose will be shown on the digital display.

While more expensive, blood glucose meters seem a breakthrough in diabetes self care. As the drops of blood needed for the meter become smaller, the pain associated with testing is reduced and the compliance of diabetic people to their testing regimens is improved. Although the cost of using blood glucose meters seems high, it is believed to be a cost benefit relative to the avoided medical costs of the complications of diabetes.

A recent and welcome advance is the use of small blood drops for blood glucose testing from other places than the finger tips. This alternate site testing uses the same test strips and meter, is practically pain free, and gives the real estate on the finger tips a needed break if they become sore.

Self-monitored blood glucose (SMBG)

Evidence of efficacy and impact

It is not clear that home monitoring is helpful in non-insulin treated diabetes mellitus type 2.

  • One randomized controlled trial found that self-monitoring of blood glucose did not improve the Hba1c among "reasonably well controlled non-insulin treated patients with type 2 diabetes".[1][2]
  • A more recent meta-analysis in 2012 did not find benefit[3].

A more recent randomized controlled trial in 2019 found:

  • A significant reduction in HbA1c of 0.8% among patients whose baseline HbA1c was > 7.5%[4]

Continuous Blood Glucose Monitoring (CBGM)

CBGM is different than closed-loop systems (artificial pancreas)[5].

A continuous blood glucose monitor determines blood glucose levels on a continuous basis (every few minutes). A typical system consists of:

  • a disposable glucose sensor placed just under the skin, which is worn for a few days until replacement,
  • a link from the sensor to a non-implanted transmitter which communicates to a radio receiver,
  • an electronic receiver worn like a pager (or insulin pump) that displays blood glucose levels on a practically continuous manner, as well as monitors rising and falling trends in glycemic excursions.

Continuous blood glucose monitors measure the glucose level of interstitial fluid. Disadvantages compared to traditional blood glucose monitoring are:

  1. continuous systems must be calibrated with a traditional blood glucose measurement (using current technology) and therefore do not yet fully replace "fingerstick" measurements.
  2. glucose levels in interstitial fluid lag temporally behind blood glucose values.

Patients therefore require traditional fingerstick measurements for calibration (typically twice per day) and are often advised to use fingerstick measurements to confirm hypo- or hyperglycemia before taking corrective action.

The lag time discussed above has been reported to be about 5 minutes.[6][7][8] Anecdotally, some users of the various systems report lag times of up to 10-15 minutes. This lag time is insignificant when blood sugar levels are relatively consistent. However, blood sugar levels, when changing rapidly, may read in the normal range on a CGM system while in reality the patient is already experiencing symptoms of an out-of-range blood glucose value and may require treatment. Patients using CGM are therefore advised to consider both the absolute value of the blood glucose level given by the system as well as any trend in the blood glucose levels. For example, a patient using CGM with a blood glucose of 100 mg/dl on their CGM system might take no action if their blood glucose has been consistent for several readings, while a patient with the same blood glucose level but whose blood glucose has been dropping steeply in a short period of time might be advised to perform a fingerstick test to check for hypoglycemia.

Continuous monitoring allows examination of how the blood glucose level reacts to insulin, exercise, food, and other factors. The additional data can be useful for setting correct insulin dosing ratios for food intake and correction of hyperglycemia. Monitoring during periods when blood glucose levels are not typically checked (e.g. overnight) can help to identify problems in insulin dosing (such as basal levels for insulin pump users or long-acting insulin levels for patients taking injections). Monitors may also be equipped with alarms to alert patients of hyperglycemia or hypoglycemia so that a patient can take corrective action(s) (after fingerstick testing, if necessary) even in cases where they do not feel symptoms of either condition. While the technology has its limitations, studies have demonstrated that patients with continuous sensors experience less hyperglycemia and also reduce their glycated hemoglobin levels.[9][10][11][12]

See this summary by a diabetes support group for a review of CBGM products, performance, and features.

This technology is an important component in the effort to develop a closed-loop system connecting real-time automatic control of an insulin pump based on immediate blood glucose data from the sensor. One important goal is to develop an algorithm for automatic control, by which the system would function as an artificial pancreas. However, this is a long-term goal at this point for companies that manufacture such systems, as such an algorithm would need to be very complex in order to accurately control blood sugar levels without any user input.

Evidence of efficacy and impact

Continuous glucose monitoring, according to a meta-analysis or randomized controlled trials, "modest reduction in HbA1c (WMD -0.17%, 95% CI -0.29 to -0.06, I2 = 96.2%),"[13]

Randomized controlled trials of continuous glucose monitoring in Diabetes mellitus type 1[14][15][16][17][17][18][19] and Diabetes mellitus type 2[20]
Children Adults
Diabetes mellitus type 1 CITY, 2020[14] GOLD, 2017[16]
DIAMOND, 2017[17]
HypoDE, 2018[18]
WISDM, 2020[15]


Diabetes mellitus type 2[20] MOBILE

For patients with diabetes mellitus type 1

  • Flash and real-time monitoring have been compared[21]

For patients with diabetes mellitus type 2

  • "Evidence suggests that RT-CGM and P-CGM are effective in improving HbA1c in adults with type 2 diabetes" according to a meta-analysis. [22]
  • THe more recent MOBILE randomized controlled trial reported better diabetes control in spite of no difference in insuling dosing[20]. An accompanying editorial questioned whether this was due to increased patient engagement[20].

Insurance coverage

Currently, continuous blood glucose monitoring is not automatically covered by health insurance in the United States in the same way that most other diabetic supplies are covered (e.g. standard glucose testing supplies, insulin, and even insulin pumps). However, an increasing number of insurance companies do cover continuous glucose monitoring supplies (both the receiver and disposable sensors) on a case-by-case basis if the patient and doctor show a specific need. The lack of insurance coverage is exacerbated by the fact that disposable sensors must be frequently replaced (sensors by Dexcom and Minimed have been FDA approved for 7- and 3-day use, respectively, though some patients wear sensors for longer than the recommended period) and the receiving meters likewise have finite lifetimes (less than 2 years and as little as 6 months). This is one factor in the slow uptake in the use of sensors that have been marketed in the United States.


Some current and future continuous glucose monitoring products include:

The Miao Miao is a smartreader add on for the d-Nav that sends readings to a smartphone.

Glucose sensing bio-implants

Longer term solutions to continuous monitoring, not yet available but under development, use a long-lasting bio-implant. These systems promise to ease the burden of blood glucose monitoring for their users, but at the trade off of a minor surgical implantation of the sensor that lasts from one year to more than five years depending on the product selected.

Products under development include:

Non-Invasive Technologies

Some new technologies to monitor blood glucose levels will not require access to blood to read the glucose level. Non-invasive technologies include near IR detection, ultrasound and dielectric spectroscopy. These will free the person with diabetes from finger sticks to supply the drop of blood for blood glucose analysis.

Most of the non-invasive methods under development are continuous glucose monitoring methods and offer the advantage of providing additional information to the subject between the conventional finger stick, blood glucose measurements and over time periods where no finger stick measurements are available (i.e. while the subject is sleeping).

Products under development include:


  1. Farmer A, Wade A, Goyder E; et al. (2007). "Impact of self monitoring of blood glucose in the management of patients with non-insulin treated diabetes: open parallel group randomised trial". doi:10.1136/bmj.39247.447431.BE. PMID 17591623.
  2. Farmer AJ, Perera R, Ward A, Heneghan C, Oke J, Barnett AH; et al. (2012). "Meta-analysis of individual patient data in randomised trials of self monitoring of blood glucose in people with non-insulin treated type 2 diabetes". BMJ. 344: e486. doi:10.1136/bmj.e486. PMID 22371867. Review in: Ann Intern Med. 2012 Jun 19;156(12):JC6-12
  3. Willett LR (2012). "ACP Journal Club. Meta-analysis: self-monitoring in non-insulin-treated type 2 diabetes improved HbA1c by 0.25%". Ann Intern Med. 156 (12): JC6–12. doi:10.7326/0003-4819-156-12-201206190-02012. PMID 22711113.
  4. Parsons SN, Luzio SD, Harvey JN, Bain SC, Cheung WY, Watkins A; et al. (2019). "Effect of structured self-monitoring of blood glucose, with and without additional TeleCare support, on overall glycaemic control in non-insulin treated Type 2 diabetes: the SMBG Study, a 12-month randomized controlled trial". Diabet Med. 36 (5): 578–590. doi:10.1111/dme.13899. PMC 6593419 Check |pmc= value (help). PMID 30653704.
  5. Breton MD, Kanapka LG, Beck RW, Ekhlaspour L, Forlenza GP, Cengiz E; et al. (2020). "A Randomized Trial of Closed-Loop Control in Children with Type 1 Diabetes". N Engl J Med. 383 (9): 836–845. doi:10.1056/NEJMoa2004736. PMID 32846062 Check |pmid= value (help).
  6. Iris M. Wentholt, Marit A. Vollebregt, Augustus A. Hart, Joost B. Hoekstra, and J. Hans DeVries. Comparison of a Needle-Type and a Microdialysis Continuous Glucose Monitor in Type 1 Diabetic Patients. Diabetes Care, 2005 28: 2871-2876
  7. Steil, G.M., Rebrin, K. Mastrototaro,J., Bernaba, B., and Saad, M.F. Determination of Plasma Glucose During Rapid Glucose Excursions with a Subcutaneous Glucose Sensor. Diabet. Technol. Ther. 2003, 5: 27-31
  8. Wilhelm, B., Forst, S., Weber, M.M., Larbig, M., Pfûtzner, A., and Forst, T. Evaluation of CGMS® During Rapid Blood Glucose Changes in Patients with Type 1 Diabetes. Diabet. Technol. Ther. , 2006, 8: 146-155
  9. Garg, S., Zisser H., Schwartz, S., Baile, T., Kaplan, R., Ellis, S., and Jovanovic, L. Improvement in Glycemic Excursions With a Transcutaneous, Real-Time Continuous Glucose Sensor. Diabetes Care, 2006. 29:44-50
  10. Deiss, D., Bolinder, J., Riveline, J-P., Battelino, T., Bose, E., Tubiana-Rufi, N., Kerr, D., and Phillip, M. Improved glycemic control in poorly controlled patients with type 1 diabetes using real-time continuous glucose monitoring. Diabetes Care, 2006. 29 (12): 2730-2732
  11. Mastrototaro, J.J., Cooper, K.W., Soundararajan, G., Sanders, J.B., and Shah, R.B. Adv Ther. 2006 Sep-Oct;23(5):725-32
  12. Relationship of fasting and hourly blood glucose levels to HbA1c values: safety, accuracy, and improvements in glucose profiles obtained using a 7-day continuous glucose sensor. Garg, S. and Jovanovic, L. Diabetes Care 2006 Dec;29(12):2644-9
  13. Maiorino MI, Signoriello S, Maio A, Chiodini P, Bellastella G, Scappaticcio L; et al. (2020). "Effects of Continuous Glucose Monitoring on Metrics of Glycemic Control in Diabetes: A Systematic Review With Meta-analysis of Randomized Controlled Trials". Diabetes Care. 43 (5): 1146–1156. doi:10.2337/dc19-1459. PMID 32312858 Check |pmid= value (help).
  14. 14.0 14.1 Laffel LM, Kanapka LG, Beck RW, Bergamo K, Clements MA, Criego A; et al. (2020). "Effect of Continuous Glucose Monitoring on Glycemic Control in Adolescents and Young Adults With Type 1 Diabetes: A Randomized Clinical Trial". JAMA. 323 (23): 2388–2396. doi:10.1001/jama.2020.6940. PMC 7298603 Check |pmc= value (help). PMID 32543683 Check |pmid= value (help).
  15. 15.0 15.1 Pratley RE, Kanapka LG, Rickels MR, Ahmann A, Aleppo G, Beck R; et al. (2020). "Effect of Continuous Glucose Monitoring on Hypoglycemia in Older Adults With Type 1 Diabetes: A Randomized Clinical Trial". JAMA. 323 (23): 2397–2406. doi:10.1001/jama.2020.6928. PMC 7298607 Check |pmc= value (help). PMID 32543682 Check |pmid= value (help).
  16. 16.0 16.1 Lind M, Polonsky W, Hirsch IB, Heise T, Bolinder J, Dahlqvist S; et al. (2017). "Continuous Glucose Monitoring vs Conventional Therapy for Glycemic Control in Adults With Type 1 Diabetes Treated With Multiple Daily Insulin Injections: The GOLD Randomized Clinical Trial". JAMA. 317 (4): 379–387. doi:10.1001/jama.2016.19976. PMID 28118454.
  17. 17.0 17.1 17.2 Beck RW, Riddlesworth T, Ruedy K, Ahmann A, Bergenstal R, Haller S; et al. (2017). "Effect of Continuous Glucose Monitoring on Glycemic Control in Adults With Type 1 Diabetes Using Insulin Injections: The DIAMOND Randomized Clinical Trial". JAMA. 317 (4): 371–378. doi:10.1001/jama.2016.19975. PMID 28118453.
  18. 18.0 18.1 Heinemann L, Freckmann G, Ehrmann D, Faber-Heinemann G, Guerra S, Waldenmaier D; et al. (2018). "Real-time continuous glucose monitoring in adults with type 1 diabetes and impaired hypoglycaemia awareness or severe hypoglycaemia treated with multiple daily insulin injections (HypoDE): a multicentre, randomised controlled trial". Lancet. 391 (10128): 1367–1377. doi:10.1016/S0140-6736(18)30297-6. PMID 29459019. Review in: Ann Intern Med. 2018 May 15;168(10):JC53
  19. 19.0 19.1 Visser, Margaretha M; Charleer, Sara; Fieuws, Steffen; De Block, Christophe; Hilbrands, Robert; Van Huffel, Liesbeth; Maes, Toon; Vanhaverbeke, Gerd; Dirinck, Eveline; Myngheer, Nele; Vercammen, Chris; Nobels, Frank; Keymeulen, Bart; Mathieu, Chantal; Gillard, Pieter (2021). "Comparing real-time and intermittently scanned continuous glucose monitoring in adults with type 1 diabetes (ALERTT1): a 6-month, prospective, multicentre, randomised controlled trial". The Lancet. 397 (10291): 2275–2283. doi:10.1016/S0140-6736(21)00789-3. ISSN 0140-6736.
  20. 20.0 20.1 20.2 20.3 Peek ME, Thomas CC (2021). "Broadening Access to Continuous Glucose Monitoring for Patients With Type 2 Diabetes". JAMA. 325 (22): 2255–2257. doi:10.1001/jama.2021.6208. PMID 34077505 Check |pmid= value (help).
  21. Reddy M, Jugnee N, Anantharaja S, Oliver N (2018). "Switching from Flash Glucose Monitoring to Continuous Glucose Monitoring on Hypoglycemia in Adults with Type 1 Diabetes at High Hypoglycemia Risk: The Extension Phase of the I HART CGM Study". Diabetes Technol Ther. 20 (11): 751–757. doi:10.1089/dia.2018.0252. PMC 6208158. PMID 30265562.
  22. Park C, Le QA (2018). "The Effectiveness of Continuous Glucose Monitoring in Patients with Type 2 Diabetes: A Systematic Review of Literature and Meta-analysis". Diabetes Technol Ther. 20 (9): 613–621. doi:10.1089/dia.2018.0177. PMID 30095980.