How to get an accurate glucose reading for diabetic patients

Everything from outdated strips to poor timing can lead to wrong glucose measurements, but here’s how to reduce errors


Updated October 31, 2016

Diabetes is a significant health care problem in the United States and is the seventh leading cause of death [1]. EMS personnel frequently encounter patients experiencing some type of diabetic event. Familiarity with the pathophysiology, signs, and symptoms can help responders differentiate diabetic patients from other patients with similar symptoms.

Reasons for inaccurate glucose readings
One very common assessment step in a patient suspected of having a diabetic emergency is to determine the patient's blood glucose level, often by using a handheld monitor. It is important to note that handheld monitors can be divided into two distinct categories [2].  

Paramedics attend a diabetic man who lost control of his vehicle due to hypoglycemia. (Photo by Sbharris - Wikipedia commons own work, CC BY-SA 3.0)
Paramedics attend a diabetic man who lost control of his vehicle due to hypoglycemia. (Photo by Sbharris - Wikipedia commons own work, CC BY-SA 3.0)

Over-the counter monitors are designed for single patient use. These monitors allow a patient suffering from diabetes to monitor their own glucose state and adjust their self-administered medication based on those results. Point-of-care monitors are used in a professional setting such as an emergency department or EMS agency. POC monitors are designed for use on many patients.

Although a number of studies demonstrate acceptable accuracy for handheld blood glucose monitors under controlled conditions, accuracy is often suboptimal during actual clinical situations, which could have a significant impact on therapy [3, 4, 5, 6,7,8,9,10, 11, 12, 13, 14].

An Australian study demonstrates that meters tend to overestimate glucose levels when compared to reference values, with one common meter averaging about 25 mg/dl higher than the reference device.[4]In an investigation involving more than 18,000 patients, Canadian researchers found glucose measurement differences greater than 90 mg/dl in one in 200 meters designed for home use [15].

This degree of measurement error could result in patient self-administration of higher than necessary insulin doses, which could lead to hypoglycemic episodes. In fact, older meters may result in over administration of insulin by about 40 percent of patients using them [6]. If all patients suffering from Type 1 diabetes used the least accurate meter, the error would result in about 300,000 episodes of hypoglycemia per year [7].

For critically ill patients, POC glucose testing may overestimate glucose levels, especially in patients receiving blood pressure support through the use of vasopressors, in patients with diabetic ketoacidosis or hyperglycemic hyperosmolar syndrome [16, 17]

Capillary samples taken from patients with severe edema may underestimate by as much as 46 percent of reference value [12]. In these cases, the sample may be more representative of tissue glucose levels rather than capillary levels.

A number of factors may contribute to the measurement error associated with these devices. Poor or missing calibration, temperatures outside the intended range, outdated strips, improper technique, poor timing, insufficient sample size, and contamination can all provide misleading results. Repeated opening of the container used to store the test strips allows various contaminants a pathway of entry into the container.  In addition, touching more than one test strip to the inside of the container can also be the source of contamination. Contamination is especially serious, since it can happen so easily and is likely to result in episodes of hypoglycemia going unrecognized and untreated. Even a very tiny amount of glucose contamination can seriously alter a reading.

Minimizing errors 
By taking a few precautions, EMS personnel may increase the accuracy of the glucose values. The United States Food and Drug Administration (2009) recommends always using test strips recommended by the glucometer manufacturer. Use of an alternative brand of test strips can result in inaccurate results. In side-by-side comparisons against a known sample, researchers have demonstrated that different test strips will give noticeable variations in blood glucose values even when used in the same device [18].

Next, glucometers and test strips may be calibrated for either capillary or venous samples. Using venous blood to determine point-of-care glucose levels from tests strips calibrated for capillary blood can affect the accuracy of the reading. For the most accurate reading possible, obtain the blood sample from the source recommended by the glucometer and test strip manufacturer.

After swabbing the sample finger with alcohol, you must wipe the area dry with a sterile gauze pad. This allows any residual alcohol to be removed and avoids contamination of the sample blood.

For added accuracy, the first drop of blood available from the finger-stick should also be wiped with the gauze pad. This ensures that the second blood drop is the most accurate and least contaminated sample that can be taken.

Treatment basics
Caring for patients experiencing hypoglycemia requires greater urgency than for patients with hyperglycemia because the body, and especially the brain, depends heavily on glucose. The management goal for hypoglycemia is obvious. You must raise blood glucose levels of glucose before permanent brain damage can occur.

If the patient is still conscious and can provide airway self-protection, start with oral glucose. Place the gel under the tongue or in the pouch of the cheek. Encourage the patient to hold the gel in the mouth for as long as possible in order to maximize absorption. Take care to prevent the patient from aspirating the glucose and always have suction available.

If the patient is unconscious, treat the hypoglycemia with intravenous dextrose. Fifty-percent dextrose (D50) is virtually free of adverse effects but it is not without its hazards. D50 is a very concentrated form of sugar and if it infiltrates into the tissues from the IV site, extensive tissue necrosis is possible with widespread damage. The IV line must be patent in a large, stable vein before administration of dextrose in any concentration.

Effects of glucagon administration 
If the patient has an altered mental status or is unconscious and IV access is not possible, administer the hormone glucagon by either the intranasal or intramuscular route. Glucagon stimulates the liver to break down glycogen into glucose, which the body can use for energy production.

Glucagon administration will temporarily raise the blood glucose levels of the body; however, the drug takes 10 to 20 minutes to take effect. A two milligram intranasal dose is as effective within the first thirty minutes as a one milligram intramuscular dose [19].

Glucagon is only effective in patients with a sufficient reserve of glycogen in the liver. If the glycogen reserves have been depleted, such as might be the case in chronic alcoholics or patients with liver disease, the effectiveness of glucagon will be compromised.

The United States Food and Drug Administration has recently recommended implementation of two separate sets of standards for glucose meters, one for over-the-counter meters and one form POC meters.[20] These new standards will likely have a greater impact on the POC meters and improve the accuracy of glucose measurement in the prehospital environment.

References

1. Centers for Disease Control and Prevention. (2013). National diabetes fact sheet, 2011. Retrieved from http://www.cdc.gov/diabetes/pubs/pdf/ndfs_2011.pdf

2. Lias, C. (2014). Setting the bar for blood glucose meter performance. Retrieved from http://blogs.fda.gov/fdavoice/index.php/2014/01/setting-the-bar-for-blood-glucose-meter-performance/

3. Arabadjief, D., & Nichols, J. H. (2006). Assessing glucose meter accuracy. Current Medical Research and Opinion, 22(11), 2167-2174. doi:10.1185/030079906X148274

4. Cohen, M., Boyle, E., Delaney, C., & Shaw, J. (2006). A comparison of blood glucose meters in Australia. Diabetes Research and Clinical Practice, 71(2), 113-118. doi:10.1016/j.diabres.2005.05.013

5. Kuo, C. Y., Hsu, C. T., Ho, C. S., Su, T. E., Wu, M. H., & Wang, C. J. (2011). Accuracy and precision evaluation of seven self-monitoring blood glucose systems. Diabetes Technology and Therapeutics, 13(5), 596-600. doi:10.1089/dia.2010.0223

6. Boyd, J. C., & Bruns, D. E. (2001). Quality specifications for glucose meters: Assessment by simulation modeling of errors in insulin dose. Clinical Chemistry, 47(2), 209-214

7. Budiman, E. S., Samant, N., & Resch, A. (2013). Clinical implications and economic impact of accuracy differences among commercially available blood glucose monitoring systems. Journal of Diabetes, Science, and Technology, 7(2), 365-380. doi:10.1177/193229681300700213

8. Francescato, M. P., Geat, M., Stel, G., & Cauci, S. (2012). Accuracy of a portable glucose meter and of a continuous glucose monitoring device used at home by patients with type 1 diabetes. Clinica Chimica Acta, 413(1-2), 312-318. doi:10.1016/j.cca.2011.10.012

9. Hellman, R. (2012). Glucose meter inaccuracy and the impact on the care of patients. Diabetes/ Metabolism Research and Reviews, 28(3), 207-209. doi:10.1002/dmrr.2271

10. Henry, M. J., Major, C. A., & Reinsch, S. (2001). Accuracy of self-monitoring of blood glucose: Impact on diabetes management decisions during pregnancy. The Diabetes Educator, 27(4), 521-529. doi:10.1177/014572170102700407

11. Kanji, S., Buffie, J., Hutton, B., Bunting, P. S., Singh, A., McDonald, K., Fergusson, D., McIntyre, L. A., & Hebert, P. C. (2005). Reliability of point-of-care testing for glucose measurement in critically ill adults. Critical Care Medicine, 33(12), 2778-2785. doi:10.1097/01.CCM.0000189939.10881.60

12. Petersen, J. R., Graves, D. F., Tacker, D. H., Okorodudu, A. O., Mohammad, A. A., Cardenas, V. J. Jr. (2008). Comparison of POCT and central laboratory blood glucose results using arterial, capillary, and venous samples from MICU patients on a tight glycemic protocol. Clinica Chimica Acta, 396(1-2), 10-13. doi: 10.1016/j.cca.2008.06.01

13. Trajanoski, Z., Brunner, G. A., Gfrerer, R. J., Wach, P., & Pieber, T. R. (1996). Accuracy of home blood glucose meters during hypoglycemia. Diabetes Care, 19(12), 1412-1415.

14. Virdi, N. S., Mahoney, J. J. (2012). Importance of blood glucose meter and carbohydrate estimation accuracy. Journal of Diabetes Science and Technology, 6(4), 921-926.

15. Naugler, C., Zhang, Z., & Redman, L. (2014). Performance of community blood glucose meters in Calgary, Alberta: An analysis of quality assurance data. Canadian Journal of Diabetes, 38(5), 326-328. doi:10.1016/j.jcjd.2014.04.004

16. Critchell, C. D., Savarese, V., Callahan, A., Aboud, C., Jabbour, S., & Marik, P. (2007). Accuracy of bedside capillary blood glucose measurements in critically ill patients. Intensive Care Medicine, 33(12), 2079–2084. doi:10.1007/s00134-007-0835-4

17. Corl, D. E., Yin, T. S., Mills, M. E., Spencer, T. L., Greenfield, L., Beauchemin, E., Cochran, J., Suhr, L. D., Thompson, R. E., & Wisse, B. E. (2013). Evaluation of point-of-care blood glucose measurements in patients with diabetic ketoacidosis or hyperglycemic hyperosmolar syndrome admitted to a critical care unit. Journal of Diabetes, Science, and Technology, 7(5), 1265-1274.

18. Lenhard, M. J., DeCherney, G. S., Maser, R. E., Patten, B. C., & Kubik, J. (1995). A comparison between alternative and trade name glucose test strips. Diabetes Care, 18(5), 686-689. doi:10.2337/diacare.18.5.686

19. Pontiroli, A., Calerara, A., Pajetta, E., Albertetto, M., & Pozza, G. (1989). Intranasal glucagon as a remedy for hypoglycemia. Studies in healthy subjects and type 1 diabetic patients. Diabetes Care. 12(9), 604–608. doi:10.2337/diacare.12.9.604

20. American Association for Clinical Chemistry. (2014). FDA proposes two sets of standards for glucose meters. Retrieved from http://labtestsonline.org/news/140313glucose-meters/

About the author

Kenny Navarro is an Assistant Professor in the Department of Emergency Medicine at the University of Texas Southwestern Medical School at Dallas. He also serves as the AHA Training Center Coordinator for Tarrant County College. Mr. Navarro serves as an Emergency Cardiovascular Care Content Consultant for the American Heart Association, served on two education subcommittees for NIH-funded research projects, as the Coordinator for the National EMS Education Standards Project, and as an expert writer for the National EMS Education Standards Implementation Team. Send correspondence concerning any articles in this section to Kenneth W. Navarro, The University of Texas Southwestern Medical School at Dallas, 5323 Harry Hines Blvd MC 8890, Dallas, Texas 75390-8890, or e-mail kenny.navarro@ems1.com.

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