October 09, 2018
3 min read

FDA-cleared blood glucose monitors not always accurate

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In a series of tests, only six of 18 blood glucose monitoring systems that have been cleared by the FDA consistently delivered levels of accuracy based on international and U.S. regulatory standards, according to findings published in Diabetes Care.

“Many patients complain that their blood glucose monitor system is not accurate,” David C. Klonoff, MD, FACP, FRCP, medical director of the Diabetes Research Institute at Mills Peninsula Medical Center in San Mateo, California, told Endocrine Today. “We conducted a study with a consensus protocol for testing and metrics of accuracy that were developed by an expert panel consisting of leading clinicians, clinical chemists, patient advocates, statisticians and government regulators from FDA, CDC and NIH. We tested the leading selling 18 [blood glucose monitors] that comprise 90% of the U.S. market. Only 12 of these 18 consistently performed accurately to the standard for which they were approved. This was the largest accuracy study of FDA-cleared [blood glucose monitors], using a consensus protocol created with input from the FDA, ever reported in the literature.”

From 2016 to 2017, researchers recruited 1,035 adults with type 1 diabetes, type 2 diabetes or prediabetes to have a capillary blood glucose level measured on six different blood glucose monitoring systems as well as a reference capillary sample prepared for plasma testing at a reference laboratory (mean age, 51.5 years; 54.1% women).

Systems came from consumer outlets and were tested in three triple-masked studies with each of three participating clinic sites testing a different set of six systems for each of the three studies. On average, each blood glucose monitor was tested by 115 participants, according to the researchers.

Researchers defined a compliant blood glucose result as within 15% of a reference plasma value for blood glucose at least 100 mg/dL or within 15 mg/dL for blood glucose of less than 100 mg/dL.

The proportion of compliant readings (measured as the total compliant readings out of total readings) in each study was then compared against a predetermined accuracy standard that was similar to current regulatory standards.

Researchers also considered other metrics of accuracy, including the overall compliance proportion, the proportion of extreme outlier readings differing from the reference value by more than 20%, modified Bland-Altman analysis (average bias, coefficient variation and 95% limits of agreement) and, as determined by the Surveillance Error Grid, the proportion of readings with no clinical risk.

Researchers found that blood glucose monitor rankings remained similar regardless of which accuracy metrics were analyzed, with six of the 18 systems meeting the predetermined accuracy standard in all three studies: Contour Next (Bayer, now known as Ascensia), Accu-Chek Aviva Plus (Roche), Walmart Reli-On Confirm Micro (Arkray), CVS Advanced (AgaMatrix), FreeStyle Lite (Abbott Diabetes Care) and Accu-Check SmartView (Roche). Five monitors met the accuracy standard in two studies, three met it in one study and four did not meet the accuracy standard in any of the three studies.


The six top-performing blood glucose monitors based on the accuracy standard also met the four additional metrics, whereas the 12 lower-ranking blood glucose monitors demonstrated a wide array of overall performance with an overall compliant proportion ranging from 71% to 92%.

The researchers concluded that, in some cases, blood glucose monitors may result in treatment errors when patients depend on accurate results to determine treatment, according to Klonoff.

“There is a role for post-market testing of some products, like [blood glucose monitors], after these products are cleared by FDA and are on the market,” Klonoff said. “Their performance in the real world might, in some cases, be different from what it was at the time the product was originally tested for clearance purposes. The FDA needs to be granted more authority from the U.S. Congress to remove poorly performing products from the marketplace after they are cleared.” – by Melissa J. Webb

Disclosures: The study was supported by a grant from Abbott Diabetes Care. Klonoff reports he is a consultant for Ascensia, AstraZeneca, EOFlow, Intarcia, Lifecare, Novo Nordisk and Voluntis; has received research funding from Diasome, Lexicon and Novo Nordisk; and is an employee of the Diabetes Technology Society. Please see the study for all other authors’ relevant financial disclosures.

Editor’s note: This article was updated on Oct. 10 to correct the name and manufacturer of the Contour Next monitor.