This has been an area of considerable controversy. Various studies have given conflicting results. Those studies have been criticized for various flaws: some were retrospective, non-randomized, not designed to rule out confounding factors, high drop-out rate, subjects already had well-controlled diabetes, etc. A systematic review showed no benefit from monitoring. So a new prospective, randomized, controlled, community based study was designed to help resolve the conflict.
O’Kane et al studied 184 newly diagnosed patients with type 2 diabetes who had never used insulin or had any previous experience with blood glucose monitoring. They were under the age of 70 and recruited from community referrals to hospital outpatient clinics, so they were likely representative of patients commonly seen in practice. They were randomized to monitoring or no monitoring. Patients in the monitoring group were given glucose meters and were instructed in their use and in appropriate responses to high or low readings, such as dietary review or exercise. They were asked to take four fasting and four postprandial readings every week for a year. Patients in the no monitoring group were specifically asked NOT to acquire a glucose monitor or do any kind of self-testing. Otherwise, the two groups were treated alike with diabetes education and an identical treatment algorithm based on HgbA1C levels.
We were unable to identify any significant effect of self monitoring over one year on HbA1c, BMI, use of oral hypoglycaemic drugs, or reported incidence of hypoglycaemia. Furthermore, monitoring was associated with a 6% higher score on the well-being depression subscale.
So home monitoring not only did no good but it made patients feel worse. Why? Perhaps because they were constantly reminded that they had a disease and worried when blood glucose levels rose, especially when the recommended responses of dietary review and exercise didn’t rapidly lead to lower readings.
We would not accept the results of one isolated study without replication, but in this case the new study adds significantly to the weight of previous evidence and arguably tips the balance enough to justify a change in practice.
The American Diabetes Association still says “Experts feel that anyone with diabetes can benefit from checking their blood glucose.” But they only recommend blood glucose checks if you have diabetes and are:
• taking insulin or diabetes pills
• on intensive insulin therapy
• having a hard time controlling your blood glucose levels
• having severe low blood glucose levels or ketones from high blood glucose levels
• having low blood glucose levels without the usual warning signs
Diabetes experts see the severe, complicated cases and have a different perspective from that of the family physician seeing mostly mild and uncomplicated cases. An article in American Family Physician said
Except in patients taking multiple insulin injections, home monitoring of blood glucose levels has questionable utility, especially in relatively well-controlled patients. Its use should be tailored to the needs of the individual patient.
An editorial in the BMJ pointed out that
Home blood glucose monitoring is a big business. The main profit for the manufacturing industry comes from the blood glucose testing strips. Some £90m was spent on testing strips in the United Kingdom in 2001, 40% more than was spent on oral hypoglycaemic agents.2 New types of meters are usually not subject to the same rigorous evaluation of cost effectiveness, compared with existing models, as new pharmaceutical agents are.
If the scientific evidence supporting the role of home blood glucose monitoring in type 2 diabetes was subject to the same critical evaluation that is applied to new pharmaceutical agents, then it would perhaps not have been approved for use by patients.
Home glucose monitoring in type 2 diabetes is not justified by the evidence. It does not improve outcome, it is expensive, and it may decrease the quality of life of patients.
Common sense suggested monitoring should improve outcome. We had assumed it would work. Scientists thought to question that assumption. The found a way to test that assumption. New evidence showed that it was a false assumption. In response to that evidence, the practice is now being abandoned. This is how science is supposed to work. Another small triumph for science-based medicine.
This article was originally published in the Science-Based Medicine Blog.