CGM a useful tool for tracking blood glucose in real time

Q: My best friend has diabetes. She used to do finger sticks, but now she has a wearable glucose monitor. How do they work? It's got me wondering if it might be a good idea for me to use one, too. I'm 66 years old, and as I'm getting older, I worry more about developing Type 2 diabetes.

A: Your question gives us an opportunity to address an error that appeared in a recent column in which we discussed blood-sugar control. It occurred due to an edit that was made during the publishing process, and was brought to our attention by a reader in Nebraska. (Thank you.) The correct information is that the risk of developing Type 2 diabetes, as well as prediabetes, increases with advancing age.

The data show that people who are 45 or older, are overweight or obese, are sedentary, or who have a family history of diabetes are at increased risk of developing Type 2 diabetes. Other contributing factors include poor diet, poor sleep and metabolic issues tied to insulin resistance.

With all of this in mind, your concern about keeping your blood sugar within a healthy range is well-founded. And that brings us to the subject of your question.

A continuous glucose monitor, also known as a CGM, is a wearable medical device that allows someone to track their blood-sugar levels in real time. A tiny filament implants into either the upper arm or the belly and sits in the tissues just below the skin. It's attached to a wireless transmitter that sends the collected data to the device. Depending on the brand of the device, that data can be read on a cellphone app, a smartwatch or a dedicated receiver.

Some CGM devices can be applied by the user at home. Others require a visit to a health care professional. The length of time a sensor is meant to remain embedded ranges from a few days to a few months, again depending on the specific device.

The sensor in a continuous glucose monitor measures glucose levels in the cellular fluid where it is implanted. Unlike a finger stick, which requires a separate test for each new data point, a CGM lets you track your blood-glucose levels in real time. That means you're easily able to see how your body responds to different foods, periods of fasting and various types and levels of activity.

With multiple data points, a CGM offers a more complete picture of how your body manages blood sugar throughout the day and night. And while these devices can greatly reduce the need for finger sticks, they have not yet completely replaced them. Blood-based glucose readings are the gold standard for accuracy. They continue to be recommended for CGM users, tailored to each person's individual health and needs.

Although most CGM users have diabetes, we sometimes recommend the 14-day variety for certain non-diabetic patients as a one-time learning exercise. Seeing how specific foods and activities affect blood sugar teaches them to make more informed choices. Your own doctor can help you decide if this would be useful for you.

Q: Each time I have a mammogram, I'm told it's not readable because of dense breast tissue. If these painful scans don't serve a purpose, wouldn't I be better off just doing self-exams and alerting my doctor of anything unusual? Is there any help for women with dense breast tissue?

A: Thank you for bringing up an important issue that affects many women. It is estimated that at least 45% of women have dense breast tissue. The term is used when a high percentage of so-called dense tissues are present in the breast. This includes the lobes and ducts, which are glandular tissues that produce and carry milk, and the network of fibrous connective tissue that supports the breasts.

Levels of breast density are often rated on a scale of A to D. They range from almost entirely fatty, scattered density, moderately dense and extremely dense. Research has uncovered a genetic link to breast density. However, additional factors, such as age, body mass, menopause and the use of hormone-replacement therapy, have been shown to also play a role.

Breast density is significant for two reasons. One is that, as has occurred in your case, the presence of a high ratio of dense-to-fatty tissue affects the results of a standard mammogram. X-rays pass through fatty tissue, which appears as dark areas on a mammogram. Fibrous and glandular tissues absorb X-rays and appear as white areas. But so do potential tumors. When someone has dense breasts, it can be difficult to differentiate between healthy tissue and a tumor. That means the small, early-stage tumors these scans are meant to catch may be missed. At the same time, the data show there is a higher risk of breast cancer in women with dense breast tissue. The reason for this is not yet understood, but it makes successful scans even more important.

When one of our patients has breast tissue that is dense enough to obscure the results of a mammogram, we often recommend they follow up with a scan known as 3-D tomography. Also referred to as a 3-D mammogram, this technique produces multiple images of the breast, which are taken from numerous angles. These digital images, which are made up of 1 millimeter "slices," are then compiled into a 3-D image. This makes it easier to visualize the interior of the breast and to identify potential abnormalities.

If a 3-D mammogram still fails to produce a useful image, then ultrasound or MRI studies may be used. High-risk breast cancer patients who undergo more frequent scans often alternate mammography with MRI. Ultrasound can also be an option for women who absolutely refuse to have a mammogram due to radiation exposure. It's also often used as a follow-up tool when an initial mammogram shows areas of concern.

Breast cancer screening is a very effective tool. We urge you not to give up on it. Speak with your doctor regarding your situation, and tell him or her you want to receive scans that are appropriate for dense breast tissue.

• Dr. Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr. Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu.