continuous glucose monitoring

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Continuous Glucose Monitoring

Glucose monitoring has come a long way, from dipstick measurements of urine

glucose, to portable blood glucose meters and strips, to the present era in

monitoring: continuous glucose monitoring or " CGM. "

Using the evolving CGM technology, people can now move beyond that

" snapshot " analogy outlined earlier in the chapter, into an era of " video "

perspectives on glucose patterns -- truly watching the patterns of glucose

rise and fall during the day, and seeing the influence of the various

factors that can affect glycemic control.

CGM has made its own advancements from retrospective to real-time (RT) CGM.

Retrospective, or professional CGM, still has a role in diabetes management,

however. Professional CGM is geared towards clinical use. It's meant to be

used for brief periods of time to assist the clinician and the patient in

fine-tuning the diabetes treatment plan, especially when information from

blood glucose meter readings and A1C aren't sufficient in and of themselves

to pinpoint problem areas, such as overnight hypoglycemia, for example. With

professional CGM the results are blinded to the patient; results are only

available after downloading the device. For patients who desire to

continuously monitor and refine their diabetes management, RT-CGM (or

patient CGM), is now available. It's expected that RT-CGM will revolutionize

diabetes management for providers and patients alike. A key feature of

RT-CGM is its ability to alert the patient, via trending arrows and alarms,

to impending hypo- and hyperglycemia; the patient is then in a better

position to take necessary measures to prevent glucose levels from dropping

or rising further.

Indications for both professional and patient CGM include frequent

hypoglycemia, hypoglycemia unawareness, elevated A1C despite multiple

adjustments in the treatment plan, frequent visits to the emergency room or

hospital due to issues with glycemic control, pregnancy and presence of

diabetes complications that may be impacting glycemic control (e.g.,

gastroparesis). Insurance coverage for RT-CGM is limited and is mainly

approved for those patients with documented glycemic control issues. Also,

at this time, RT-CGM is primarily used by patients on physiologic insulin

regimens.

RT-CGM uses a disposable sensor that measures interstitial glucose every few

minutes continuously, over the course of 24 hours. The patient inserts the

sensor just underneath the skin and the sensor must be replaced every three

to seven days. Attached to the sensor is the transmitter; this sits on top

of the skin and relays glucose readings from the sensor to the receiver. The

receiver is a small, pocket-sized device that receives and displays glucose

readings from the transmitter. All CGM devices have software that enables

both the patient and the healthcare team to download reports. These reports

can be invaluable to guide the provider in making treatment plan decisions

with the patient.

As more and more patients begin using RT-CGM, it's important for the

healthcare provider to understand an important distinction between this

technology and SMBG. A blood glucose meter measures capillary glucose,

whereas a CGM sensor measures interstitial glucose. Because of this, SMBG

and sensor readings may vary. It can take up to 30 minutes for glucose to

pass from capillary blood into interstitial fluid. This delay is known as

" sensor lag. " This does not mean that the sensor is inaccurate, but it does

mean that the patient needs to base treatment decisions, such as insulin

boluses or hypoglycemia treatment, on fingerstick readings rather than

sensor readings.

Provider and patients alike must have realistic expectations of RT-CGM.

While RT-CGM provides minute-by minute readings of glucose levels and alerts

for high and low glucose, and displays glucose fluctuations and trends that

are missed with intermittent SMBG, at this time, it does not eliminate the

need for SMBG, nor does the continuous glucose monitor make treatment

decisions. In addition, both the provider and the patient must understand

the device's technology, along with its subsequent limitations, such as

possible issues with sensor adherence, skin irritation and bleeding, and the

potential tendency for patients to overreact to high readings seen on their

receiver by overbolusing insulin. Finally, patients (and clinicians!) must

be prepared for the seemingly overwhelming amount of information that a CGM

device provides. Patients now have numerous glucose readings 24 hours a day

rather than the usual four fingerstick readings obtained from a blood

glucose meter. Initial excitement can quickly turn to frustration and

anxiety unless realistic expectations are discussed prior to using RT-CGM.

The diabetes care team plays an important role in guiding patients to

properly use RT-CGM and interpret results, with the end result being

improved diabetes management. This is a process that requires expertise,

time and patience for all involved.

Clinicians interested in using either retrospective or RT-CGM with their

patients have the option of initiating CGM in their own office, or referring

their patients to a diabetes center. Patients must first determine coverage

through their health plan. Also, a letter of medical necessity and

documentation of clinical need for CGM is required from the patient's

physician. CGM requires training and education, and given time and resource

constraints, it may be expeditious to refer patients to a local diabetes

program or contract with a local diabetes educator who is trained in CGM to

come to the office to initiate the training. The CGM device companies can

also provide training, albeit more of the " technical " aspects of training,

such as how to insert a sensor and how to set alarms. Company

representatives generally do not provide diabetes education and treatment

plan adjustment around the results; result interpretation is a critical

component of CGM use and should be provided by qualified clinicians.

-Interpreting CGM

Interpreting the glucose patterns obtained through CGM takes practice, and

the more you do the more adept you become. Generally, an approach would be

to view 3-7 days of data at one time. Trying to absorb more than that in one

review is not helpful and may be overwhelming.

As you look over the data, think about factors that may lead to high and low

glucose. Low glucose may be caused by too much insulin, too little food,

unexpected or unplanned physical activity, and alcohol. Factors that may

lead to high glucose include too little insulin, too much food, not enough

physical activity, illness, and stress. Then, look for lows or highs that

occur at the same times on different days and ignore one-time, single

excursions that may not reflect patterns. As you would when looking at blood

glucose log books, look for patterns (when multiple lines are closest

together on the report). Focus on addressing the lows first, starting with

overnight and then progressing throughout the day, and try to fix those

problems initially.

For example, many of the glucose " excursions " will be food related; this

entails possibly adjusting the I:carb ratio, reinforcing more precise

carbohydrate counting, choosing lower glycemic index foods and/lower fat

foods, use of alcohol, etc. Also, the correction factor may need adjusting,

or patients may need to learn how to adjust insulin for exercise, for

example, if lows are an issue. Involve the patient and inquire as to why

they think they are spiking or going low, and then review possible treatment

options, such as choosing a breakfast with a lower glycemic index.

As the use of these devices becomes more widespread, educational programs to

further support the development of skills in using and interpreting results

from these devices will undoubtedly be developed. Until that time, if you

have a patient who would benefit from the use of CGM but you and your

practice do not have the time and resources to develop the capabilities to

mange it yourself, referral to a diabetes specialty center might be the best

option. Through these consultative interactions, you will begin to learn

more about the use and interpretation of this new technology which might

help with the development of your own capabilities in this area at some

point in the future.

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