Glucose monitoring options in dogs and cats

The next time you receive a diabetic patient, remember there are several choices for monitoring available

Figure 1: Jugular blood sampling in feline patient.
Photo courtesy, 2016.

More and more frequently, our patients are benefiting from a world of advancing technology to treat various ailments.

Diabetes mellitus in dogs and cats can be challenging to treat and difficult to monitor due to the stress of hospitalization, nervous pet parents attempting to manage the disease for the first time, and supply shortages. Then there is the cost associated with insulin, syringes, and monitors.

Let us look at several methods used to monitor diabetes treatment in cats and dogs, and how new technological advances in human medicine have been used to help our veterinary patients.

An essential component to managing diabetes in our patients is knowing how their bodies react to food, and insulin when regulating blood glucose levels.

There are several methods available to monitor a patient’s response to food and insulin. They measure the blood sugar or enzyme levels directly from a blood sample or by calculating the glucose level based on interstitial fluid; each is detailed below.

Fructosamine levels

Measuring a fructosamine level requires the patient to visit the hospital for a blood sample collection. The sample is either processed in-house or sent to an off-site laboratory for testing and evaluation.

A fructosamine level will give an average of the blood glucose over the past 14 to 28 days and can be used to determine if a patient has gone into a diabetic remission. The fructosamine level is not affected by stress.

A fructosamine level does not show short-term fluctuations in blood glucose (it is an average over time). It can be misleading in some cats with a hyperthyroid comorbidity due to the increase protein turnover rate.1 AS mentioned, measuring a fructosamine level requires the patient to visit the hospital for a blood draw (Figure 1). The blood is then placed into a serum separator tube and allowed to clot. Afterwards, the sample is spun down to separate serum from blood cells and is either sent off to a laboratory for testing or run in-house with specialized laboratory equipment.

Whatever method you choose to process your samples, it is imperative to consistently use the same method for each individual patient. Running a fructosamine level in-house for one sample and then sending a follow up sample weeks to days later to an outside lab can lead to confusing results due to the difference in testing methods used.

Getting a fructosamine level is only as stressful as a quick vet visit to take a blood sample. It is less expensive than a glucose curve or serial blood glucose monitoring, and it is not affected by the patient’s reaction to stressors.

Glucose curves

Figure 2: Ear prick blood sampling form a cat.
Photo courtesy Wikihow; Jamie Freyer, DVM, 2018.

A glucose curve will determine how the blood glucose changes over time as food is digested and insulin injections react within the body. It involves multiple venous or body pokes (ear pinna, paw pad, or mucosal blood) over a 12-hour period. The blood glucose measurements the curve is generated from can be falsely elevated by the patient’s stress.

A glucose curve can be performed in the pet’s home with a highly trained pet parent and handheld glucometer (Figure 2). In-home testing with a competent pet parent is far less stressful for the patient, but it does require the person to adhere to strict feeding, medicating, and testing guidelines for accurate information. Many pet parents opt to have their pet’s diagnostics performed in the hospital by veterinary professionals.

A blood glucose curve is performed by feeding the patient its first meal then taking the first blood sample or reading just prior to the morning insulin administration. Blood samples or readings are then collected/performed every two hours throughout the day for 12 hours. The data from the blood glucose readings is graphed to create a curve or reading of blood glucose measurements throughout the 12-hour period. The veterinarian will use the blood glucose curve to evaluate the effectiveness of the current treatment plan and determine any adjustments that may needed (insulin dosage and feeding).

The blood glucose curve is one tool to create or evaluate the efficacy of the current treatment plan. In general, maintaining blood glucose levels in cats with diabetes between 120–300 mg/dL and dogs with diabetes between 100–250 mg/dL for the majority of the day will minimize the symptoms of diabetes and complications.1

If performed in the clinic, a blood glucose curve can be stressful to patients, which may lead to inaccurate blood glucose readings. This can be staff intensive and requires seven or more body pricks or venous sticks that can also be quite stressful for the patient.  The in-clinic blood glucose curve requires the patient to stay for the day, and can be quite costly for the owner (total up the hospital stay, hospital medication, seven blood glucose readings, DVM examination, and DVM testing interpretation and recommendations).

Continuous glucose monitoring

Figure 3: Continuous glucose monitor after placement on the dorsolateral thorax of a cat.
Photo courtesy Veterinary Internal Medicine Nursing, October 25, 2021

A continuous glucose monitor measures the blood glucose level in real time over a period of 10 to 14 days and updates via a scanning device or application on your phone to a cloud-based account. The monitor must be implanted by a veterinary professional familiar with the device; it involves shaving off a small patch of hair over the dorsolateral portion of the thorax, preparing the skin and either gluing or suturing the device in place.

Continuous glucose monitoring systems (or flash glucose monitoring systems) are devices designed for diabetic humans (Figure 3), which have several different types available on the market. The monitor must be prescribed by a veterinarian and purchased from a pharmacy.

In general, a continuous glucose monitor is constructed with an adhesive sensor (roughly 3-4 cm in diameter) that contains a small probe. This probe sits underneath the skin and constantly measures the glucose levels in the interstitial fluid. The sensor is read using either a smartphone application or a dedicated reader (a small device that looks like a glucometer). According to a 2019 article,7 each sensor lasts for up to 14 days, and data from the sensor needs to be downloaded to the reader or phone application at least once every eight hours because each sensor can only store eight hours’ worth of data at any time. The device measures interstitial glucose levels, rather than blood glucose.

“There is a small difference in this measurement as compared to the amount of glucose in the blood, but for the purpose of monitoring your patient’s diabetes that difference is negligible.”3

There is the possibility that rapid fluctuations in glucose levels might be missed by the reader. “The flash systems are sometimes not as consistently reliable for pets as they are for humans.”3

If the flash system indicates that your patient’s glucose level is low and your patient is not having signs of low blood glucose (trembling, weakness, panting, seizures, collapse etc.), you should check your patient’s blood glucose with a standard veterinary glucometer to confirm low blood glucose before attempting to counteract the hypoglycemia.

If your patient is having signs of hypoglycemia and the flash system is registering a normal glucose level, you should also double-check the flash system against a standard glucometer.

It is important the patient be properly hydrated; dehydration will negatively affect the accuracy of the readings.  Application in euhydrated patients, or correction of any dehydration before sensor application, is recommended.

A continuous glucose monitor can be less stressful for the patient, more cost efficient for the client, and less time intensive for hospital staff. It involves only a short visit and application as described above and can be monitored at home by the pet parent.

The next time you receive a diabetic patient, remember, you have several choices for monitoring available and can advocate for the best option for your patient.

Allyne Moon has been working in veterinary medicine since 1992. She received her LVT license in 2003; her RVT license in 2004, is an expert witness for the State of California, and is a former VMB yospital inspector. Moon lectures nationally and locally on a variety of subjects, including veterinary forensics, shelter medicine, radiation safety, suicide prevention, compassion fatigue, and veterinary law. Her love for animals led her to work for an open-admission municipal animal shelter in Southern California, treating a wide variety of animals and conditions ranging from upper respiratory infections to gunshot wounds and vehicular trauma. She now works as the assistant executive director of the Southern California Veterinary Medical Association.


    1. Glycated Protein Levels- Merck Animal Health USA (
    2. Use of the “FreeStyle Libre” glucose monitoring system in diabetic cats.  Verng Deiting, Reinhard Mischke Research in Veterinary Science vol. 135, March 2021, 253-259:
    3. Flash Glucose Monitoring with FreeStyle Libre in Cats and Dogs. Margaret Hammond-Lenzer, DVM; Sherri Wilson, DVM, DACVIM; Brett Wasik, DVM, DACVIM Veterinary Partner (VIN) 22 March 2019:
    4. Evaluation of sensor sites for continuous glucose monitoring in cats with diabetes mellitus PubMed ( J Feline Med Surg. 2013 Feb;15(2):117-23.  doi: 0.1177/1098612X12463925. Epub 2012 Oct 12.
    5. Use of the “FreeStyle Libre” glucose monitoring system in diabetic cats. Verena Deiting, Reinhard Mischke Research in Veterinary Science. 2021 March, 253-259:
    6. Accuracy of a continuous glucose monitoring system in dogs and cats with diabetic ketoacidosis. Reineke EL, Fletcher DJ, King LG, Drobatz KJ. J Vet Emerg Crit Care (San Antonio). 2010 Jun;20(3):303-12. doi: 10.1111/j.1476-4431.2010.00538.x.PMID: 20636983:
    7. Flash Glucose Monitoring with FreeStyle Libre in Cats and Dogs. Margaret Hammond-Lenzer, DVM; Sherri Wilson, DVM, DACVIM; Brett Wasik, DVM, DACVIM  Veterinary Partner (VIN) 22 March 2019:
    8. Serum Fructosamine and Glycosylated Hemoglobin. Glycated Protein Levels | Merck Animal Health USA (

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