Home Monitoring of Blood Glucose in Cats with Diabetes Mellitus

CHAPTER 26 Home Monitoring of Blood Glucose in Cats with Diabetes Mellitus



Claudia E. Reusch, Nadja S. Sieber-Ruckstuhl



CHAPTER OUTLINE


Monitoring in the Hospital 274

Self-Monitoring of Blood Glucose in Human Beings with Diabetes Mellitus 276

Home Monitoring of Blood Glucose by Cat Owners 276
Blood Sampling Techniques 276

Portable Blood Glucose Meter 278

Introduction of Capillary Blood Glucose Measurement to Cat Owners 279

Problems Encountered in Home Monitoring 280

Interpretation of Blood Glucose Curves Generated at Home and Comparison of Home and Hospital Blood Glucose Curves 280

Long-Term Compliance with Home Monitoring 281

Continuous Glucose Monitoring Systems 282

Case Example 1 282

Case Example 2 283

Diabetes mellitus is a common endocrine disease in cats. A recent study reported an increase in hospital prevalence over 30 years from 0.08 per cent in 1970 to 1.2 per cent in 1999.1 Currently it is assumed that approximately 80 per cent of these cats suffer from type 2–like diabetes, which is characterized by a combination of insulin resistance by peripheral tissues and liver and of β-cell failure. High blood glucose itself has negative effects on β-cell function and insulin sensitivity, a phenomenon called glucose toxicity. Immediate treatment may reverse these effects, at least in part, and the diabetes may go into remission. Remission usually occurs during the first 3 months of therapy; however, it may take 1 year or longer.2 The possibility of diabetic remission is one of the reasons why close supervision and regular measurement of blood glucose is paramount. If remission occurs unnoticed and the administration of insulin is not discontinued, serious hypoglycemia may result.


The aim of therapy is to provide a good quality of life by eliminating clinical signs of diabetes (achieve remission, if possible), and by preventing complications such as hypoglycemia and ketoacidosis. Achieving normal blood glucose levels is not necessary, because most cats do well when the blood glucose concentration is maintained between 90 and 270 mg/dL.


Successful treatment requires that the owner be highly motivated and collaborate closely with the veterinarian, who should follow a precise protocol. Box 26-1 gives a brief overview of the protocol used in our hospital.



Box 26-1 Treatment and Management Protocol for Cats with Uncomplicated (Nonketotic) Diabetes Mellitus Used at the University of Zurich, Switzerland



AT THE TIME OF DIAGNOSIS



• Diagnosis (hyperglycemia, glucosuria, increased fructosamine) and evaluation for concurrent diseases (e.g., urinary tract infection [urine culture], hyperthyroidism [T4], pancreatitis [abdominal ultrasonography, fPLI]).

• Cessation of diabetogenic drugs if possible.

• Start insulin therapy with intermediate-acting insulin (Caninsulin/Vetsulin or glargine, 1 to 2 U/cat q12h, depending on body weight and degree of metabolic derangement (i.e., severity of clinical signs, degree of hyperglycemia, and elevation of fructosamine).

• Hospitalization for 1 to 2 days.

• Measurement of blood glucose 3 to 4×/day (approximately every 4-6 hours); decrease insulin dose (by 25-50 per cent) if blood glucose drops by <90 mg/dL and reevaluation if dosage decrease was sufficient on the following day.

• Discharge after demonstration of injection techniques, with detailed written instructions; recommendation of high-protein, low-carbohydrate diet; weight loss if overweight. Possibility of home monitoring (HM) is mentioned.


RECHECK IN HOSPITAL 1 WEEK AFTER DIAGNOSIS



• History, body weight, physical examination.

• Blood glucose curve over 10 to 12 hours (insulin and food given at home, blood glucose measured every 1-2 hours). Fructosamine measurement.

• Adjustment of insulin dose if required (increments of 0.5-1 U/injection).

• HM and its advantages are discussed with the owner.


RECHECK IN HOSPITAL 3 WEEKS AFTER DIAGNOSIS



• History, body weight, physical examination, blood glucose curve, fructosamine measurement, dose adjustment (as after 1 week).

• Introduction to home monitoring of blood glucose if owner is interested.


HOME MONITORING OF BLOOD GLUCOSE BY THE OWNER



• Measurement of fasting capillary blood glucose 2×/week.

• Generation of 12-hour capillary blood glucose curve (measurement of glucose every 2 hours), 1×/month.


RECHECK IN HOSPITAL 6 TO 8 WEEKS AFTER DIAGNOSIS



• History, body weight, physical examination, blood glucose curve, fructosamine measurement, dose adjustment (as after 1 week).

• Reassessment of home monitoring techniques (if performed).

• Tests for underlying diseases if clinical suspicion (e.g., hypercortisolism, hypersomatotropism).


RECHECK IN HOSPITAL 10 TO 12 WEEKS AFTER DIAGNOSIS



• History, body weight, physical examination, blood glucose curve, fructosamine measurement, dose adjustment (as after 1 week).

• Reassessment of home monitoring techniques (if used).


FURTHER RECHECKS IN HOSPITAL EVERY 4 TO 6 MONTHS



• History, body weight, physical examination, blood glucose curve, fructosamine measurement, dose adjustment (as after 1 week).

• Reassessment of home monitoring techniques (if used).

• Urine culture once a year.


MONITORING IN THE HOSPITAL


Home monitoring (HM) of blood glucose by owners is an additional tool to improve long-term management of diabetes. However, it does not replace regular reevaluation by a veterinarian. The latter should include assessment of clinical signs and determination of serum fructosamine and blood glucose concentrations. The assessment of clinical signs by both owner and veterinarian is the most important parameter. A well-regulated cat has no or only very mild clinical signs of diabetes. In a cat with no clinical signs it is crucial to determine whether diabetic remission has occurred. In cats with persistent clinical signs, the cause must be identified and therapy optimized accordingly.


Fructosamine is the product of an irreversible reaction between glucose and the amino groups of various serum proteins, and its concentration reflects the mean blood glucose concentration of the preceding 1 to 2 weeks. Reference ranges differ slightly among laboratories but usually are around 200 to 360 µmol/L. In most cats with newly diagnosed diabetes, fructosamine levels are higher than 400 µmol/L and may be as high as 1500 µmol/L. Normal fructosamine levels may be seen in cats with a very recent onset of diabetes and in diabetic cats suffering from concurrent hyperthyroidism or hypoproteinemia.3–5 Fructosamine concentrations increase when glycemic control worsens and decrease when glycemic control improves. Because even well-controlled cats are slightly to moderately hyperglycemic throughout the day, fructosamine concentration usually will not decrease into the normal range. Accordingly a normal fructosamine concentration (particularly a fructosamine value in the lower half of the reference range) should raise concern about prolonged periods of hypoglycemia (e.g., insulin overdose, diabetic remission).


In general metabolic control is considered good when fructosamine levels are between 350 and 450 µmol/L, moderate when values are between 450 and 550 µmol/L, and poor when levels are higher than 550 to 600 µmol/L. In the latter case, fructosamine is not helpful in characterizing the problem because all of the possible reasons for poor regulation (e.g., insulin underdose, too short a duration of insulin effect, diseases causing insulin resistance, insulin absorption problems, Somogyi effect) have the same impact on fructosamine. In some cats fructosamine levels remain high, suggesting poor metabolic control, although clinical signs and blood glucose levels are well-controlled. The reason for this discrepancy in most cats remains unknown. Therefore the assessment of clinical signs and blood glucose concentration are the most important criteria for treatment decisions.


Blood glucose curves (BGCs) are necessary to assess insulin efficacy, glucose nadir, duration of insulin effect, degree of blood glucose fluctuation, and the Somogyi effect. In general single glucose measurements are considered insufficient to assess metabolic control.


Evaluation of BGCs is of particular importance in the initial phases of diabetic regulation and in cats with persistence of clinical signs. For performance of an in-hospital BGC we prefer that owners give insulin and food at home, and then bring the cat to the hospital as soon as possible (within 2 hours). This approach eliminates the effect of lack of food intake on blood glucose levels if the cat refuses to eat in the clinic, at least in those cats who are only fed at the time of insulin administration. Only when technical difficulties are suspected are owners asked to bring the cat to the hospital before insulin administration and to carry out the entire injection procedure under supervision. Different approaches may be more appropriate depending on the circumstances; for instance, when the distance between the cat’s home and the hospital is very long.


BGCs are generated by measuring the glucose concentration every 1 to 2 hours throughout the day until the next insulin dose is due. In our hospital, we avoid multiple venipunctures by collecting capillary blood from the ear using the same sampling technique and the same portable blood glucose meter (PBGM) as cat owners at home (see later).


Until recently BGCs were only created in the hospital because most owners are not skilled in collecting venous blood samples. However, there are several problems associated with serial blood glucose measurements in hospitalized cats. First, the procedure is time consuming and expensive; therefore in many patients it may not be carried out as often as indicated. Second, the concentration of blood glucose can be influenced markedly by stress or lack of food intake. Cats in particular are sensitive to stress caused by veterinary manipulation in an unfamiliar environment. Consequently the BGC may show a continual increase in glucose concentration or it may be elevated from the beginning. In the latter situation it is not possible to differentiate between stress-associated hyperglycemia, insulin underdose, and the many causes of insulin resistance. In cats who are brought to the hospital to generate a BGC before feeding or in cats who are used to nibbling food throughout the day, refusal to eat has a serious impact on blood glucose concentration. It is then difficult to decide whether lack of food intake or insulin overdose is the cause of low glucose concentrations.



SELF-MONITORING OF BLOOD GLUCOSE IN HUMAN BEINGS WITH DIABETES MELLITUS


In the late 1970s self-monitoring of blood glucose (SMBG) was introduced in human medicine.6–8 For SMBG human patients obtain a drop of capillary blood, usually by pricking a fingertip, with the aid of a lancing device. The drop then is placed on a test strip, and the glucose concentration is measured using a PBGM. The sampling process is simple and has become relatively painless with the use of newer generations of lancing devices. The introduction of SMBG is regarded as the single most important advance in the management of diabetes since the discovery of insulin.9 Today all diabetes treatment guidelines include SMBG as an integral part. Diabetic individuals (type 1 and 2) treated with insulin are advised to perform SMBG several times daily, and regular monitoring also is recommended in diabetics treated with oral hypoglycemic drugs or diet only.10 More frequent SMBG is associated with better metabolic control, which in turn decreases the incidence and slows the progression of complications of long-standing diabetes.9,11–13 SMBG has made it possible for patients to obtain immediate and precise feedback on their blood glucose concentration, allows them to understand the impact of food choices, physical activity, and concurrent illness, and gives them control of their disease.


Patients conducting SMBG need guidance and supervision because user technique is the major source of errors. All authorities recommend that each patient’s monitoring technique be evaluated initially and at regular intervals thereafter. Patients also need to be taught how to use the data to adjust food intake, exercise, or drug therapy.


For human beings who find pricking a fingertip unpleasant, alternative site testing has been developed. Those sites where pricking may be less painful include the upper arm, forearm, base of the thumb, tip of the earlobe, and the thigh. Blood glucose levels obtained from alternative sites may differ slightly from those obtained from the fingertips.14,15



HOME MONITORING OF BLOOD GLUCOSE BY CAT OWNERS



BLOOD SAMPLING TECHNIQUES


Until a few years ago SMBG in diabetic pets was not thought to be feasible. However, several methods have been developed recently to obtain capillary blood by means of lancing devices manufactured for human patients. In 2000 two methods of capillary blood sampling from the ear were described.16 One method, which used a conventional lancing device after prewarming the ear with a hair dryer, was applicable only to dogs. The other method, the “Vaculance method,” was based on a new type of lancing device introduced at that time, the Microlet Vaculance (Bayer Diagnostics, Basel, Switzerland), and it was applied successfully in cats as well as in dogs (Figure 26-1). After lancing the skin the device creates a negative pressure, which enables the sampling of an adequate amount of blood in most instances. The details of the procedure for the Vaculance method are as follows. The tip of the ear is held between the thumb and index finger and the entire surface of the outer pinna is held flat using the remaining fingers of the same hand. With the other hand the lancing device is lightly placed on a nonhaired area of the inner pinna, such that an airtight seal is formed between the end cap of the device and the skin. When the plunger cap of the device is pressed, a lancet moves quickly back and forth one time. Pressure between the end cap and the skin is maintained while the plunger is slowly released. Because of the developing negative pressure, the skin of the ear begins to bulge into the end cap. The formation of a drop of blood is hastened by releasing the pressure exerted by the fingers on the outer surface of the pinna. When an adequate amount of blood appears on the skin, the plunger is pressed down to release the negative pressure and the lancing device is removed. Then the test strip of the PBGM is brought into contact with the blood drop and the required amount of blood is absorbed automatically (Figure 26-2).


image

Figure 26-1 Lancing device Microlet Vaculance (Bayer Diagnostics).


image

Figure 26-2 Capillary blood sampling from the ear using the lancing device Microlet Vaculance. A, Placing the lancing device on a nonhaired area of the pinna. B, Pressing the plunger cap of the device to move the lancet back and forth. C, Slowly releasing the plunger to develop a negative pressure between the end cap and the skin. D, Absorption of the blood drop by the test strip of the PBGM.


The buccal mucosa has been described as another site for capillary blood sampling in dogs.17 This site probably is not feasible in cats. Gums, lips, and footpads also have been mentioned as possible puncture sites,18 but there are no studies that have investigated their suitability in cats. It is not known whether blood glucose levels vary with different sampling sites in cats, as is the case in human beings.


An alternative to capillary sampling is the collection of venous blood from the marginal ear vein. This technique, called the marginal ear vein technique, has been used successfully in diabetic cats.19,20 After localization of the marginal ear vein on the edge of the pinna, the vein is either punctured with a needle or a lancing device. Thompson et al19 reported that a warm gauze sponge applied before puncture increased perfusion, and application of a thin film of petrolatum over the sampling site in long-haired cats allowed a drop of blood to form without dissipating into the fur. Van de Maele et al20 prepared the puncture site in long-haired cats by shaving a small part of the pinna to improve visualization of the vein, and by placing a hard cylinder-shaped object, such as the empty roll from bandage material, behind the ear to provide stability. Afterwards pressure is applied to the punctured area to avoid excessive bleeding.


The Vaculance method has been used exclusively in our hospital and by our pet owners for almost 10 years, and therefore we do not have experience with the marginal ear vein technique. The Vaculance method is easy to conduct, does not require warming of the ear or any other preparation of the puncture site, and generates a drop of blood within about 30 seconds. In contrast to the marginal ear vein technique, no bleeding is expected after capillary blood sampling and therefore no pressure is needed after the puncturing procedure.



PORTABLE BLOOD GLUCOSE METER


The first PBGM was the Ames Reflectance Meter, patented in 1971 by the Ames Company. It was almost 20 cm long and required a very large drop of capillary blood, strips that had to be washed and wiped after blood application, and an electrical power outlet. The blood glucose concentration was indicated by the position of a needle on a graduated scale after 60 seconds.


Since then numerous models have been developed and marketed that are smaller, lighter, faster, and easier to handle. Today the average PBGM fits in the palm of a hand, is battery powered, requires a very small amount of blood, and provides rapid results on a display screen. Modern PBGMs have a memory capacity for the last series of test results, and some allow data to be transferred to a personal computer. Certain models require coding or calibration, a process used to match the PBGM with the test strips. Usually this is done by inserting a code strip or entering a code number into the meter each time a new box of test strips is opened. If this process is carried out incorrectly, the readings can be inaccurate. In some PBGMs a “no coding technology” is used, ensuring that the correct code is set automatically any time a new test strip is inserted. This reduces the risk of inaccurate blood glucose measurements and simplifies meter handling. Most new models function on the basis of electrochemical methods; for example, glucose-oxidase measurements are converted into electrical signals. PBGMs often are available at little or no cost; however, the price of the test strips can be substantial.


In human medicine, quality control of PBGMs is of ongoing concern. Factors that may affect the results of glucose measurements include variation in hematocrit, altitude, environmental temperature and humidity, hypotension, hypoxia, and triglyceride concentration.21 The overall performance of a PBGM depends on the analytical accuracy of the unit, quality of the test strips, and proficiency of the user. The goal of the American Diabetes Association is that all measurements conducted with a PBGM be within 5 per cent of the laboratory value. However, this target is not met currently.22


In veterinary medicine the use of PBGMs has gained great popularity during recent years. They are not only an essential part of the HM procedure, but also are used frequently in veterinary hospitals for routine blood glucose measurements. However, it must be remembered that these devices have been designed for human beings, and most PBGMs currently available have not been validated for use in cats. However, a few studies have investigated the accuracy of PBGMs in cats.16,19,23–25 In two studies PBGM measurements using capillary blood were compared with glucose measurements using venous blood and a reference method.16,25


In our own study16 the PBGMs Glucometer Elite (Bayer Diagnostics) and Accu-Chek Simplicity (Roche Diagnostics, Inc., Indianapolis, IN) were evaluated. Using error grid analysis,26 all PBGM measurements were in zones A and B, which is indicative of clinically acceptable results (Figure 26-3). The Glucometer Elite was considered the easiest to operate because it has no buttons to press and turns on automatically when the test strip is inserted; it is the PBGM used in our hospital and by our pet owners. In contrast to other PBGMs, which underestimate or overestimate true blood glucose concentrations arbitrarily, the Glucometer Elite yielded underestimations consistently. In 2002 Bayer changed the brand name of their glucose monitor line, and the Glucometer Elite was renamed Ascensia Elite. Zeugswetter et al25 compared capillary blood glucose values measured by the PBGM FreeStyle Freedom (Abbott Laboratories, Abbott Park, IL) with venous blood glucose values measured by the reference method. The former were a mean of 32 mg/dL lower than the latter, and the error grid analysis showed that 96 per cent of the data measured with the PBGM were in zones A and B, and 2 per cent each were in zones C and E. Values in the latter zones are not acceptable from a clinical point of view.


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Figure 26-3 Error grid analysis for the Glucometer Elite using capillary blood. Values in zone A (clinically accurate) and zone B (benign estimate errors) are clinically acceptable. Values in zone C (unnecessary corrections), D (dangerous failure to detect) or E (erroneous treatment) are potentially dangerous and therefore not acceptable from a clinical point of view. For the Glucometer Elite all values were in zone A or B. Blood glucose values are given in mmol/L. Multiply by 18 to convert to mg/dL.


(From Wess G, Reusch CE: Capillary blood sampling from the ear of dogs and cats and use of portable meters to measure glucose concentration, J Small Anim Pract 41:60, 2000, with permission.)

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Aug 6, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Home Monitoring of Blood Glucose in Cats with Diabetes Mellitus

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