Portable blood glucose meters as a means of monitoring blood glucose concentrations in dogs and cats with diabetes mellitus

Portable Blood Glucose Meters as a Means of Monitoring Blood Glucose Concentrations in Dogs and Cats With Diabetes Mellitus John E. Stein, DVM, and Deborah S. Greco, DVM, PhD, Diplomate ACVIM

The use of portable blood glucose meters (PBGM) has become common in veterinary medicine as a rapid means of monitoring animals' blood glucose in a variety of medical conditions. These hand-held monitors allow for diagnostic and therapeutic decisions to be made quickly and relatively inexpensively using only a small amount of blood. Both in conditions resulting in hyperglycemia, such as diabetes mellitus, and in those resulting in hypoglycemia, such as sepsis or the presence of an insulinoma, veterinarians have come to rely on PBGM to provide critical information on the status of their animal patients. In particular, PBGM are frequently used to measure individual blood glucose values in an animal over a period to create a blood glucose curve when evaluating the effectiveness of insulin therapy in diabetic dogs and cats. Copyright 2002, Elsevier Science (USA). All rights reserved.

n general, automated chemistry analyzers using either hex-

I okinase or glucose oxidase methods on lithium heparinized

plasma are considered the gold standard for determining an animal's venous blood glucose concentration.1 These methods, however, require a larger volume of blood, more time to obtain results, limited availability, and increased cost. Although less invasive or longer-term blood glucose monitoring methods such as near-infrared spectroscopy and implantable glucose sensors have been investigated for use in humans, they are not yet available for veterinary use. ~ A number of "patient-side" blood glucose monitoring methods have been developed and are gaining favor in veterinary medicine including portable blood glucose meters (PBGM), point-of-care (POC) analyzers, and color test strips. Over the years, these devices have become increasingly precise and both faster and simpler to use, all while requiring as little as 3 to 5/xL of blood, depending on the model. 3 The majority of PGBM determine blood glucose measurements from a glucose oxidase enzymatic reaction between the animal's blood glucose and the PGBM test strip and require 20 to 30 seconds to perform. These devices are intended to be used with capillary blood (obtained in humans via a lancet) rather than the venous blood more commonly used in veterinary animals, but the majority of devices state that venous blood is acceptable. In cases in which

From Veterinary Teaching Hospital, Colorado State University, Fort Collins, CO. Address reprint requests to J.E. Stein, Veterinary Teaching Hospital, Colorado State University, 300 West Drake Road, Fort Collins, CO 80523. Copyright 2002, Elsevier Science (USA). All rights reserved. 1096-2867/02/1702-0000535.00/0 doi:l 0.1053/svms.2002.33041 "70

capillary blood is reqmred, a lancet can be used on the animal's pinna to obtain a sample. Veterinarians who use PBGM to assess their animals' blood glucose concentrations should be aware of the possible sources of error inherent in these devices. In addition to operator or machine error, factors such as environmental temperature and humidity, animal hematocrit, blood oxygen tension, concurrent drug administration, and plasma protein concentrations can affect the measured blood glucose results. 1-* Postprandial capillary blood glucose concentration may differ significantly from venous blood glucose concentration measurements, a situation that may apply to the monitoring of diabetic animals in particular. These devices were designed to be used in human patients within a specific hematocrit range rather than the more variable range found in many veterinary animals as a result of species differences and concurrent disease. Blood glucose measurements when using PBGM have been shown to be significantly higher in anemic animals, for example. Additionally, hemoconcentrated individuals, such as the relative polycythemia seen in severely dehydrated animals (i.e., diabetic ketoacidosis), or those with absolute polycythemia, may register artifactually low blood glucose concentrations with PBGMs. This effect of animal hematocrit is thought to be due to a change in the diffusion rate of plasma to the test strip reagent pad with abnormal numbers of red blood cells present, and is a potentially important consideration when evaluating the measurement of blood glucose in animals with illnesses resuhmg m abnormal packed cell volumes. Though none of the portable blood glucose meters designed for home use are currently approved for use in pets by the Food and Drug Administration (FDA), the FDA sets standards which the makers must meet for their use in humans. The American Diabetic Association also sets strict standards, though these are industry recommendations rather than legal requirements. Additionally, Canada and some other nations have their own guidelines and regulations. Although an international standard has been discussed, none has been adopted to date. To help ensure quality control, the FDA requires that each meter have its own serial number, so problems can be traced. Most makers offer a 24-hour toll-free help line with the phone number on the back of the meter or in the printed material that came with the meter. 5 Two different studies recently published in the veterinary literature evaluated the use of a number of commercially available PBGM for measuring blood glucose concentration in dogs with hyper-, hypo-, and euglycemia compared with measurements obtained by automated analysis of heparinized blood samples using a hexokinase or glucose oxidase reference method, t,3 One of these studies also evaluated the use of a POC

Clinical Techniques in Small Animal Practice, Vol 17, No 2 (May), 2002: pp 70-72

TABLE la. Portable Blood Glucose Meters Commonly Used in Veterinary Medicine LXN Duet Blood glucose and fructosamine monitor Rating Ease of Use Precision Accuracy Cost Good for pets Blood (/~1) Test Strips Pros Cons Maker % incorrect decision

Exactec RSG

One Touch Ultra

Medisense Precision

Accu-chek Simplicity

3 Easy Consistent _+ 20% $80 Yes 10 (ct 50) $37 BG (ct 6) $25 Fruct Combination meter

1 More complicated Inconsistent _+ 20% N/A N/A 3

4 Easy Consistent _+ 20% $65 Yes 1 N/A

1 Dtfftcult Inconsistent > 20% N/A N/A 5 N/A

4 N/A Very consistent _+ 20% N/A N/A 4 Comfort Curve, (100 ct), $63

Cost of stnps for fructosamine LXN Not known

Complicated, high rate of errors Exactech 67%

Medisense Not known

Roche Not known

Rated in top 3 in consumer reports Lifescan Not known

TABLE lb. Portable Blood Glucose Meters Commonly Used in Veterinary Medicine

Rating Ease Precision Accuracy Cost Good for pets Blood (/xl) Test Strips Pros

Cons Maker Contact % altered decisions

Glucometer DEX

Glucometer Encore

Glucometer Elite XL

3 Easy Less consistent _+ 20% $68 Yes 3-4 Dex sensors, (ct 50) $40 (ct 100) $70 Convenient for frequent testers Meter can be hand held in any orientation

1 Easy Inconststent _+ 20% $45 Yes 3 Encore (ct 50), $37 Inexpensive

4 Easy Consistent _+ 20% $40, XL $53 Yes 2 Elite(ct 50), $37 Touchable strips Meter can be held in any orientation

No longer available Bayer 800 348-8100 8%*

False reading with too little blood Bayer 800 348-8100 15%*

Consumer reports-good False readings with too little blood Bayer 800 348-8100 Not known

TABLE lc. Portable Blood Glucose Meters Commonly Used in Veterinary Medicine Accu-chek Simphctty

Accu-chek Compact

Accu-chek Advantage

Accu-chek Complete

Accu-chek A

Rating Ease of Use Precision Accuracy Cost Good for pets Time (sec) Blood (/xl) Test Strips

3 Easy Very consistent _+ 20% $65 Yes

3 Easy Conststent _+ 20% $45 Yes

4 Accu-chek compact, (ct 50) $40

3 Accu-chek compact, (ct 50) $40

3 Easy Consistent ÷ 20% $70 Yes 15 3 Accu-chek complete, (ct 50) $40

3 Easy Conststent _+ 20% $45 Yes 5 3 Accu-chek acti (ct 50) $40

Pros

Touchable strips

Touchable strips

4 Easy Consistent _+ 20% $60 Yes Up to 40 3 Comfort Curve, (100 ct), $63 Accu-chek advantage, (ct 50) $40 Touchable strips

Touchable strips

Can be held in any orientation Second drop w/in 15 sec

Can be held in any orientation Second drop w/in 15 sec

5 second readTouchable stnp Can be held in orientatton Second drop w/sec

Cons Maker Contact

800 858-8072

Roche 800 858-8072

Can be held In any orientation Second drop w/in 15 sec Very accurate Rated in top 3 False reading wtth too little blood Roche 800 858-8072

Can be held in any orientation Second drop w/in 15 sec Roche 800 858-8072

Roche 800 858-8072

*Data from Cohn LA, et al, J Amer Vet Med Assoc, 2000: 216(2): 98-202. Product information provided by manufacturers.

analyzer and color test strips. The PGBM evaluated m these studies included the Glucometer Elite (Elite), the Glucometer DEX (DEX), the SureStep, the Precision QID (QID), the AccuChek Simplicity (Accu-Chek), the Glucometer Glucofilm (Glucofilm), the Glucometer Encore (Encore), the Accu-Chek Easy (Accu-Chek), the ExacTech RSG (ExacTech), and the Glucometer Elite (Elite). The results of these two studies differed, however, with one study concluding that PBGM provided a sufficiently accurate measurement of the animals' blood gluPORTABLE BLOOD GLUCOSE METERS

cose to warrant thei r use in clinical practice 3, and the other finding significant differences compared with reference measurements that could potentially lead to erroneous clinical decisions being made.1 Additional findings of one study included no significant difference in blood glucose measurements when using a PBGM betwelen fresh blood samples and those anticoagulated with lithium heparin. Table 1 summarizes the results of these studies, i One of the more cdmmon uses of PBGM includes monitoring 71

Ideal Blood Glucose Curve

300 200 ose differe 100

Nadir

Glucose

mg/dl

I

6hrs

Hours Fig 1. Ideal blood glucose curve.

the effectiveness of insulin therapy in the management of diabetic animals through the creation of a blood glucose curve. 6-9 A blood glucose curve is produced by taking an initial blood sample and having the owner feed the same amount and type of food as he or she normally would. Ideally, the chent should administer insulin; this allows assessment of the injection technique. Blood samples are then collected at 2-hour intervals, for 12 hours in most cases. The ideal blood glucose curve ts characterized by three features (Fig 1), including an appropriate glucose nadir, duration, and glucose differential. The ideal glucose curve has a glucose nadir (lowest blood glucose concentration on the curve) between 100 and 150 mg/dL in cats and 80 to 120 mg/dL in dogs. r The time of the glucose nadir indicates peak insulin action. The nadir should occur approximately halfway through the dosing interval. For example, if insulin is being given every 12 hours, the nadir should fall 5 to 6 hours after the dose. The glucose differential is the difference between the glucose nadir and the blood glucose concentration before the next insulin dose. The glucose differential should less than 150 mg/dL in cats. 9 The ideal glucose curve in a cat receiving twice-per-day insulin injections starts at 250 mg/dL, with a nadir of 100 mg/dL and a return to 250 mg/dL 12 hours later. The ideal glucose curve in a dog starts at 200 mg/dL, a nadir of 80 mg/dL, and a return to 200 mg/dL 12 hours later. The duration of insulin action is related to the both the time of the glucose nadir and the absolute concentration of the glucose nadir. One cannot make a determination of insulin duration unless the target glucose nadir concentration (80-150 mg/dL) has been achieved. If the glucose nadir occurs approximately halfway through the dosing interval, the duration of action of insulin should be adequate. It is rare to obtain a perfect glucose curve in a single animal or even a repeatable curve in the same animal over time. Gener-

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ally, blood glucose curve problems can be differentiated by the characteristics of the curve and the insulin dosage (per dosing interval). If the animal is receiving > 2.2 U/kg of insulin per dose, insulin resistance should be investigated. Causes of insulin resistance in cats include hyperthyroidism, hyperadrenocorticism, acromegaly, estrus, drug therapy~ and concurrent infections (especially urinary). If the animal is receiving < 2.2 U/kg per dose, the blood glucose curve will usually be indicative of one of the following: insufficient dosage of insulin, short duration of action of insulin, insulin-induced hypoglycemic hyperglycemia (Somogyi effect), insulin overlap or prolonged insulin action. Corrective actions include, respectively, increasing the insulin dose, changing to a longer acting insulin or twice-daily insulin regimen, reducing the insulin dose by 25%, or changing to a shorter duration or mixture of insulin (e.g., 30% regular, 70% NPH). In summary, the use of PBGM has become increasingly popular and useful in veterinary medicine, particularly in the management of animals with diabetes mellitus. However, as with all diagnostic tests, the clinician must be aware of the potential limitations of the device, and interpret the results in light of all information available. Additional information such as that provided by serum fructosamlne measurements may prove invaluable in the successful management of diabetic dogs and cats. When critical decisions regarding animal management must be made, particularly with regard to hypoglycemia, clinical judgment and experience is every bit as important as the results of a measured blood glucose concentration. References 1. Cohn LA, McCaw DL, Tate DJ, et al: Assessment of five portable blood glucose meters, a point-of-care analyzer, and color test strips for measuring blood glucose concentration in dogs. JAVMA 216:198202, 2000 2. Saman A0 Ftschbacher CH, Jagemann KU, et al: Non-invastve blood glucose monitoring by means of near infrared spectroscopy: investigation of long-term accuracy and stability. Exp Clin Endocrinol Diabetes 108:406-413, 2000 3. Wess G, Reusch C: Evaluation of five portable blood glucose meters for use m dogs. JAVMA 216:203-209, 2000 4. Geffken G, Winter WE: Hardware and software in diabetes mellitus: performance charactenstics of hand-held glucose testing devices and the application of glycemic testing to patients' daily diabetes management. Clin Chem 47:11-12, 2001 5. Pets with Diabetes: Understanding Home Blood Glucose Meters: www.petdiabetes.org/index.htm 6. Crenshaw KL: Monitoring treatment of diabetes melhtus in dogs and cats. In Current Veterinary Therapy Xlll. Philadelphia, PA, Saunders, 2000 7. Fleeman LM, Rand JS: Management of canine diabetes. In The Veterinary Clinics of North America, Philadelphia, PA, Saunders, 2000 8. Greco DS: Diagnosis of diabetes mellitus in cats and dogs. In The Veterinary Clinics of North America, Philadelphta, PA, Saunders, 2000 9. Rand JS, Martin GJ: Management of feline diabetes mellitus. In The Veterinary Clinics of North America, Philadelphia, PA, Saunders, 2000

STEIN AND GRECO