Measurement of Capillary Blood Glucose Concentrations by Pet Owners: A New Tool in the Management of Diabetes Mellitus
Recently a new method for capillary blood sampling from the ears of dogs and cats was described, which allows the measurement of glucose concentration by means of portable glucose meters. The authors of this report evaluated the suitability of this method for use by pet owners and the potential technical problems. The owners of seven healthy dogs and seven healthy cats were asked to perform two glucose curves (measuring blood glucose concentration every 2 hours for a total of 12 hours). All dog owners and three cat owners were able to perform a reliable blood glucose curve. The most frequently encountered problems were inadequate formation of a blood drop due to excessive digital pressure on the pinna, repeatedly depressing the plunger of the lancet device instead of allowing the negative pressure to slowly build up, and failure to fill the test strip up to the mark. The authors conclude that these steps of the procedure need to be stressed during technique demonstration and that home monitoring of blood glucose concentrations may serve as a new tool in the management of diabetic dogs and cats.
Introduction
Determination of blood glucose concentrations and serial blood glucose curves are important aspects of long-term management of diabetic dogs and cats. These measurements are used to assess insulin efficacy, the glucose nadir, and the duration of effect of insulin, thereby serving as a basis for modifications in insulin therapy.1–4
Historically, blood collection for determination of glucose concentration has been performed predominantly by a veterinarian, because owners are not skilled at venipuncture. However, this is time consuming and expensive for the owner and may affect the blood glucose concentration, as the pet may be stressed in an unfamiliar environment and be reluctant to eat.56
In contrast, many human diabetics perform home monitoring of blood glucose concentrations using a portable blood glucose meter (PBGM) and capillary blood, which is collected by pricking a fingertip with a lancet device.78 It has been determined that home monitoring of blood glucose concentrations by human diabetics results in optimization of metabolic control.9 However, it has also been shown that problems related to blood collection and incorrect use of the PBGM do occur with home monitoring. This can result in erroneous blood glucose measurements, undue changes in treatment, and loss of motivation of the patient.10 Thus, basic training followed by periodic reassessment of the technique is of utmost importance.11–17
In a recent study, the authors demonstrated the feasibility of the collection of capillary blood from dogs and cats using a lancet device designed for humans.18 In all animals, enough blood from the inner aspect of the ear was collected by the same veterinarian for determination of blood glucose concentration using a PBGM. In addition, it was shown that there was good agreement between the glucose concentration of capillary blood and that of venous blood.18 The results of this study suggested that this technique may be suitable for use at home by owners of diabetic companion animals.
The goals of the present study were to evaluate whether pet owners are able to collect capillary blood and perform glucose measurements at home, and to investigate what types of technical problems may arise during these procedures.
Materials and Methods
Animals
The animals used were client owned and consisted of seven healthy dogs and seven healthy cats. The dogs ranged in age from 2 to 10 years (median, 5 years) and were comprised of five spayed females and two intact males. The cats ranged in age from 6 months to 10 years (median, 2 years) and were comprised of three spayed females, three castrated males, and one intact male. Animals were chosen for inclusion into the study when owners were unfamiliar with any kind of blood collection but were willing to learn capillary blood sampling. The study was approved by the veterinary authorities of the Canton of Zurich.
Study Design
In all animals, the results of clinical, hematological, and serum biochemical evaluations were within reference ranges. The methods for collection of capillary blood from the ear using a lancet device and measurement of blood glucose concentration using a PBGM were both explained and demonstrated to the pet owners individually. The owners then performed one or two blood collections with the clinician present. The entire instruction lasted about 30 minutes. The owners were then given a lancet device,a a PBGM,b two forms for recording blood glucose concentrations, and two questionnaires assessing owner experience with the technique. They were asked to perform two blood glucose curves by determining the blood glucose concentration every 2 hours for a total of 12 hours (i.e., consisting of seven blood collections). The second blood glucose curve was performed 1 to 2 weeks after the first. The days on which the first and second blood glucose curves were determined were designated as days 1 and 2, respectively. The blood glucose measurements were recorded, and the questionnaire was filled in after each blood glucose curve. Those owners who were not able to collect blood at home received a second instruction in the clinic.
Blood Collection and Blood Glucose Concentration Measurement Technique
This technique has been previously described19 and is shown in Figure 1. Briefly, the tip of the ear was held between the thumb and index finger (it was left to the discretion of the owner as to which ear pinna to use), and the entire surface of the outer pinna was held flat using the remaining fingers of the same hand. With the other hand, the lancet device was lightly placed on a nonhaired area of the pinna so that an airtight seal was formed between the endcap of the device and the skin. When the plunger cap of the instrument was pressed, a lancet moved quickly back and forth once. Pressure between the endcap and the skin was maintained while the plunger was slowly released. The skin of the ear began to slightly bulge up into the endcap, because of the developing negative pressure. The formation of a drop of blood was hastened by releasing the pressure that was exerted on the surface of the pinna by those fingers holding the pinna in a flat position. When an adequate amount of blood appeared on the skin, which was visible through the transparent endcap, the plunger was pressed down to release the negative pressure, and the lancet device was removed. Then the test strip in the PBGM was brought into contact with the blood drop, and the required amount of blood was automatically drawn onto the test strip. The concentration of blood glucose was shown on the PBGM display 29 seconds later. The owners were instructed to warm the ear by rubbing it or to change the lancet in the lancet device when an insufficient amount of blood was obtained. Usually the same lancet was used to perform a blood glucose curve (i.e., for seven blood glucose measurements); the lancet was cleaned in between when needed.
The PBGM was calibrated before it was given to the owner, and further calibration during the study was deemed unnecessary. The owners were shown how to perform a control measurement with a control test strip and were encouraged to do this prior to the blood glucose curve on each day.
Questionnaire
There were a total of 18 questions divided into seven sections that related to the following aspects of blood collection and glucose measurements: restraint of the animal, generation of a vacuum with the lancet device, generation of a drop of blood, absorption of blood onto the PBGM test strip, overall use of the equipment, patient tolerance of the procedure, and judgment regarding its feasibility.
Statistical Analysis
All results were analyzed by means of parameter-free statistical methods.c Ranges and median values are given. The Mann-Whitney-U-Test was used to determine differences. Differences were considered significant at P<0.05.
Results
Dogs
Four of the seven owners completed both blood glucose curves without additional instruction. One of these four owners reported having no problems during the entire study. The problems encountered most frequently by the other three owners were generation of negative pressure with the lancet device (n=2), generation of a drop of blood (n=2), and handling of the PBGM (n=1). However, after repeated attempts they were able to overcome these difficulties on their own. The remaining three owners were unable to obtain a blood glucose measurement on the first day because of technical problems, which included inability to generate negative pressure with the lancet device (n=1) and inadequate absorption of the blood drop (n=2). The problem with the generation of negative pressure was due to incorrect use of the lancet device. Instead of allowing the negative pressure to slowly build after depressing and releasing the plunger once, this owner had repeatedly depressed the plunger. Additionally, the negative pressure was inadequate because the owner failed to reduce the pressure exerted by the fingers on the surface of the pinna. The problem with the absorption of the blood drop was due to the erroneous attempt to drop the blood onto the test strip rather than allowing the blood to be absorbed automatically by the strip. This resulted in an inadequate amount of blood for correct measurement by the PBGM. Additional technical problems that were experienced by those owners who were unable to obtain a measurement on day 1 were failure to produce an adequate amount of blood (n=1) and inadequate restraint of the dog (n=1). The problems were identified during a second consult. After the technique was explained and demonstrated a second time, these three owners were able to perform the second blood glucose curve without difficulty.
With respect to the whole group, patient resistance to the blood collection technique was shown on day 1 during generation of a negative pressure (n=4), lancing of the skin (n=3), and restraint (n=1). On day 2, less negative reactions were recorded; they appeared during generation of a negative pressure (n=3) and lancing of the skin (n=1). Generally, the dogs tolerated the procedure well. On day 1, a second person was required to restrain three of the dogs, whereas the other four owners were able to collect blood and operate the PBGM alone. Two of the latter reported having minor problems with the restraint of their dogs. On day 2, a second person was required to restrain one dog only. The incidences of technical problems encountered in dogs are reported in Table 1.
Operation of the PBGM generally was not a problem for owners. Four had difficulty coordinating the positioning of the ear and placing the test strip in the PBGM to allow absorption of the blood onto the test strip. The control measurements were performed without difficulty by all of the owners prior to the blood glucose curve on each day; the results were always within the reference range. Overall procedure assessment is provided in Table 2.
Cats
Two of the seven owners were able to perform both blood glucose curves without additional instruction. One other owner was unable to perform the first blood glucose curve. The problem was due to insufficient generation of negative pressure because of incorrect use of the lancet device (repeated depression of plunger as in the above-mentioned dog). However, after the procedure was explained and demonstrated a second time and the help of a second person was obtained to restrain the cat, this owner completed the second blood glucose curve.
The procedure could not be performed by the remaining four owners. Two of the four cats resisted restraint throughout the entire study, and blood could not be collected for any blood glucose determination. This was attributed to poor tolerance of the procedure, even with a second person’s help in restraining the animal. The other two of the four cats tolerated collection of blood only sporadically, so a complete blood glucose curve was not possible. In one of those two cases, bilateral aural hematomas developed, which made the generation of a blood drop impossible. The second cat became fractious after several unsuccessful attempts to collect blood and subsequently did not tolerate the procedure. Additional problems encountered by these two cat owners included inability to generate negative pressure using the lancet device (n=1) and inability to obtain an adequate amount of blood (n=1).
Repeated instruction and demonstration of the procedure did not aid the four cat owners who were unsuccessful in performing a blood glucose curve.
With respect to the whole group, patient resistance to the blood collection technique appeared during restraint (n=4), lancing of the skin (n=4), and generation of a negative pressure (n=2) on day 1. On day 2, there was no improvement in the demeanor of the cats during the procedure. Operation of the PBGM and test strips generated few problems for the cat owners. As well, the control measurements were performed once daily without difficulty; all measurements were within the required range. Overall procedure evaluation in the cats studied and incidence of technical problems are provided in Tables 2 and 3, respectively.
Glucose Measurements
A total of 77 blood glucose measurements were done in dogs, and 35 were done in cats. In four instances (four different animals: two dogs and two cats), the PBGM registered “lo” (low, <1.1 mmol/L), which was attributed to an insufficient amount of blood. In the dogs studied, the blood glucose concentrations obtained during glucose curves ranged between 1.9 and 5.4 mmol/L (median, 3.7 mmol/L). Three (3/77, 4%) glucose measurements were <2.8 mmol/L (1.9 mmol/L [n=2], 2.2 mmol/L [n=1]).
In the cats of this study, the blood glucose concentrations obtained during glucose curves ranged between 1.8 and 4.1 mmol/L (median, 3.3 mmol/L). Three (9%) measurements were <2.8 mmol/L (1.8 mmol/L, 2.6 mmol/L, 2.7 mmol/L). Glucose concentrations were evaluated statistically in those six animals (four dogs and two cats) in which both glucose curves were obtained. There was no statistically significant difference between days 1 and 2.
Discussion
The concept of home monitoring of blood glucose concentration in dogs and cats stemmed from the experience in human medicine where it has gained wide acceptance in the management of diabetic individuals. The collection of capillary blood from the ear of diabetic dogs and cats and the measurement of blood glucose concentration with a PBGM are performed routinely in the authors’ clinic to determine blood glucose curves. Previous studies have shown that there is good correlation between the glucose concentrations of capillary and venous blood.18 For the majority of veterinarians and veterinary students, the procedure is easy and quick to perform. An adequate amount of blood can be obtained relatively easily with the lancet device used because of the negative pressure created by the device.18 The results of this study indicate that this is also true for dog owners and some cat owners.
Recent studies have evaluated a variety of different PBGMs.19–21 The results obtained by them are reasonably close to those obtained with reference methods, although some devices are more accurate than others.19–21 For this study, the authors decided to use the Glucometer Elite PBGM for several reasons. First, it has been shown in the authors’ previous studies that blood glucose values obtained by this PBGM are reasonably close to reference methodology.2021 Second, in contrast to other PBGMs, which may over- and underestimate the glucose concentrations, the Glucometer Elite almost always slightly underestimates them. Therefore, deviations from the reference values are more calculable than those of other PBGMs.2021 Third, in the authors’ experience, the Glucometer Elite is the easiest PBGM to use, as it has no buttons to press, it turns on automatically when the test strip is inserted, and it requires only a small amount of blood.182021
To the authors’ knowledge, there are no studies that have investigated the use of home monitoring of blood glucose concentrations of dogs and cats by their owners and the associated potential problems. When instructing the owners, it is important to stress that an adequate amount of blood is needed for the PBGM to measure the glucose concentration correctly. The authors theorize that this was the explanation for those cases in which the PBGM registered “lo.” Additionally, blood glucose levels were unexpectedly low (<2.8 mmol/L) in six instances. Previous studies have revealed that a weak point in the measuring procedure using the Glucometer Elite is that an insufficient amount of blood may result in inaccurate, low readings without giving an error message.1920 Therefore, the authors are unable to tell if those readings of <2.8 mmol/L were due to a handling error or due to truly low blood glucose concentrations. Recently, the new generation of Glucometer Elite has been marketed; this PBGM requires even less blood; therefore, it seems that this potential problem can be minimized in the future.
In this study, there was a clear difference between the results of dogs and cats. Most of the dog owners reported that their pet tolerated blood collection well. All of the dog owners reported that their technique for blood collection and use of the PBGM improved quickly and that this led to an increased confidence in the results. In contrast, only three of seven cat owners were able to perform one or both blood glucose curves. These owners also reported that the procedure became easier to perform after they had gained some experience. The owners also found that the cats were more tolerant of blood collection when they were placed in a favorite spot, such as a windowsill or bed. Interestingly, the two cats that readily tolerated the procedure were the only indoor cats of the group. In four of the seven cats, no blood curve was obtained. For these four cat owners, further technical support from their veterinarian did not help, because the errors were not of a procedural nature. The problems that were encountered in three of the four cats were attributed entirely to their disposition. In the fourth case, bilateral aural hematomas developed, which were probably attributable to the delicate ear structure of this breed (i.e., Devon rex). Similar lesions did not occur in any of the other cats or dogs. In fact, the sites of blood collection were barely visible and not painful. In contrast to the dogs, the cats did not become accustomed to the procedure. With one exception, the collection of blood from cats was either well tolerated from the start or not tolerated at all.
It is important that owners of diabetic dogs or cats doing home monitoring have ready access to veterinary support, if required. Ten of 14 owners called for advice one or more times, particularly on day 1. Some had specific questions regarding the procedure, while others wanted reassurance that they were performing the procedure correctly. After day 1, two dog owners were discouraged to the point that they did not want to continue. However, after deliberate discussion, they went on to complete the blood glucose curves without further problems. When support via telephone did not suffice, owners were given additional detailed explanations and demonstrations at home or in the clinic. The latter was ideal for immediate identification and correction of errors. At the end of the study, all of the dog owners said that they would perform this procedure on a regular basis if they had a diabetic animal. Three owners commented that without the extra motivation and support, which allowed them to successfully complete the second blood glucose curve, they would have decided differently. As expected, only three of the cat owners said they would perform this procedure on a regular basis; these were those owners who were able to complete one or both blood glucose curves.
The prerequisite for good owner instruction is that the veterinarian himself is able to perform the procedure correctly and that he is aware of all potential sources of errors. According to the authors’ results, the most frequently encountered problems were inadequate formation of a blood drop due to excessive pressure with the finger on the pinna during use of the lancet device, repeatedly depressing the plunger of the lancet device instead of allowing the negative pressure to slowly build up, and failure to fill the blood glucose test strip up to the mark. These steps of the procedure need to be stressed and better clarified during both the explanation and demonstration of this technique. Frequent reassessment of the technique will also increase both owner and veterinarian confidence in the results generated.
Home monitoring of blood glucose concentration in human diabetics has been performed for many years and has become the foundation to proper treatment of diabetics.22 The American Diabetes Association recommends home monitoring of blood glucose concentrations as an essential part of the management of diabetes mellitus.1415 However, it has long been known that many errors can occur during home monitoring of blood glucose concentrations in humans. The National Steering Committee for Quality Assurance in Capillary Blood Glucose Monitoring12 emphasized the importance of patient education with repeated demonstration of the procedures and observation of the patients as they perform them. They recommended reassessment of the technique 30 and 180 days after training and yearly thereafter, or sooner when results indicate possible procedural error. These recommendations should be implemented if home monitoring of blood glucose concentrations is to be successful in diabetic dogs and cats.
The results of this study identified important causes of error in collection of capillary blood from the ear and in the use of the PBGM. The authors have been able to use these results for better education of owners who want to perform home monitoring of blood glucose concentrations in diabetic dogs and cats. Further studies are in progress to determine whether home monitoring of blood glucose concentrations improves the glycemic control of diabetic dogs and cats.
Microlet Vaculance; Bayer Diagnostics, Zurich, Switzerland
Glucometer Elite; Bayer Diagnostics, Zurich, Switzerland
SPSS/PC V 6.0, Base manual; SPSS Inc., Chicago, IL 1993
Citation: Journal of the American Animal Hospital Association 38, 3; 10.5326/0380239
Blood collection technique. (1A) The tip of the ear is held between the thumb and index finger, and the surface of the pinna is held flat by the rest of the fingers. Then the lancet device is set on a nonhaired area of the ear. (1B) An airtight seal between the device and ear is obtained by pushing the outer ear against the device with the tip of one finger. (1C) The lancet is activated by pressing the plunger cap of the device. With slow release of the plunger cap, a negative pressure is created, and the skin slightly bulges up into the endcap. The negative pressure is maintained until there is an adequate amount of blood. (1D) The portable blood glucose meter (PBGM), with the test strip inserted, is placed over the drop of blood. The blood is automatically absorbed, and after 29 seconds the blood glucose concentration is displayed.
Contributor Notes
