Measuring the level of agreement between a veterinary and a human point-of-care glucometer and a laboratory blood analyzer in Hispaniolan Amazon Parrots (Amazona ventralis).
Key words: point-of-care diagnosis, screening, blood glucose meter, glucometer, avian, Hispaniolan Amazon parrot, Amazona ventralis
In small-animal medicine, hyperglycemia and hypoglycemia are commonly encountered hematologic abnormalities and are often associated with endocrine disorders and critical illnesses. Effective monitoring of these patients necessitates point-of-care (POC), serial blood glucose measurements that use minimal amounts of blood. Since their introduction in the late 1970s, inexpensive and accurate handheld POC glucose meters have revolutionized the treatment of blood glucose abnormalities in people (1) as well as in cats and dogs. (2) The routine use of these POC devices has been made possible by studies that have validated their use in relevant species. (3-5)
Abnormalities in blood glucose concentrations are not believed to be as common in avian species as they are in mammals (6); however, the inability to provide POC measurements may lead to underreporting. Moreover, in companion avian species, hyperglycemia secondary to diabetes, stress, and steroids has been documented, (7) whereas hypoglycemia has been reported in cases of starvation, liver disease, aspergillosis, and sepsis. (7,8) The cost and time associated with sending serum samples to central laboratories has limited the use of blood glucose monitoring in critically ill avian patients.
A previous study (8) involving rhinoceros auklets (Cerorhinca monocerata) found that handheld glucometers consistently underestimated blood glucose concentrations, making the devices useful only for screening. A study (9) in psittacine birds found that POC blood glucose devices also underestimated blood glucose concentrations; however, the degree of variability was too great for those devices to be considered useful diagnostic instruments. To our knowledge, no study has validated a POC glucometer for use in psittacine birds, which are commonly kept as companion animals.
Recently, a glucometer (AlphaTRAK, Abbott Laboratories, Abbott Park, IL, USA) specifically designed for veterinary patients was produced. This coulometric electrochemical device uses an animal-specific code in conjunction with a proprietary algorithm to determine blood glucose concentrations. Specific codes have been produced for cats and dogs; however, specific codes have not been developed for birds. The purpose of this study was threefold. The first objective was to obtain data necessary for the manufacturer of the veterinary glucometer to derive a psittacine bird-specific code. The second objective was to determine whether blood glucose measurements for psittacine birds made with the veterinary POC meter were in good agreement with those of a laboratory analyzer. Lastly, we tested a commercially available, previously untested, POC standard glucose meter (Ascensia ELITE, Bayer Healthcare, Pittsburgh, PA, USA) to determine whether its results were in good agreement with those of a laboratory analyzer. Our hypothesis was that the veterinary glucometer would produce values that were in good agreement with a laboratory analyzer, whereas the standard human glucometer would not.
Materials and Methods
Twenty-five clinically healthy, adult Hispaniolan Amazon parrots (Amazona ventralis), which were part of the research flock at the School of Veterinary Medicine, Louisiana State University (Baton Rouge, LA, USA), were used in this study. The only inclusion criterion was enough blood could be collected in a single draw to run all tests for that specific evaluation point in the study. Hispaniolan Amazon parrots were selected because their size, dietary requirements, and physiology are comparable to many other popular psittacine bird species that are often kept as companion animals. This study was performed in accordance with the regulations set forth by the Institutional Animal Care and Use Committee at Louisiana State University.
Twenty birds, which were a subset of the total 25 used in this study, were included in the initial phase of the project. Each bird was examined to ensure that it was in good health. A 26-gauge needle and a 3-mL syringe were used to withdraw approximately 0.5 mL of blood from the right jugular vein of each bird. A small volume of fresh blood (0.3 [micro]L) was used to measure blood glucose concentrations with the veterinary glucometer, and another 50 [micro]L was used to measure packed cell volume (PCV) by the microhematocrit tube method. The remainder of each sample was placed into a lithium heparin microtainer tube (Microtainer, Becton-Dickinson, Franklin Lakes, NJ, USA) and centrifuged. Plasma was harvested and frozen at -30[degrees]C. Within 5 days, the samples were thawed, and the plasma glucose values were determined with a laboratory-based chemistry analyzer (Olympus AU640e, Olympus America Inc, Center Valley, PA, USA). This procedure was repeated 14 days later, and the resulting data sets (glucometer values, laboratory values, and PCV results) were provided to the glucometer manufacturer (Abbott Laboratories). This information was used to develop a psittacine bird-specific glucometer code.
The second phase of the study was done approximately 1 month after collection of the second blood sample. A 26-gauge needle and a 3mL syringe were used to withdraw approximately 0.5 mL of blood from the right jugular vein of 25 birds. A small volume of blood (0.3 [micro]L) was used to measure blood glucose concentrations with the veterinary glucometer and the standard glucometer (2.0 [micro]L) and to measure PCV by the microhematocrit tube method (50 [micro]L). Both meters were calibrated in accordance with the manufacturer's specifications and were operated by an individual specifically trained in their use (R.S.). The rest of each blood sample was placed into a lithium heparin microtainer tube and centrifuged. Plasma was harvested and frozen at -30[degrees]C. Within 5 days, the samples were thawed, and the plasma glucose values were determined with a laboratory-based chemistry analyzer. This procedure was repeated 14 days later.
[FIGURE 1 OMITTED]
Distribution of the laboratory blood glucose concentrations was evaluated by the Kolmogorov-Smirnov test. Agreement between results for each of the POC meters and for the laboratory analyzer was evaluated by the Bland-Altman method. (10) Bias was defined as the mean difference between the 2 methods, and limits of agreement were calculated as the bias [+ or -] 1.96 SD. Standards in human medicine recommend that the accuracy of a POC meter be within 15% of the reference value (11); therefore, the units were considered to be in agreement with the standard if the limits of agreement were within 15% of the laboratory values. Statistical analyses were performed with commercially available statistical software (Prism, version 5.0 for Macintosh, GraphPad Software Inc, San Diego, CA, USA).
All 40 venipunctures in the first phase of the study and 45 of 50 in the second phase were successful. Blood glucose values obtained by the laboratory analyzer were normally distributed with a mean [+ or -] SD of 206.5 [+ or -] 29.5 mg/dL. Agreement was poor between values obtained with the laboratory chemistry analyzer and those from the veterinary glucometer (bias, 9.0; limits of agreement, -38.1 to 56.2; Fig 1), as was agreement between values obtained with the laboratory chemistry analyzer and those from the standard glucometer (bias, 69.4; limits of agreement,-17.8 to 156.7; Fig 2).
[FIGURE 2 OMITTED]
Neither glucometer was in agreement with the results of the laboratory analyzer for blood glucose concentration. The veterinary glucometer's relatively small, positive bias demonstrates that the device underreported blood glucose concentrations by an average 9 mg/dL; however, the majority of individual readings were in a range from less than 56.2 mg/dL or more than 38.1 mg/dL actual blood glucose concentrations. The standard commercially available glucometer had a strong positive bias, suggesting an average underreporting of blood glucose concentrations by 69.4 mg/dL. Most values ranged from less than 156.7 mg/dL to more than 17.8 mg/dL of the actual blood glucose concentrations.
One possible explanation for the difficulty that these units had in determining the correct blood glucose could be that avian species tend to have higher hematocrit values than do their mammalian counterparts. Previous studies have shown that increases in hematocrit levels can cause glucometer inaccuracies. (12) However, the hematocrit values for the birds in this study ranged from 40% to 61%, which was within the specifications for each meter. Another possibility is that the blood glucose concentration of a psittacine bird is too high for handheld glucometers to accurately measure. All the blood glucose concentrations reported in this study were within the published specifications of each meter; however, a study in dogs demonstrated that, as canine blood glucose concentrations increased, agreement between the values of the veterinary glucometer and those of the reference laboratory decreased. (13) A confounding factor may be that the structural differences between mammalian and avian red blood cells (ie, presence of the nucleus) might reduce the current flow needed for accurate electrochemical glucose measurement.
Abnormalities in blood glucose concentrations are commonly diagnosed in companion animals and are seen as both the consequence of endocrine disorders and critical illnesses. The availability of accurate POC glucometers has significantly improved the treatment of these patients by allowing near-instantaneous, serial glucose measurements. The incidence of hyperglycemia and hypoglycemia in birds is thought to be lower than it is in cats and dogs; however, the lack of accurate POC measurements may be an obstacle in identifying affected patients. In addition, laboratory measurements are more expensive and require significantly more blood than that needed for an accurate, handheld glucometer, if it were available.
In this study, we obtained 2 blood samples 2 weeks apart from 20 birds. Laboratory and glucometer blood glucose concentrations, as well as PCVs, were determined and provided to the manufacturer for developing a glucometer code for psittacine birds. Once we obtained this code (7), we drew blood from 25 birds twice, 2 weeks apart, and compared the results from a veterinary glucometer and a standard glucometer with those of a laboratory analyzer. Although the veterinary glucometer produced values that were closer to those of the laboratory analyzer than did the standard glucometer, neither was in agreement with the laboratory analyzer. In addition, no trend was identified that would allow for adjustment of the results. Therefore, use of these glucometers in psittacine birds cannot be recommended at this time.
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Mark J. Acierno, MBA, DVM, Dipl ACVIM, Rodney Schnellbacher, DVM, and Thomas N. Tully Jr, DVM, MS, Dipl ABVP (Avian), Dipl ECZM
From the School of Veterinary Medicine, Louisiana State University, Skip Bertman Dr, Baton Rouge LA 70810, USA. Present address (Schnellbacher): College of Veterinary Medicine, University of Georgia, 501 DW Brooks Dr, Athens, GA 30602, USA.
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|Title Annotation:||Original Studies|
|Author:||Acierno, Mark J.; Schnellbacher, Rodney; Tully, Thomas N., Jr.|
|Publication:||Journal of Avian Medicine and Surgery|
|Date:||Dec 1, 2012|
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