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Clinical evaluation of a benchtop dry chemistry analyzer for measurement of ammonium concentrations in canine plasma samples

Silvia Funes DVM1, Jana Gordon DVM2, Elena Gorman DVM, MS3, and Craig Ruaux BVSc, PhD4
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  • 1 Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331.
  • | 2 Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331.
  • | 3 Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331.
  • | 4 Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331.

Abstract

OBJECTIVE To evaluate the clinical performance of a veterinary benchtop dry chemistry analyzer for measurement of plasma ammonium concentrations in dogs by comparing results with those obtained by a reference standard test method.

DESIGN Prospective evaluation study.

SAMPLE 32 blood samples from 30 dogs (16 with and 14 without suspected hepatobiliary disease).

PROCEDURES Blood samples were collected by jugular venipuncture. A veterinary benchtop dry chemistry analyzer and a reference standard (enzymatic) test method were used to measure ammonium concentrations in plasma collected from heparinized whole blood. Bland-Altman plots were used to assess intermethod agreement. Results were compared by linear regression, and correlation was calculated by the Pearson method. Samples were classified as having high or normal ammonium concentrations on the basis of cutoff data for the relevant test method; results were compared between methods to evaluate diagnostic agreement.

RESULTS 31 of 32 (97%) samples were classified correctly with the benchtop analyzer; 1 sample with a high ammonium concentration was classified as having a normal value (ie, false-negative result) by this method. A strong positive correlation (r2 = 0.989) was found between methods, with constant, proportional, negative bias for benchtop analyzer results. The interassay coefficient of variation (ie, precision) for measurement of an internal standard with the benchtop analyzer was 2.74% (n = 20 repetitions).

CONCLUSIONS AND CLINICAL RELEVANCE The dry chemistry analyzer used in the study had acceptable clinical performance for detection of high versus normal ammonium concentrations in canine plasma, indicating the method can be used to aid diagnosis in dogs with suspected hepatobiliary disease.

Abstract

OBJECTIVE To evaluate the clinical performance of a veterinary benchtop dry chemistry analyzer for measurement of plasma ammonium concentrations in dogs by comparing results with those obtained by a reference standard test method.

DESIGN Prospective evaluation study.

SAMPLE 32 blood samples from 30 dogs (16 with and 14 without suspected hepatobiliary disease).

PROCEDURES Blood samples were collected by jugular venipuncture. A veterinary benchtop dry chemistry analyzer and a reference standard (enzymatic) test method were used to measure ammonium concentrations in plasma collected from heparinized whole blood. Bland-Altman plots were used to assess intermethod agreement. Results were compared by linear regression, and correlation was calculated by the Pearson method. Samples were classified as having high or normal ammonium concentrations on the basis of cutoff data for the relevant test method; results were compared between methods to evaluate diagnostic agreement.

RESULTS 31 of 32 (97%) samples were classified correctly with the benchtop analyzer; 1 sample with a high ammonium concentration was classified as having a normal value (ie, false-negative result) by this method. A strong positive correlation (r2 = 0.989) was found between methods, with constant, proportional, negative bias for benchtop analyzer results. The interassay coefficient of variation (ie, precision) for measurement of an internal standard with the benchtop analyzer was 2.74% (n = 20 repetitions).

CONCLUSIONS AND CLINICAL RELEVANCE The dry chemistry analyzer used in the study had acceptable clinical performance for detection of high versus normal ammonium concentrations in canine plasma, indicating the method can be used to aid diagnosis in dogs with suspected hepatobiliary disease.

Contributor Notes

Dr. Ruaux's present address is Institute of Veterinary, Animal, and Biomedical Sciences, Massey University, Palmerston North 4474, New Zealand. Dr. Funes' present address is VCA Bay Area Veterinary Specialists, 14790 Washington Ave, San Leandro, CA 94578.

Address correspondence to Dr. Funes (silvia.funes@oregonstate.edu).