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Effect of dilution of canine blood samples on the specificity of saline agglutination tests for immune-mediated hemolysis.

ABSTRACT: Background: Saline agglutination tests (SATs) are widely recommended for diagnosis of immune-mediated hemolytic anemia in dogs, but there are frequent false-positive results.

Objectives: Specificity of SATs will improve at higher saline-to-blood ratios.

Animals: One hundred fifty dogs treated at a veterinary referral hospital with hematocrits ?30%.

Methods: Prospective diagnostic accuracy study. Immune-mediated hemolysis (IMH) was considered present if a gel direct antiglobulin test (DAT) was positive and there was clinical evidence of hemolysis (n = 9), absent if another mechanism for anemia was identified and the DAT was negative or there was no hemolysis (n = 138), and if IMH status was unclear, dogs were excluded (n = 3). Saline agglutination tests were prepared at 1 : 1, 4 : 1, 9 : 1, and 49 : 1 saline-to-blood ratios, and microscopic agglutination was considered a positive result.

Results: Specificity for IMH increased from 29% (95% confidence interval 20-38) at a 1 : 1 dilution to 97% (93-99) at a 49 : 1 dilution. Sensitivity was 88% (47-100) at 1 : 1 and 4 : 1 dilutions and 67% (30-93%) at 9 : 1 and 49 : 1 dilutions. Diagnostic accuracy increased from 33% (24-42) at 1 : 1 dilution to 95% (90-98) at 49 : 1 dilution.

Conclusions and clinical importance: If performed using a 49 : 1 saline-to-blood ratio, SATs achieve high specificity for IMH. Based on a gold standard of positive DAT and evidence of hemolysis, lower saline-to-blood ratio results should not be used because false-positive results are common.

SUBMITTER: Sun PL

PROVIDER: S-EPMC7694812 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature

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Effect of dilution of canine blood samples on the specificity of saline agglutination tests for immune-mediated hemolysis.

Sun Prudence L PL Jeffery Unity U

Journal of veterinary internal medicine 20201110 6

<h4>Background</h4>Saline agglutination tests (SATs) are widely recommended for diagnosis of immune-mediated hemolytic anemia in dogs, but there are frequent false-positive results.<h4>Objectives</h4>Specificity of SATs will improve at higher saline-to-blood ratios.<h4>Animals</h4>One hundred fifty dogs treated at a veterinary referral hospital with hematocrits ≤30%.<h4>Methods</h4>Prospective diagnostic accuracy study. Immune-mediated hemolysis (IMH) was considered present if a gel direct antig ...[more]

PMID: 33169867

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Project description:BackgroundPreanalytic factors such as time and temperature can have significant effects on laboratory test results. For example, ammonium concentration will increase 31% in blood samples stored at room temperature for 30 min before centrifugation. To reduce preanalytic error, blood samples may be placed in precooled tubes and chilled on ice or in ice water baths; however, the effectiveness of these modalities in cooling blood samples has not been formally evaluated. The purpose of this study was to evaluate the effectiveness of various cooling modalities on reducing temperature of EDTA whole blood samples.MethodsPooled samples of canine EDTA whole blood were divided into two aliquots. Saline was added to one aliquot to produce a packed cell volume (PCV) of 40% and to the second aliquot to produce a PCV of 20% (simulated anemia). Thirty samples from each aliquot were warmed to 37.7 °C and cooled in 2 ml allotments under one of three conditions: in ice, in ice after transfer to a precooled tube, or in an ice water bath. Temperature of each sample was recorded at one minute intervals for 15 min.ResultsWithin treatment conditions, sample PCV had no significant effect on cooling. Cooling in ice water was significantly faster than cooling in ice only or transferring the sample to a precooled tube and cooling it on ice. Mean temperature of samples cooled in ice water was significantly lower at 15 min than mean temperatures of those cooled in ice, whether or not the tube was precooled. By 4 min, samples cooled in an ice water bath had reached mean temperatures less than 4 °C (refrigeration temperature), while samples cooled in other conditions remained above 4.0 °C for at least 11 min. For samples with a PCV of 40%, precooling the tube had no significant effect on rate of cooling on ice. For samples with a PCV of 20%, transfer to a precooled tube resulted in a significantly faster rate of cooling than direct placement of the warmed tube onto ice.DiscussionCanine EDTA whole blood samples cool most rapidly and to a greater degree when placed in an ice-water bath rather than in ice. Samples stored on ice water can rapidly drop below normal refrigeration temperatures; this should be taken into consideration when using this cooling modality.

Dataset Information

Effect of dilution of canine blood samples on the specificity of saline agglutination tests for immune-mediated hemolysis.

Publications

Effect of dilution of canine blood samples on the specificity of saline agglutination tests for immune-mediated hemolysis.

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