Effect of dilution of canine blood samples on the specificity of saline agglutination tests for immune‐mediated hemolysis. (10th November 2020)

• Record Type: Journal Article
• Authors: Sun, Prudence L.; Jeffery, Unity
• Is Part Of: Journal of veterinary internal medicine. Volume 34:Number 6(2020)
• Page Start: 2374
• Page End: 2383
• Publication Date: 2020-11-10
• Subjects: accuracy -- autoimmune hemolytic anemia -- Coombs test -- diagnosis -- immune‐mediated hemolytic anemia -- sensitivity; Veterinary medicine -- Periodicals; 636.0896
• DOI: 10.1111/jvim.15945
• Languages: English
• ISSNs: 0891-6640

Abstract

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.