title: Effects of diagnostic test accuracy and treatment efficacy on the occurrence of suspected failure of heartworm prophylaxis in dogs.
abstract: BACKGROUND
  Food and Drug Administration Center for Veterinary Medicine (FDA/CVM) cited concern regarding failure of heartworm prophylaxis. The positive and negative predictive value of the heartworm antigen test is an estimate of the probability of adult heartworm infection.
  
  
  OBJECTIVE
  Assess the sensitivity, specificity, and predictive value of heartworm antigen tests. Explore the role of heartworm test accuracy and treatment with immiticide to generate reports of suspected failure of heartworm prophylaxis.
  
  
  METHODS
  Literature searches for published information on the accuracy of heartworm antigen tests and efficacy of immiticide for treatment of the adult heartworm.
  
  
  RESULTS
  Weighted averages for heartworm antigen test sensitivity and specificity were 78.2 and 97.3%, respectively. Efficacy of immiticide by 2-injection or alternate dose protocols were 88.3 and 89.1%, respectively. Depending on prevalence, the positive predictive value of the heartworm antigen test ranged from 15 to 54% and negative predictive value from 99 to 99.9%. For a hospital testing 1,000 dogs per year, false-positive test results may vary from 24 to 27 dogs. If these dogs were on heartworm preventive, they may undergo treatment and be classified as prophylaxis failures. Ten percent of dogs who were treated and continued or placed on prophylaxis at the time of treatment may have adult heartworms when tested 1 year later and be presumed to represent failure of prophylaxis.
  
  
  CONCLUSIONS
  When interpreting heartworm antigen test results, clinical signs, history, and regional prevalence of heartworm disease should be considered in estimating the predictive value of the test result. Limitations of test and treatment should be discussed with clients as part of the decision-making process.
authors.affiliation: Department of Biomedical and Diagnostic Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996-4543, USA. brohrbac@utk.edu
authors.forename: B W
authors.initials: BW
authors.lastname: Rohrbach
authors.forename: S
authors.initials: S
authors.lastname: Patton
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000008:administration & dosage / Q000627:therapeutic use*; D000947:Antigens, Helminth / Q000097:blood*; D004184:Dirofilariasis / Q000517:prevention & control*; D004283:Dog Diseases / Q000517:prevention & control*; D004285:Dogs; D005189:False Positive Reactions; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D017211:Treatment Failure
chemical_list: D000871:Anthelmintics; D000947:Antigens, Helminth
keywords: Canine; Dirofilaria immitis; Immiticide; Predictive value