<i>Dirofilaria immitis</i> antigen detection in the urine of dogs with known and unknown infection status

Canine heartworm, <i>Dirofilaria immitis</i>, causes a potentially fatal, multisystemic disease in dogs. Diagnosis of heartworm disease relies on serologic antigen detection and microfilariae identification. Immune-complex dissociation (ICD) of serum or plasma by heat treatment increases detection. We assessed urine as a sample for heartworm antigen detection in dogs with known and unknown infection status using a commercial ELISA. Twenty-nine matching serum or plasma and urine samples were collected from 20 experimentally infected dogs to assess antigen detection in urine. Matching serum and urine samples of 267 dogs admitted to a spay/neuter clinic with unknown infection status were also screened. In experimentally infected dogs, antigenemia was detected in 86% of samples pre-ICD and 91% post-ICD; antigenuria was detected in 76% pre-ICD and 72% post-ICD; differences were not statistically significant. In clinic samples, antigenemia was detected in 7.9% of dogs pre-ICD and 12.4% post-ICD; antigenuria was detected in 11.6% of dogs pre-ICD and 6.4% post-ICD. In experimental infection samples, sensitivity (Se), specificity (Sp), and positive predictive value of antigenuria were high (85%, 100%, 100%, respectively). In clinic samples, Se and negative predictive value were high (95% and 92%, respectively). Our data confirm that heartworm antigen can be detected in the urine of dogs with both experimental heartworm infections and with unknown infection status. However, antigenuria had high Sp and low Se compared to matching serum of clinic dog samples and urine cannot be recommended for routine screening.