Blocked Antigen Causes False-Negative Heartworm Test Results

The American Heartworm Society and Companion Animal Parasite Council recommend 2 components for diagnosing heartworm infection in small animal patients: antigen detection assay and microscopic identification of Dirofilaria immitis microfilaria. The antigen test is generally considered the more sensitive test, but studies estimate that 6.0% to 38.7% of microfilaria-positive samples produce negative antigen test results.