Diagnosis of canine filariosis: relative sensitivity and specificity of some haematological techniques.

Blood samples from 329 dogs of an hyperendemic area in Northern Italy were examined for filariosis. At the filter method (5 microns), taken as reference test, 163 (49.5%) were positive: 160 for Dirofilaria immitis, 2 for D. repens and 1 for both species. The direct smear test (DS), the modified Knott technique (KT) and a further modification of the Knott technique (MKT) were performed in order to assess their relative sensitivity (SE), specificity (SP), positive and negative predictive values (PPV and NPV). The relative SE values are of 88.3%, 91.0% and 91.8% for DS, KT and MKT, respectively. Only the DS relative SP value (99.3%) is less than 100%. Also the PPV and NPV are very high (all above 89%) as well as the values of the coefficient Kappa (all above 0.8), a measure of the concordance between the results of the FT and of the comparison tests.