Sensitivity and specificity of a modified agar gel precipitation test and its application to the diagnosis of enzootic bovine leukosis.

Sensitivity and specificity of a modified agar gel immuno-diffusion (AGID) test for the diagnosis of enzootic bovine leukosis was compared in 609 sera using the standard method, the modified test, and ELISA. The modifications concerned the composition of agar gel (1.8% Bacto-agar Difco), addition of polyethylene glycol (PEG 6000, 4%) and enlarging the diameters of the wells from 6 to 10 mm for sera. The change in well diameters and the addition of PEG 6000 increased the sensitivity of the test by about 60-100%, favourably influenced the proper interpretation of the results, especially with weak positive sera. ELISA proved to be more sensitive either than the modified (by 4.1%) or standard AGID (by 5.25%) tests. The modified AGID test may find wide application in laboratory practice, especially when a more sensitive technique is not available.