The past and present role of the Sabin-Feldman dye test in the serodiagnosis of toxoplasmosis

The dye test for the detection of Toxoplasma-specific antibodies was first described by Sabin and Feldman 50 years ago. The test is highly specific an d sensitive and considerable information is available on the development an d persistence of dye test antibodies after primary Toxoplasma infection. Ho wever, the test uses live Toxoplasma gondii and is now only employed in a f ew laboratories. It is still the reference method for the serodiagnosis of toxoplasmosis, and a multicentre study comparing dye test results between d ifferent laboratories was much needed. We report in this article the results of a multicentre evaluation of the te st involving nineteen laboratories in eight countries. The study revealed o verall satisfactory standardization between the laboratories, but there wer e differences in the test protocols, the use of reference/standard preparat ions and the interpretation of results. There is still no agreement on the level of dye test values which reflect infection with the parasite, and con version from titres to international units (IUs) did not improve standardiz ation. However, the results indicated that a value of > 4 IU or a titre of 1:16 met the definition of positivity of most participants. We recommend that the dye test be retained as a reference method and that i nterlaboratory standardization be improved by the use of a common protocol and the expression of results in titres.