Sensitivity and specificity of polymerase chain reaction for the detection of Toxoplasma gondii DNA added to laboratory samples

We studied the sensitivity and specificity of PCR to detect T.gondii DNA by aliquoting various concentration of tachyzoites into laboratory specimens from 60 positive and 10 negative buffy-coat samples. We were able to detect the specific gene from purified DNA samples containing as few as 0.25 parasites per 100,000 human leukocytes. These results had an impressive initial 100% specificity but later it decreased because of false-negative data.