Assays to diagnose infectious disease must be: specific (no false positives or cross reactivity); and sensitive (able to identify even a single cell). Indirect assays detect antibodies, which are evidence of past and perhaps prsent infection. Direct assays detect the parasite itself.
|DNA Assay||Direct||PCR detection of any microbe has two criteria: specificity to detect only the microbe in question; and sensitivity to detect the microbe at low abundance.|
|Microscopy||Direct||Diagnostic microscopy is usually performed on blood smears or following culture in synthetic media. Centrifugation can be performed to concentrate scarce parasites into a white cell layer called the buffycoat.|