 Dark ground microscopy of serous fluid from a chancre may be used to make an immediate diagnosis . Hospitals do not always have equipment or experienced staff members , whereas testing must be done within 10 minutes of acquiring the sample . Sensitivity has been reported to be nearly 80 % , thus can only be used to confirm a diagnosis but not rule one out . Two other tests can be carried out on a sample from the chancre : direct fluorescent antibody testing and nucleic acid amplification tests . Direct fluorescent testing uses antibodies tagged with fluorescein , which attach to specific syphilis proteins , while nucleic acid amplification uses techniques , such as the polymerase chain reaction , to detect the presence of specific syphilis genes . These tests are not as time @-@ sensitive , as they do not require living bacteria to make the diagnosis . 
