
STI tests may test for a single infection, or consist of a number of individual tests for any of a wide range of STIs, including tests for syphilis, trichomonas, gonorrhea, chlamydia, herpes, hepatitis and HIV tests. No procedure tests for all infectious agents.
STI tests may be used for a number of reasons:
as a diagnostic test to determine the cause of symptoms or illness
as a screening test to detect asymptomatic or presymptomatic infections
as a check that prospective sexual partners are free of disease before they engage in sex without safer sex precautions (for example, in fluid bonding, or for procreation).
as a check prior to or during pregnancy, to prevent harm to the baby
as a check after birth, to check that the baby has not caught an STI from the mother
to prevent the use of infected donated blood or organs
as part of the process of contact tracing from a known infected individual
as part of mass epidemiological surveillance
Not all STIs are symptomatic, and symptoms may not appear immediately after infection. In some instances a disease can be carried with no symptoms, which leaves a greater risk of passing the disease on to others. Depending on the disease, some untreated STIs can lead to infertility, chronic pain or even death. Early identification and treatment results in less chance to spread disease, and for some conditions may improve the outcomes of treatment.
There is often a window period after initial infection during which an STI test will be negative. During this period the infection may be transmissible. The duration of this period varies depending on the infection and the test.
Source: New Medical
Courtesy: Healthprior21

