Laboratory diagnosis of sexually transmitted infections

The laboratory plays a central role in the accurate diagnosis of sexually transmitted infections (STIs). In countries with sufficient resources the laboratory is usually involved in providing a result to inform individual patient management. In contrast, in resource-poor countries where patients are often treated according to their presenting symptoms (syndromic management), the laboratory has a role in evaluating this approach. Molecular detection of the causative agents of STIs, such as Neisseria gonorrhoeae, Chlamydia trachomatis and herpes simplex virus (HSV), using highly sensitive and specific tests, has largely replaced classical culture techniques. The detection of the host's antibody response to the infecting agent is still the mainstay for the diagnosis of syphilis and human immunodeficiency virus (HIV). In some instances a combination of antigen and antibody detection is used. In the United Kingdom, where a unique network of open-access specialized clinics exists, some laboratory procedures are performed in a clinic laboratory setting and this is particularly useful for common causes of vaginitis that can be diagnosed using a microscope. This article describes the current methods employed for the major causes of bacterial and viral sexually transmitted infections.