2.1 Laboratory tests for chlamydia trachomatis

The diagnostic tests that are currently available include cell culture, antigen detection and DNA amplification tests. ^24,25,26

There is clear evidence that a modern molecular approach to amplifying deoxyribonucleic acid (DNA), such as ligase chain reaction (LCR) or polymerase chain reaction (PCR), provides a sensitivity approaching 100% and that this is superior to the 60-80% achievable by either cell culture or antigen detection.^{24,25,26,27,28,29,30,31,32} Evidence level IIa

In addition, LCR and PCR can be performed on urine samples, eliminating the need for invasive sampling and simplifying the procedures for obtaining samples.³¹ Evidence level IIa

The role of newer tests such as transcription-mediated amplification (TMA) and strand-displacement amplification (SDA) needs to be clarified.^33,34,35

Given the exquisite sensitivity of molecular methods, independent confirmation of positive results by another method is difficult. Medico-legal cases should continue to be investigated by cell culture, as this remains the only test validated in a court of law.³

The recommended laboratory test for Chlamydia trachomatis is a nucleic acid amplification test (e.g. LCR or PCR).

2.2 Obtaining specimens

Specimens from a variety of sites are suitable for testing. In women a cervical swab, first void urine (i.e. the first part of the stream) and vaginal swab are equally sensitive, although each may miss a small number of positives. Self-taken vaginal swabs are also acceptable specimens for diagnostic purposes. ^24,36,37 Evidence level IIb

The test chosen will depend on the clinical situation. For example, if a vaginal examination is being carried out it is likely that a cervical swab will be submitted. If no examination is planned, then a specimen of urine may be preferred.^31,38 Evidence level IIb

In women who are undergoing a vaginal examination, the specimen should be an endocervical swab.

In women not undergoing a vaginal examination, a first void urine (i.e. the first part of the stream) should be obtained.

A self-taken vaginal swab is an alternative specimen for women who cannot void urine at the time of the visit.

In men, urethral swabs and first void urine have equal sensitivity, but urethral sampling causes discomfort. ^31,38 Evidence level IIa

In men, a first void urine is the sample of choice.