Timing of chlamydia tests

Carolyn E Rigg, F2 SHO,
, ,

Other Contributors:

May 20, 2008

Dear Editor,

In the editorial Focus on chlamydia(1), screening of asymptomatic individuals to prevent transmission and adverse consequences of chlamydia was discussed. We wish to raise the issue of uncertainty around the appropriate timing of chlamydia tests in relation to exposure.

The National Chlamydia Screening Programme (NCSP) Core Requirements (3rd Edition) states ‘There is no data on the use of nucleic acid amplification tests (NAATs) and how soon after sex a test may become positive’ and advises to test immediately and repeat the test in 3-5 weeks(2).

A local (i.e. Central Lancashire PCT) NCSP poster states ‘The test should be taken 3 weeks after sexual contact, as the infection may not show immediately’.

The British Association for Sexual Health and HIV (BASHH) UK National STI Screening and Testing Guidelines indicate that the minimum time gap between exposure to a sexually transmitted infection and its successful detection varies depending on a number of factors including the organism, the size of inoculum and the type of test used. These guidelines highlight that the evidence base for specific recommendations on how long to wait before testing for different STIs is limited, and state ‘for bacterial STIs, many clinicians would wait 3-7 days before testing (level IV)’(3)

Given pressure to meet GUM 48 hour access targets, it may be that a greater proportion of patients present to GUM clinics too soon after exposure to detect or exclude the infection. The need to consider a second test after baseline testing should therefore be borne in mind. We would NOT agree with the statement in the local NCSP poster, which effectively advises patients to defer testing, a strategy which runs counter to the public health arguments for rapid access to GUM clinics.

We ask the question ‘What is a suitable “window period” for chlamydial infection?’ We await guidance from those in a position to undertake the research to answer the question.

If service providers undertake a baseline test and, where relevant, consider a repeat test after a suitable period of time, old and recently acquired infection should be excluded. The recommendation by NCSP for a repeat test after 3-5 weeks appears unrealistic.

The discrepancies between BASHH guidelines and the NCSP Core Requirements and in particular, between NCSP Core Requirements and local delivery of the NCSP, are a cause for concern. Currently, service providers are giving mixed messages. It would be helpful if BASHH and NCSP gave the same steer on this in order to facilitate uniformity of approach at the local level.

Competing interests: None

Corresponding Author:
Dr. Carolyn Rigg
GUM Department,
Southport and Formby District General Hospital
Town Lane
Merseyside, PR9 7LJ
Tel: 01704 547471

Dr. Mike Abbott
GUM Department,
Southport and Formby District General Hospital
Town Lane
Merseyside, PR9 7LJ


1. Low N, Ward H. Focus on chlamydia. Sex Transm Infect 2007;83:251-52.

2. National Chlamydia Screening Programme England: Core Requirements (Third Edition). London: HPA, September 2006. http://www.dh.gov.uk/PolicyAndGuidance/HealthAndSocialCareTopics/SexualHealth/SexualHealthGeneralInformation/SexualHealthGeneralArticle/fs/en?CONTENT_ID=4084098&chk=CSLxsK

3. British Association for Sexual Health and HIV. UK National STI Screening and Testing Guideline, August 2006. http://www.bashh.org/guidelines.asp

Conflict of Interest

None declared