Chlamydia trachomatis IgG

Chlamydia is an STI caused by the bacterium Chlamydia trachomatis. After an infection, the immune system makes IgG antibodies against the bacterium, which can remain present for years, even when the infection has long gone. This test measures those antibodies in the blood. So it shows whether you have ever had a chlamydia infection, not whether the bacterium is present now; for that, a PCR on urine or a swab is needed. According to the Dutch guideline on initial fertility testing, a positive result in women who are not getting pregnant fits an increased chance of damaged fallopian tubes.

• A past chlamydia infection, even if it never caused symptoms
• In women who are not getting pregnant: an increased chance of damaged or blocked fallopian tubes due to a past infection

With a positive result and a wish to have children, the GP or gynecologist assesses, together with the medical history, whether testing of the fallopian tubes is needed, for example with an X-ray using contrast fluid (HSG). A positive antibody test is no reason for antibiotics; with symptoms or a risky sexual contact, a PCR comes first. Individual cases of chlamydia are not notifiable.

Antibodies against chlamydia show a reaction of the immune system to a past infection, not the bacterium itself; according to the LCI guideline (RIVM), the test for a current infection is a PCR on urine or a swab. According to the Dutch guideline on initial fertility testing, a positive result, or a past pelvic inflammation, goes with an increased chance of damage to the fallopian tubes, and further testing of the fallopian tubes is then the next step; with a negative result and no such history, that chance is low. The result is a weighing of the chance, not a diagnosis.

• The antibodies remain present for years after an infection and say nothing about an infection at this moment.
• Shortly after an infection is passed on, antibodies cannot be detected yet, and not everyone makes them.
• Depending on the test, a cross-reaction with Chlamydia pneumoniae, a cause of respiratory infections, can give a falsely positive result.
• The result does not say where the infection was, nor whether the fallopian tubes are actually damaged.

Chlamydia is the most common bacterial STI in the Netherlands. In 2024, the sexual health centers of the GGD (municipal public health service) found chlamydia in 20,174 people, two thirds of whom had no symptoms; GPs made the diagnosis about 43,000 times in 2023. Chlamydia is most common in young people under 25, and many infections are never noticed.

The result says the most in women who have not become pregnant for more than a year, as part of the search for the cause; it then helps to estimate whether testing of the fallopian tubes is useful. With symptoms that fit chlamydia or after a risky sexual contact, this test says nothing about an infection at this moment; a PCR on urine or a swab then says more. In people without symptoms and without a wish to have children, the result changes little.

• A positive result can cause worry about fertility, while most people with antibodies do not have damaged fallopian tubes.
• The result can wrongly be read as a sign of an infection at this moment, or, on the contrary, wrongly reassure you after a recent risky sexual contact.

• RIVM-LCI-richtlijn Chlamydia trachomatis en lymphogranuloma venereum
• FMS Richtlijnendatabase: Oriënterend fertiliteitsonderzoek (OFO), module Tubadiagnostiek
• Thuisarts.nl: Chlamydia
• Thuisarts.nl: Zwanger worden lukt niet
• RIVM: Chlamydia (cijfers 2024)