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Chlamydia IgG

Chlamydia IgG: antibodies against chlamydia and the difference with an STI test on urine

According to the RIVM, chlamydia infections of the genitals and urinary tract are the most common bacterial STI in Western countries, and the immune system responds to that bacterium with antibodies, proteins that fight germs. According to MedlinePlus, IgG is the kind of antibody the body keeps recognising even after an infection has cleared.

Chlamydia antibodies in the blood can fit a current infection and an infection that has already cleared or been treated, according to the RIVM, and the blood test makes no distinction between the two. Chlamydia antibodies only become visible with a blood test.

The expected result is 'negative' at Star-SHL and Diagnostiek voor U, without a unit, and the test is done in serum.

Doctor's Assessment Included

The chlamydia IgG test looks in the blood for antibodies against chlamydia, which the body makes after contact with the bacterium. Normally the result is negative.

A chlamydia antibody test cannot tell an earlier infection from one that is still active; for a current infection, a PCR test on urine or a swab is the usual test.
A negative chlamydia antibody test does not rule out an infection: not everyone makes measurable antibodies, and the test is less sensitive than a PCR test.
In a fertility work-up, a positive chlamydia antibody test (CAT) counts as a risk factor for damage to the fallopian tubes.

Reference Ranges

Expected result Negative

Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.

Chlamydia IgG: what this test measures

The chlamydia IgG test measures whether the serum contains IgG antibodies against chlamydia, with positive or negative as the result. A chlamydia IgG test looks for the immune response to the bacterium, while a NAAT detects genetic material of the bacterium itself in urine or a swab, according to the RIVM.

Chlamydia IgG: why this value matters

Chlamydia often causes no symptoms: according to the RIVM, 70 to 95% of chlamydia infections in women run without symptoms, and more than half in men. According to the RIVM, an earlier chlamydia infection does not protect against a new infection and raises the chance of complications, possibly through a stronger immune response.

Chlamydia IgG: how the blood test works

Referral: No GP referral needed. After the order we arrange the referral through ZorgDomein, within one business day; orders after 17:00 or at the weekend start on the next business day. ZorgDomein emails a barcode, and that barcode is what the draw site needs.
The draw: A blood draw from a vein in the arm, at a partner laboratory's draw site. No home kit, no finger prick.
Where: 650+ draw sites run by independent laboratories across the Netherlands. Draw sites

Chlamydia IgG: when is testing worthwhile?

After possible contact with chlamydia, a NAAT on urine or a swab is the usual test according to the RIVM, and it gives a reliable result two weeks after transmission. According to the RIVM, a chlamydia antibody test is less sensitive and less accurate than a NAAT and therefore has a limited place in diagnosing an infection.

Chlamydia IgG: symptoms of a high or low value

Low Levels

A negative chlamydia IgG result means that the test found no antibodies, which is the expected result. A negative chlamydia IgG result does not rule out a recent infection, because for a current infection an antibody test is less sensitive than a NAAT, according to the RIVM.

High Levels

A positive chlamydia IgG result means that antibodies against chlamydia were found, from an earlier or a current infection, or from another chlamydia species. In men with chlamydia, the RIVM names burning urination and discharge, among others, as symptoms. According to the RIVM, only a small share of women with chlamydia has symptoms, such as changed discharge, bleeding between periods and pain or bleeding during sex.

Chlamydia IgG: causes of a low or high value

What raises the value

Earlier chlamydia infection

Chlamydia antibodies can come from an infection that has already cleared or been treated.
Current, untreated infection

A chlamydia infection that is still present can also give a positive result; the chlamydia blood test cannot tell a current infection from an earlier one.
Other chlamydia species

Depending on the test, antibodies against other chlamydia species can cross-react, for example antibodies against the airway bacterium Chlamydia pneumoniae; the RIVM notes much cross-reaction between chlamydia species.

Chlamydia IgG: lifestyle and this value

According to the RIVM, consistent condom use reduces the risk of chlamydia transmission, although a condom can tear or slip off, according to the RIVM. When a current chlamydia infection is found, sexual health care is not complete without informing sexual partners, according to the RIVM.

Chlamydia IgG: frequently asked questions

Can a chlamydia blood test replace a urine test?

No, a chlamydia blood test does not replace a urine test: the blood test looks for antibodies and, according to the RIVM, cannot tell a current infection from a cleared one. For a current infection, the RIVM names a NAAT on urine or a swab as the usual test.

How long after sex can chlamydia be detected?

According to the RIVM, chlamydia can be reliably detected two weeks after transmission with a NAAT on urine or a swab. The LCI guideline gives no time frame for the chlamydia antibody test in the blood.

Can you get chlamydia twice?

Yes, chlamydia can come back: an earlier chlamydia infection does not protect against a new infection, according to the RIVM. According to the RIVM, repeated infections raise the chance of complications.

Chlamydia IgG: sources

RIVM, LCI-richtlijn Chlamydia trachomatis en lymphogranuloma venereum, vastgesteld 25 juni 2024, geraadpleegd 2026-10-05 (retrieved 2026) lci.rivm.nl
RIVM, LCI-richtlijn Chlamydia pneumoniae, hoofdstuk Diagnostiek vastgesteld 5 april 2019, geraadpleegd 2026-10-05 (retrieved 2026) lci.rivm.nl