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Chlamydia IgG: what antibodies against chlamydia in the blood do and do not tell you

Antibodies are proteins that the immune system makes to fight germs such as viruses and bacteria. According to MedlinePlus, the patient site of the US National Library of Medicine, IgG is the kind of antibody the body makes against one specific germ and keeps remembering after an infection has cleared. Chlamydia IgG are such antibodies against chlamydia bacteria.

A positive result means that antibodies against chlamydia are in the blood, but according to the LCI guideline of the Dutch public health institute RIVM, an antibody response cannot tell a current infection from one that has already cleared or been treated. Only a blood test shows whether chlamydia antibodies are in the blood.

Star-SHL and Diagnostiek voor U give 'negative' as the expected result, without a unit, and Unilabs lists no reference value for its chlamydia antibody tests.

Turnaround 48 hours, estimate Turnaround: up to 48 hours after your blood draw (estimate).

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 values can vary between laboratories. Discuss your results with your GP for explanation and treatment decisions.

Chlamydia IgG: what this test measures

The chlamydia IgG test measures whether IgG antibodies against chlamydia are present in the serum, and the result is positive or negative, without a unit. Star-SHL calls its test 'Chlamydia species IgG'.

According to the RIVM, antibodies against the different chlamydia species cross-react a great deal. A chlamydia antibody test can therefore also turn positive through antibodies against a chlamydia species other than the sexually transmitted bacterium.

Chlamydia IgG: why this value matters

Chlamydia often causes no symptoms: according to the RIVM, that holds for up to 90% of chlamydia infections of the urinary tract and genitals. In women, an infection can rise and cause inflammations of, among others, the lining of the womb and the fallopian tubes, together called pelvic inflammatory disease (PID), according to the RIVM. According to the RIVM, the consequences of PID can be chronic lower abdominal pain, reduced fertility, infertility and an ectopic pregnancy.

In a fertility work-up, a positive chlamydia antibody test (CAT) counts as a risk factor for damage to the fallopian tubes, according to the guideline of the Dutch Society of Obstetrics and Gynaecology (NVOG).

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.
Results
Turnaround: up to 48 hours after your blood draw (estimate).
Where
650+ draw sites run by independent laboratories across the Netherlands. Draw sites

Chlamydia IgG: when is testing worthwhile?

A chlamydia antibody test (CAT) has a place in the initial fertility work-up: the NVOG guideline recommends an examination of whether the fallopian tubes are open, the HSG, after a positive CAT or a past PID.

For a possible current chlamydia infection, a NAAT is the usual test according to the RIVM, a test that detects genetic material of the bacterium in urine or a swab. According to the RIVM, a NAAT gives a reliable result two weeks after transmission, and antibody tests are less sensitive and less accurate than a NAAT.

Chlamydia IgG: symptoms of a high or low value

Low Levels

A negative chlamydia IgG result means that the test found no antibodies against chlamydia, and that is the expected result at Star-SHL and Diagnostiek voor U. A negative result does not rule out a current or an earlier infection: in an English study of women attending sexual health clinics, a research antibody test found antibodies in 57.1% on the day of a first chlamydia diagnosis.

High Levels

A positive chlamydia IgG result means that the blood contains antibodies against chlamydia, coming from an earlier infection, a current infection or another chlamydia species. According to the LCI guideline of the RIVM, the blood test cannot say whether it is an earlier or a current infection.

According to the RIVM, a small share of women with chlamydia has symptoms, such as painful or burning urination, changed discharge, bleeding between periods, pain or bleeding during sex and pain in the lower abdomen. In men with chlamydia, the RIVM names burning urination, watery to pus-like discharge and sometimes pain in the scrotum. According to the RIVM, PID is often marked by a tender abdomen, fever and general malaise.

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

Condoms can protect against the sexual transmission of chlamydia, according to the RIVM, and consistent condom use reduces the risk of transmission. When a current chlamydia infection is found, sexual health care is not complete without informing sexual partners, partner notification, according to the RIVM.

A positive chlamydia IgG result with symptoms, a recent risk or a fertility question is one to discuss with your GP; for a current infection, a NAAT on urine or a swab is the usual test according to the RIVM.

Chlamydia IgG: frequently asked questions

Does a positive chlamydia IgG result mean there is an infection now?

No, not necessarily: according to the RIVM, a positive chlamydia IgG result fits a current infection and an infection that has already cleared or been treated, and the blood test cannot tell the two apart. According to the RIVM, a NAAT on urine or a swab is the usual test for a current infection.

Does a negative chlamydia IgG result rule out an earlier infection?

No, a negative chlamydia IgG result does not rule out an earlier infection. In an English study of women attending sexual health clinics, the share with antibodies on one research test fell to 49.3% two or more years after a first diagnosis.

Do chlamydia antibodies protect against a new infection?

No, chlamydia antibodies from an earlier infection do not protect against a new infection, according to the RIVM. According to the RIVM, earlier infections actually raise the chance of complications, possibly through a stronger immune response.

Chlamydia IgG: sources

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

Tests with related values

These panels measure values from the same category as this marker.

Results without a doctor's assessment

You receive your values with the unit and reference range. A doctor's assessment is not part of this site. Discuss your results with your GP for explanation and treatment decisions.

Chlamydia IgG

€49,-