Chlamydia pneumoniae IgM + IgG antibodies

Have you been coughing for weeks after a cold, with pneumonia or bronchitis not resolving as expected? IgM and IgG antibody testing for Chlamydia pneumoniae shows whether your body has encountered this common cause of “atypical” pneumonia recently or previously. Results help a doctor assess whether symptoms are caused by bacteria unaffected by some common antibiotics such as amoxicillin.

Who the test is for

• people with a dry persistent cough lasting weeks after a respiratory infection;
• for milder pneumonia developing gradually with sore throat, hoarseness, headache and fatigue;
• when usual antibiotic treatment does not improve symptoms;
• for slow-resolving bronchitis, pharyngitis or sinusitis;
• people with asthma or chronic lung disease whose symptoms worsen after infection;
• when similar infection spreads in a family, school, care home or other group.

For difficulty breathing, chest pain, persistent high fever or bluish lips, seek medical attention immediately or call 194 or 112.

What the test reveals

Chlamydia pneumoniae is a bacterium spread by coughing and sneezing droplets that affects the respiratory tract. Illness usually develops gradually and is often mild, but coughing can last weeks. Most people have the infection at least once, often unknowingly, so antibodies are common in adults.

The test measures two antibody types. IgM develop early in a first infection, usually around three weeks after illness begins. IgG appear later in a first infection, after six to eight weeks, and can remain for years. In reinfection IgM are often absent and IgG rise quickly.

The procedure and preparation

Blood is taken from a vein and fasting is unnecessary. Collection takes a few minutes. Because antibodies develop gradually, testing is most useful several weeks after symptoms begin. A doctor sometimes requests a second sample after four to eight weeks to compare IgG levels. Remember symptom onset because it matters for interpretation.

What your result means

• Positive IgM: suggest recent infection, particularly with typical symptoms. A false-positive result is possible, so a doctor assesses it alongside the illness course.
• IgG positive alone: most often means previous infection. A single positive IgG does not establish current illness; recent infection requires a significant IgG rise between two samples.
• IgM and IgG negative: infection is unlikely, but antibodies may not yet have developed early in illness.

A doctor interprets results alongside examination and illness course, referring if necessary for a chest X-ray or swab PCR directly demonstrating the bacterium.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). Prices for all tests and panels are available in the price list. From the same collection a doctor may also request antibodies to Mycoplasma pneumoniae, another common atypical pneumonia cause.

Frequently asked questions

Is Chlamydia pneumoniae sexually transmitted?

No. It is a respiratory bacterium. The related but different sexually transmitted bacterium is Chlamydia trachomatis, detected using chlamydia PCR testing.

What does positive IgG with negative IgM mean?

Most often a past infection. Many healthy adults have this result and without symptoms it requires no treatment.

Should testing be repeated after treatment?

Usually not. Antibodies persist for months or years after recovery, so do not show whether treatment worked. Success is assessed through symptoms and examination.

Is the infection contagious?

Yes, through droplets, but slowly because illness usually develops several weeks after infection. Cover your mouth when coughing and wash hands frequently, particularly around older people and those with chronic conditions.