IgM + IgG antibodies to Mycoplasma pneumoniae

Have you or your child had a persistent dry cough, fever and fatigue for days, with only slow improvement? Mycoplasma pneumoniae is a common cause of “walking” pneumonia, particularly in schoolchildren and young people. IgM and IgG antibody testing helps a doctor determine whether mycoplasma is causing symptoms and choose an effective antibiotic.

Who is this test for

• children, young people and adults with a persistent dry cough, fever, sore throat and fatigue;
• for pneumonia that does not respond to amoxicillin or other usual antibiotics;
• when a similar infection is spreading in the family, classroom or nursery;
• for a cough lasting weeks after a respiratory infection;
• for a rash, ear infection or other symptoms outside the lungs that a doctor associates with mycoplasma;
• during periods of increased mycoplasma spread, which recur every few years.

If you or your child have rapid or difficult breathing, bluish lips, inadequate fluid intake or unusual sleepiness in a child, seek medical attention immediately or call 194 or 112.

What the test reveals

Mycoplasma pneumoniae is a bacterium without a cell wall, which is why penicillins and related antibiotics do not work against it. It spreads through droplets during close contact, and illness usually begins one to four weeks after infection. The illness is usually mild and many recover without hospital admission, but the cough may last for weeks.

The test measures two types of antibodies. IgM usually appears around a week after symptoms begin, with IgG somewhat later. IgM may remain positive for months and may sometimes be absent in adults with repeat infection. The test is therefore most useful in children and young people and when a doctor compares two blood samples.

The test and preparation

A venous blood sample is taken, and fasting is not required. Collection takes a few minutes and is adapted to a child’s age. Antibodies develop gradually and may still be negative during the first days of illness. A doctor sometimes requests a second sample after two to four weeks to see whether IgG rises. Early in the illness, they may also request throat-swab PCR, which detects the bacterium directly.

What your results mean

• Positive IgM: with typical symptoms suggests a recent infection, particularly in children. Since IgM may remain positive for months, it does not by itself prove that mycoplasma is causing current symptoms.
• Only IgG positive: usually means a past infection. A rise in IgG in the second sample suggests a recent infection.
• IgM and IgG negative: mycoplasma infection is unlikely, but antibodies may not yet have formed during the first week of illness.

A doctor interprets the result alongside examination, the course of illness and a chest X-ray if needed. They also decide on treatment, because some mycoplasmas respond less well to certain antibiotics.

How to arrange testing

You can come for blood collection without an appointment or referral at one of our branches throughout Croatia (listed on the Contactpage). Prices for all tests and panels are listed in the price list. From the same blood collection, a doctor may also request antibodies to Chlamydia pneumoniae, another common cause of atypical pneumonia.

Frequently asked questions

Is mycoplasma contagious?

Yes. It spreads through droplets from coughing and sneezing, most often among household members, at school and in nursery. Because several weeks pass between infection and illness, it spreads gradually through a family.

Is this the same mycoplasma tested for in a swab?

No. Mycoplasma pneumoniae affects the respiratory tract. Mycoplasma genitalium and Mycoplasma hominis occur in the genital and urinary tract and are detected by a different test, PCR from urine or a swab.

How long does the cough last?

The cough with mycoplasma often lasts several weeks, sometimes even after treatment is complete. If it worsens, fever returns or breathing becomes more difficult, contact a doctor.

Is follow-up testing needed after treatment?

Usually not. Antibodies remain in blood after recovery, so they do not show whether treatment succeeded. A doctor assesses recovery through symptoms and examination.