IgG (immunoglobulin G)

Do you frequently have sinus, ear or lung infections and need antibiotics several times a year? IgG testing measures immunoglobulin G, the most abundant antibodies in blood, and shows whether your immune system produces enough protective proteins. Doctors also request it in inflammatory, autoimmune and liver diseases, where IgG may be elevated.

Who is this test for

• adults and children with frequent or severe bacterial infections, for example sinus, ear, bronchial or lung infections that recur or are slow to resolve;
• people in whom a doctor suspects weakened immunity, together with IgA and IgMtests;
• people with chronic liver disease or autoimmune disease, such as rheumatoid arthritis, lupus or Sjögren’s syndrome;
• when total blood proteins are elevated or protein electrophoresis shows an abnormality;
• people who have taken immunosuppressive medicines for a long time, for example corticosteroids or certain biological medicines;
• people receiving immunoglobulin replacement therapy, to monitor levels.

What the test reveals

Immunoglobulin G accounts for around 75 % of all antibodies in blood. The body produces it after infection or vaccination; it “remembers” the pathogen for a long time and protects you when you encounter it again. Only IgG crosses the placenta: a newborn receives it from the mother and gradually produces its own IgG, reaching adult levels only after several years.

The test measures total IgG, meaning all antibodies of this type together. This is not the same as IgG antibodies to a specific virus, such as CMV or EBV, or a food IgG test. Total IgG shows how many antibodies your body produces overall.

The test and preparation

The sample is venous blood. Fasting is not required and blood can be taken at any time of day. Collection takes a few minutes. Tell us if you receive immunoglobulins, have recently received blood or plasma, and which medicines you take, because these may affect the result.

What your results mean

The reference interval depends on age and method and is printed on the report. In adults it is usually approximately 7 to 16 g/L; children have lower values. A doctor interprets the result alongside your symptoms, IgA, IgM and other findings.

• Low IgG may mean that the body produces too few antibodies. The cause may be a congenital antibody deficiency, but medicines, protein loss through the kidneys or intestines, and certain blood diseases are more common causes. In infants between the third and sixth month, IgG is naturally lower because maternal antibodies are disappearing while their own are only beginning to rise.
• High IgG usually accompanies prolonged inflammation: chronic infection, liver disease or autoimmune disease. More rarely, one group of cells produces an excess, which a doctor distinguishes through protein electrophoresis and other tests.
• Normal IgG with frequent infections does not exclude every immune disorder. If symptoms persist, a doctor may suggest further investigations.

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.

Frequently asked questions

Is total IgG the same as a food IgG test?

No. Total IgG shows how many antibodies the body produces overall. A food IgG test measures antibodies to individual foods and is not a diagnosis of allergy or intolerance.

What does “IgG positive” mean on a report for a virus?

This is a different test. Positive IgG antibodies to a specific virus usually mean that you have recovered from the infection or been vaccinated. Total IgG says nothing about this.

Can low IgG be the reason for frequent colds?

Rarely. Children in nursery may have around ten viral colds a year with normal immunity. Recurrent bacterial infections, more severe pneumonia or infections responding poorly to antibiotics are more suggestive of antibody deficiency.

Should IgA and IgM also be tested alongside IgG?

Usually yes when weakened immunity is suspected, because the three immunoglobulins are interpreted together. Your doctor will decide which other tests you need.