Immunoglobulin G Test - IgG

The immune system of our body protects us from bacteria, viruses, and other microorganisms. In response to these disease-causing organisms, our immune system produces specific proteins called immunoglobulins. These immunoglobulins protect us from infection. The test, which measures the amount of Ig proteins in the blood, saliva, or cerebrospinal fluid (CSF) (fluid surrounded by the brain and spinal cord), is the immunoglobulin G (IgG) test.

When disease-causing microorganisms or foreign substances (also known as antigens) infect a person, our immune system recognises it. The immune system cells produce specific immunoglobulins (also called antibodies) against the antigens. When the same infection re-occurs, our body remembers it and produces more antibodies rapidly to prevent the re-infection.

Our immune system produces five types of immunoglobulins:

• Immunoglobulin M (IgM)
• Immunoglobulin G (IgG)
• Immunoglobulin A (IgA)
• Immunoglobulin D (IgD)
• Immunoglobulin E (IgE)

Immunoglobulin G (IgG) is the most common type of antibody present in the body. It is found in all body fluids and comprises 70-80% of all immunoglobulins present in the body. IgG provides long-term protection against infection. They memorise the microorganisms and develop specific antibodies against them. They also prevent the recurrence of the infection. It is the only immunoglobulin that can pass from mother to baby through the placenta during pregnancy. IgG from the mother protects the baby in the first few months after birth. There are four subclasses of IgG:

• IgG1
• IgG2
• IgG3
• IgG4.

The immunoglobulin test measures the amount of each Ig: IgA, IgM, and IgG. Separate testing is done to measure the subclasses of IgG. If the levels of Ig are low or high, it may indicate the presence of some health problem. The test shows whether the immune system of our body is working correctly. If the level is low, the immune response is low, and there are more chances of getting an infection. A high level means the immune response is overactive, and you could have allergies.

Symptoms for deficiency or excess of IgG differ greatly. There may be frequent infections, fever, skin rashes, sinus infection, diarrhoea, allergies, or a lung infection. The IgG test is also prescribed if you have a family history of immunodeficiency. It can detect bacterial infections, low immunity, autoimmune disorders, cancers like multiple myeloma, and also infections in newborns.

IgG tests are easily available in India. Recently, during the COVID-19 pandemic, the antibody IgG test was used to determine the presence or absence of antibodies after the infection and vaccination. IgG antibodies usually become positive after 8 - 13 days of infection and peak around 21 days.

The test is not used to diagnose the active infection though.

The IgG Test requires a blood sample. In some cases, the test is done using other body fluids, like CSF or saliva.

Pneumonia, Multiple myeloma, Rheumatoid arthritis, Leukaemia, HIV/AIDS

The IgG Test measures the levels of immunoglobulin G in the body.

If a person is experiencing the following conditions, doctors may ask you to get an IgG Test:

• Unexplained weight loss
• Diarrhoea for a long time (Chronic Diarrhoea )
• Frequent fever
• Frequent infections
• Skin rashes
• Allergies
• Sinus infection

In such cases, an IgG Test is prescribed by the physician to check the level of immunity. It can also be prescribed to check the presence of antibodies after the body recovers from the infection.

There are some disease conditions for which an Immunoglobulin G Test is prescribed are:

• Multiple myeloma
• HIV/AIDS infection
• Leukaemia
• Pneumonia
• Autoimmune disorders like Rheumatoid arthritis
• Family history of immunodeficiency
• Infection in lungs, stomach, or intestine
• Chronic illness
• Post recovery from illness
• Post-vaccination

The IgG Test is for both males and females of all ages. Its results are affected by alcohol, use of certain medications for seizures and arthritis, vaccination in the past 6 months, a booster dose of vaccine, radiation, and chemotherapy. Consult your doctor and tell them about all the ongoing medications and treatments.

Your doctor will prescribe the Immunoglobulin G Test according to your health status. The quantitative Immunoglobulin Test, along with other tests, helps with the diagnosis of the disease that affects the body's immune system. Once the medication has started, the health practitioner may prescribe the IgG test at regular intervals to assess the body's antibodies and immune response.

Before the Test

Before undergoing the IgG Test, it is unlikely that your doctor will require you to take any special precautions. However, if you are to take this test with another one that requires special preparation, your doctor may suggest fasting for a specific time. Always speak with your doctor before a test.

During the Test

For the IgG Test, the phlebotomist will take a blood sample from your arm. Here's what will happen during the test:

• The likely puncture site will be sterilised with antiseptic.
• A tourniquet will be secured around your arm to make your veins stand out.
• A needle will be inserted into a chosen vein to draw the blood. This may cause a brief pinch for a few seconds.
• The blood will be collected in a vial/small test tube, and a label will be affixed with your details.

After the Test

Following the blood collection:

• A bandage will be placed over the insertion site to stem any bleeding.
• Bruising can happen. If you feel lightheaded (an uncommon side effect), you may be advised to rest for a few minutes.
• In case of persistent bleeding, pain, or rashes at the puncture site, contact your doctor.

The IgG Test parameter includes the range of immunoglobulin G in the blood. The result of this test shows the amount of IgG in g/L or mg/dL. If the value is at the low side of the range, it suggests low immunity. If the value is on the higher side, it suggests an overactive immune system. The IgG Test results are also described as positive or negative IgG regarding the presence or absence of IgG antibodies in the body.

The test does not diagnose any disease or condition. It shows the level of immunity. Along with other tests, it helps in the diagnosis and management of a disease.

During the initial days of pregnancy, the IgG level increases and after 20 weeks it becomes normal. Females tend to have higher levels of IgG compared to males.

The normal values and reference ranges of the test may vary from lab to lab. Please refer to the ranges mentioned in the report and consult a doctor to understand the interpretation of lab reports.

The following interpretation of the IgG Test can be made as per the range.

If the result of the Immunoglobulin G Test shows a lower value of the IgG than the normal, it may be indicative of:

• Kidney disease
• Malnutrition
• Diabetes complications
• Severe burn injury
• Weakened immunity like in HIV/AIDS infection

If the result of the Immunoglobulin G Test shows a higher value of the IgG than the normal, it may be indicative of:

• Autoimmune disorder
• Hepatitis
• Multiple Myeloma(type of cancer)
• Cirrhosis
• Liver disease
• Allergies
• Chronic infection

If the test results are not normal, it doesn't mean you have the above mentioned conditions. It means that your immune response is either high or low. The consulting doctor will advise you further according to your condition and test results.

The IgG antibody test can also be determined as positive or negative in response to specific antibodies:

• Positive: if antibodies are present after the infection has passed
• Negative: if antibodies are not present after the infection has passed or no recent back history of infection/disease.