PIGN is the most common type of glomerulonephritis affecting children. 

What happens in the kidneys

In PIGN, the tiny kidney filters (glomeruli) become inflamed (swollen) or damanged. Thet leak blood cells and protein into the urine

Read more about how kidneys work and PIGN

Inside each kidney, there are about one million nephrons. Each nephron is made up of a glomerulus (when we talk about more than one glomerulus, we say glomeruli), and a renal tubule.

  • Each glomerulus acts like a sieve, helping to remove extra water and waste from the body, and holding on to blood cells and protein, which the body needs.
  • Blood flows into the kidneys and to each glomerulus.
  • Most of the water and some other substances in the blood pass through the glomeruli.
  • This liquid flows into the renal tubule. Most of this liquid moves back into the bloodstream. The rest of it becomes urine.
  • The urine leaves the kidney by the ureters and goes into the bladder, where it is stored until we are ready to go to the toilet.

About the urinary system and kidneys – what the kidney does

What happens in PIGN

In PIGN and other types of glomerulonephritis, the glomeruli become inflamed (swollen) or damaged. The damaged glomeruli can let blood cells and protein through, which means they go into the urine.

About the name 

Nephritis means inflammation, or swelling, in the kidneys. Glomerulonephritis is specifically about inflammation of the glomeruli.

After infection

PIGN is called post-infectious because it usually happens after an infection. The infection is not in the kidney, but rather a different part of the body, such as the throat, nose or sinuses (this may be called strep throat), or the skin (this may include impetigo). The infection is often caused by a particular bacterium (germ) called Streptococcus. When glomerulonephritis appears after an infection from Streptococcus, the condition is often called post-streptococcal glomerulonephritis (PSGN).

Most children recover from these infections. However, a very small number of children get glomerulonephritis after about two weeks from the start of the infection. It is not always clear why a few children get this condition after an infection.

The immune system

Many germs – including bacteria and viruses – can make us sick if they get into the body. The immune system can kill these germs. However, if the immune system is not working properly, it can start to cause problems.

Read more about the immune system


The immune system protects the body against germs such as bacteria and viruses that can cause illness. These germs can enter the body in lots of ways, such as by the nose and throat or the urinary system. If we get a cold or flu, this means that a virus germ has got into the body and started to infect some of our body’s cells.

Germs have special ‘markers’ that are different from the markers on our own body’s cells. This means that the immune system can recognise that they are germs and kill them. We often feel sick for a few days or a few weeks while this is happening.

Parts of the immune system

The immune system has many different ways to protect the body against disease. Some of the parts include those listed below.

  • White blood cells are living cells in the blood. Often, the number of white blood cells found in a blood test can give information about someone’s immune system. The two main types of white blood cells in the immune system are neutrophils and lymphocytes.
  • Antibodies or immunoglobulins recognise the germs that have come into the body, and can bind (stick) to them. There are five types: immunoglobulin A (IgA), immunoglobulin D (IgD), immunoglobulin E (IgE), immunoglobulin G (IgG) and immunoglobulin M (IgM).
  • The complement system is made up of other proteins that float in the blood. These proteins work with (complement) other parts of the immune system to help kill germs or cells infected by germs. Normally, the body controls when complement is activated, so it does not attack the body itself.

When the immune system does not work properly

Sometimes the immune system does not work as expected and can cause problems. For example, sometimes the immune system cannot recognise the body’s own cells and may attack them as if they were invaders like germs.

Will it affect other family members?

Doctors do not think that PIGN runs in families. If one of your children has this type of glomerulonephritis, it is unlikely that another of your children or another family member will get it. 

Your child will need some tests to diagnose (identify) PIGN, find out more about how it is affecting him or her and whether any treatment is needed. Your child may need an examination, urine tests, blood tests, imaging tests and a kidney biopsy.

Your doctor will talk to you or your child about his or her symptoms and any medicines that he or she takes. The doctor will examine your child – for example, to see whether there is oedema (swelling in the body).

Your doctor or nurse will check your child’s blood pressure. This is because PIGN may cause high blood pressure (hypertension).

Urine tests

You or a nurse will need to collect some of your child’s urine in a small, clean container for a urine test. A dipstick will be dipped into the urine – this is a strip with chemical pads that change colour depending on what substances are in the urine. This shows whether there are blood cells and/or protein, which are signs of PIGN.

The sample may also be sent to a laboratory for more accurate tests.

Blood tests

A small amount of blood will be taken from a vein, with a needle and syringe, for a blood test. A special gel or cream can be used to help your child from feeling any pain. The blood test results can give the doctor more information, including:

  • about the immune system, and whether your child has had a recent infection
  • how well his or her kidneys are working – this is called the kidney function
  • the amount of protein in your child’s blood – in PIGN, the kidneys leak protein into urine but this is not normally enough to affect how much is in the blood
  • the amount of types of blood cells and other chemicals.

Read more about blood tests for PIGN

What blood tests measure

  • A blood test can check whether there are any antibodies, which the body’s immune system makes to identify and kill specific germs. This gives information about whether there has been an infection, and sometimes which germ caused it.
  • Children with PIGN may have low levels of a protein called complement C3, which is also part of the immune system. This complement works with antibodies to help kill cells infected by germs.
  • The amount of urea and creatinine can be measured. These are waste products made in the body, which are normally removed by the kidneys into urine.
  • The kidney function can be measured by glomerular filtration rate (GFR). The GFR is the amount of fluid the kidneys cannot filter each time. It can be estimated by measuring the amount of creatinine in the blood. 
  • The amounts of different types of blood cells can be measured in a full blood count. 

Other chemicals

Electrolytes are important chemicals in the body. We need the right balance of these to stay healthy. Some important electrolytes include the following:

  • sodium helps balance the amount of water in the body
  • potassium is needed for the muscles, including the heart muscle, to work properly
  • bicarbonate balances the amount of acid in our body, or the pH balance (also called the acid–base balance)
  • phosphate is important for bones, teeth and muscles
  • calcium is important for bones and teeth, helps blood to clot and also helps the muscles, including the heart muscle, to work.

Imaging tests

Some children need imaging tests (scans). These use special equipment to get images (pictures) of the inside of the body.

  • Ultrasound scan – looks at the shape and size of kidneys and other parts of the urinary system.  A small handheld device is moved around your child’s skin and uses sound waves to create an image on a screen.  
  • Chest X-ray – for children with breathing problems, a chest X-ray checks for any fluid (liquid) around the lungs. Your child sits or lies still for a few seconds while a machine takes X-ray images.

Occasionally, other imaging tests are needed.

Kidney biopsy

Your doctor may recommend a kidney biopsy to find out how PIGN is affecting the kidneys or whether your child has another type of glomerulonephritis. A tiny piece of one kidney is removed from the body with a needle and examined under microscopes. 

Medicines are used so your child does not feel any pain or can sleep through the procedure. It can take a few weeks to get the results.