Important chemicals
We need the right balance of chemicals to stay healthy. Your child’s blood will be checked to find out if they have too much or too little of any of these chemicals.
Urea and creatinine
The body makes some chemicals after it uses energy. Urea is made from the food we eat, and creatinine is made when we use our muscles. These are waste products, and the kidneys remove them from the body into urine.
If there is too much urea or creatinine in the blood, this may be a sign that the kidneys are not working as well as they should.
Electrolytes
These chemicals help make sure that the muscles, heart bones, teeth and blood, are healthy.
- Sodium helps balance the amount of water in the body.
- Potassium is needed for muscles, including the heart, to work properly.
- Bicarbonate balances the amount of acid in our body.
- 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, to work.
Other substances
Blood tests can be used to look for other substances.
- Vitamin D helps the body take in calcium, which helps children to grow. We can get vitamin D from food and sunlight. The kidneys change the vitamin D to an active form that our bodies can use.
- Serum albumin is the main protein in blood. It helps control the amount of water inside blood vessels.
- Parathyroid hormone (PTH) is a hormone – a chemical carried in the blood that sends message to other parts of the body. PTH controls the amount of calcium, phosphorus and vitamin D levels in the blood and bone.
- Glucose is a form of sugar.
- Cholesterol is a type of fat.
Infection and immune system function
Blood cultures check if the blood sample has any germs in it.
Immunology tests look for antibodies. When germs come into the body, the body makes antibodies to kill them. This gives the body immunity to this type of infection.
These tests can help find out if your child has or has had an infection such as chicken pox. They can also show if there are problems with the immune system the body’s way of defending itself against infection and disease.
Some people have autoimmune conditions where antibodies attack the body’s own tissues and organs.
Full blood count
In a full blood count (FBC) or a complete blood count (CBC) blood is examined under a microscope and the amounts of different blood cells are measured. This includes:
Haemoglobin: a protein in the red blood cells which carries oxygen round the body and removes carbon dioxide. If the amount of haemoglobin is below the normal level, or if there are fewer red blood cells than normal, this is called anaemia. Anaemia is a common complication of some kidney conditions, including chronic kidney disease.
White blood cells: help the body fight infections. If there is a higher than normal number of white blood cells, there may be an infection. If there is a lower than normal number this may mean that the body is not able fight infection effectively.
Platelets: help to prevent excessive bleeding – for example, when we graze our skin.
Occasionally, certain medicines mean that the bone marrow does not make as many blood cells as it should. Measuring the FBC helps check if this is happening.
Blood group
If your child needs to receive blood or a new kidney from a donor (someone who gives blood or donates one of their kidneys), it is important to find out their blood group. This is because the blood groups need to match.
Your blood group is based on whether you have certain substances on your red blood cells. It is inherited from your mother and father.
Blood groups are defined by two systems:
ABO system – identified by the letters, A, B, O and AB
Rhesus system – identified as either positive or negative. Hospital laboratories will check this as girls who are Rhesus negative need special precautions when given blood transfusions to protect future pregnancies.