Blood chemistry tests

Blood chemistry tests are blood tests that measure amounts of certain chemicals in a sample of blood. They show how well certain organs are working and can help find abnormalities. Blood chemistry tests may also be called chemistry panels.

There are many types of blood chemistry tests. They measure chemicals including enzymes, electrolytes, fats (also called lipids), hormones, sugars, proteins, vitamins and minerals. Often several chemicals are grouped together and measured at the same time.

Different tests may be used to measure different types of chemicals. The following are some common blood chemistry tests you may have.

An electrolyte panel measures sodium, potassium, chloride, magnesium, phosphate and bicarbonate.

Kidney function tests (also called a renal panel) measure blood urea nitrogen (BUN) and creatinine.

Liver function tests measure alanine aminotransferase (ALT), alkaline phosphatase (ALP), aspartate transaminase (AST), bilirubin, albumin and total protein.

A basic metabolic panel (BMP) includes an electrolyte panel and kidney function tests and also measures glucose and calcium.

A comprehensive metabolic panel (CMP) includes an electrolyte panel, kidney function tests and liver function tests and also measures glucose and calcium.

Blood chemistry tests are common blood tests. They are often done as part of a routine checkup, but can be done at any time.

Blood chemistry tests can be done to:

• learn information about your general health
• check how certain organs are working, such as the kidneys, liver and thyroid
• check the body’s electrolyte balance
• help diagnose diseases and conditions
• provide the levels of chemicals (a baseline) to compare with future blood chemistry tests
• check how a treatment is affecting certain organs
• monitor cancer or another condition (as a part of follow-up)

How you prepare for blood chemistry tests depends of the type of chemical being measured. If needed, you will be given special instructions to follow before having blood chemistry tests.

You may be told not to eat or drink anything (except water) for several hours before having blood chemistry tests. This is called fasting.

Some medicines may also affect blood chemistry test results. You may be asked to stop taking certain medicines before having blood chemistry tests. Check if you should avoid any medicines and for how long.

Blood chemistry tests are usually done in a community lab or hospital.

Blood is usually taken from a vein in the arm. An elastic band (a tourniquet) is wrapped around your upper arm to apply pressure to the area and make the veins easier to see. You may be asked to make a fist so the veins stand out more. The skin is cleaned and disinfected. A needle is inserted into the vein and a small amount of blood is removed. You may feel a prick or stinging sensation.

The blood is collected in a tube and labelled with your name and other identifying information. Sometimes more than one tube of blood is collected. The tourniquet is removed and the needle is withdrawn. You may feel mild discomfort when the needle is withdrawn. Pressure is applied to the area where the needle was inserted until bleeding stops. A small bandage may be put on the area.

The blood collected is then examined by a specialist at the lab (a lab technologist) using microscopes and other special equipment.

Blood chemistry tests do not usually cause any side effects. If side effects happen, they are usually minor and happen at the needle site. Side effects that may happen include:

• discomfort
• bleeding
• bruising
• swelling
• infection

Blood chemistry test results are given as numbers and often depend on certain factors including sex, age and medical history. They should be compared to a normal reference range and to previous results to have meaning.

Some blood chemistry tests show specific health problems. Other blood chemistry tests provide more general information that can give doctors clues to possible health problems. Information from blood chemistry tests may help doctors decide whether other tests or procedures are needed to make a diagnosis. The information may also help your doctor develop or revise treatment plans.

A doctor familiar with your medical history and overall health is the best person to explain your blood chemistry test results and what they mean for you.

Your doctor may recommend more tests, procedures, follow-up care or treatment.

Blood samples may need to be taken from very small blood vessels (called capillaries) in a finger or heel of an infant or young child. This is done by pricking the skin with a needle.

Preparing children before a test or procedure can help lower their anxiety, increase their cooperation and develop their coping skills. This includes explaining to children what will happen during the test, such as what they will see, feel and hear.

Parents or caregivers can help reassure and prepare children by giving them brief but accurate information about what will happen, such as:

• A big rubber band that feels like a balloon will be placed around your arm. This will feel tight, like someone is squeezing your arm.
• When your skin is cleaned it will feel cold.
• When the needle is placed in your arm, you will feel a prick or pinch. It may sting or hurt a little, or it may not hurt at all.
• Once the needle is in your arm, you will see the blood come out into a tube. You can look away if you don’t want to watch this.

Children may worry about not having enough blood after some has been taken from their arm. You can reassure them that bodies make new blood all the time and that their body will not run out of blood.

Parents or caregivers can help distract children during blood tests to help make it easier for them.

Toddlers (1 to 2 years) might like to watch bubbles or toys that move or make sounds, such as magic wands, light-up toys or pinwheels. They may want to hold their favourite toy.

Preschoolers (3 to 5 years) may want to hold a favourite toy or watch toys that light up and make sounds.

School-age children (6 to 12 years) may want to:

• look at items, such as magic wands, light-up toys, video games and picture or “search and find” books
• bring their favourite stuffed animal or toy to hold
• blow bubbles or practise deep breathing while blowing bubbles
• imagine their favourite place
• hear a joke or story or tell you a joke or story

Teenagers (13 to 18 years) can try deep breathing or imagining their favourite place. They also might want to hear a joke or story.

Preparing a child for a blood test depends on the age and experience of the child. Find out more about helping your child cope with tests and treatment.