Blood tests can be used in a number of ways:
such as helping to diagnose a condition, assessing the health of certain organs or screening for some genetic conditions.
Some of the common blood tests include:
- blood culture
- blood glucose (blood sugar) tests
- blood typing
- cancer blood tests
- chromosome testing (karyotyping)
- coagulation tests and international normalised ratio (INR)
- C-reactive protein (CRP) test
- electrolyte test
- erythrocyte sedimentation rate (ESR)
- full blood count (FBC)
- genetic testing and screening
- liver function test
- thyroid function test
- hormone tests
Blood cholesterol test
Cholesterol is a fatty substance mostly created by the liver from the fatty foods in your diet and is vital for the normal functioning of the body.
Having a high level of cholesterol can contribute to an increased risk of serious problems such as heart attacks and strokes.
Blood cholesterol levels can be measured with a simple blood test. You may be asked not to eat for 12 hours before the test (which usually includes when you’re asleep) to ensure that all food is completely digested and won’t affect the result, although this isn’t always necessary.
This involves taking a small sample of blood from a vein in your arm and from one or more other parts of your body.
The samples are combined with nutrients designed to encourage the growth of bacteria. This can help show whether any bacteria are present in your blood.
Two or more samples are usually needed.
Cancer blood tests
A number of blood tests can be carried out to help diagnose certain cancers or check if you’re at an increased risk of developing a particular type of cancer.
These include tests for:
- prostate-specific antigen (PSA) – this can help diagnose prostate cancer, although it can also detect other problems such as an enlarged prostate or prostatitis
- CA125 protein – a protein called CA125 can indicate ovarian cancer, although it can also be a sign of other things such as pregnancy or pelvic inflammatory disease (PID)
- BRCA1 and BRCA2 genes – certain versions of these genes can greatly increase a woman’s chance of developing breast cancer and ovarian cancer; this test may be carried out if these types of cancer run in your family
Chromosome testing (karyotyping)
This is a test to examine bundles of genetic material called chromosomes.
By counting the chromosomes (each cell should have 23 pairs) and checking their shape, it may be possible to detect genetic abnormalities.
Chromosome testing can be used:
- to help diagnose disorders of sex development (DSDs), such as androgen insensitivity syndrome
- for couples who have experienced repeated miscarriages, to see if a chromosomal problem could be responsible
A coagulation test may be used to see if your blood clots in the normal way.
If it takes a long time for your blood to clot, it may be a sign of a bleeding disorder such as haemophilia or von Willebrand disease.
A type of coagulation test called the international normalised ratio (INR) is used to monitor the dose of anticoagulants, such as warfarin, and check that your dose is correct. Read more about monitoring your anticoagulant dose.
reactive protein (CRP) test
This is another test used to help diagnose conditions that cause inflammation.
CRP is produced by the liver and if there is a higher concentration of CRP than usual, it’s a sign of inflammation in your body.
Electrolytes are minerals found in the body, including sodium, potassium and chloride, that perform jobs such as maintaining a healthy water balance in your body.
Changes in the level of electrolytes can have various possible causes, including dehydration, diabetes or certain medications.
Erythrocyte sedimentation rate (ESR)
This test works by measuring how long it takes for red blood cells to fall to the bottom of a test tube. The quicker they fall, the more likely it is there are high levels of inflammation.
An ESR is often used to help diagnose conditions associated with inflammation, such as:
- Crohn’s disease
- giant cell arteritis
- polymyalgia rheumatica
Along with other tests, an ESR can also be useful in confirming whether you have an infection.
Full blood count (FBC)
This is a test to check the types and numbers of cells in your blood, including red blood cells, white blood cells and platelets.
This can help give an indication of your general health, as well as provide important clues about certain health problems you may have.
For example, an FBC may detect signs of:
- iron deficiency anaemia or vitamin B12 deficiency anaemia
- infection or inflammation
- bleeding or clotting disorders
Genetic testing and screening
This involves extracting a sample of DNA from your blood, then searching the sample for a specific genetic change (mutation).
Genetic conditions that can be diagnosed this way include:
- haemophilia – a condition that affects the blood’s ability to clot
- cystic fibrosis – a condition that causes a build-up of sticky mucus in the lungs
- spinal muscular atrophy – a condition involving muscle weakness and progressive loss of movement
- sickle cell anaemia – a condition that causes a shortage of normal red blood cells
- polycystic kidney disease – a condition that causes fluid-filled sacs called cysts to develop in the kidneys
Genetic screening can also be used to check if someone carries a particular gene that increases their risk of developing a genetic condition.
For example, if your brother or sister developed a genetic condition in later life, such as Huntington’s disease, you may want to find out whether there is a risk that you could also develop the condition.
Liver function test
When the liver is damaged, it releases substances called enzymes into the blood and levels of proteins produced by the liver begin to drop.
By measuring the levels of these enzymes and proteins, it’s possible to build up a picture of how well the liver is functioning.
This can help to diagnose certain liver conditions, including hepatitis, cirrhosis (liver scarring), and alcohol-related liver disease.
Thyroid function test
This test is used to test your blood for levels of thyroid-stimulating hormone (TSH), and, where needed, thyroxine and triiodothyronine (thyroid hormones).
If you have low or high levels of these hormones, it could mean you have a thyroid condition such as an underactive thyroid or overactive thyroid.