A blood test is any laboratory test of blood to analyze its contents or to establish the blood group. Blood testing devices range from batch analysis systems to this on-the-spot test of red blood cells used in the diagnosis of anemia.
Why are blood tests carried out?
Blood tests are usually conducted to establish the presence of disease. This may be apparent in the blood cells, the plasma or any of their constituents.
Red blood cells (erythrocytes) are responsible for transporting oxygen around the body, white cells (leukocytes) are an important part of the body’s defense system against disease, and small cell fragments called platelets are active clotting agents.
Plasma is the liquid part of blood and consists of water with some dissolved substances. An imbalance of any of the three types of blood cells or constituents of plasma may indicate an underlying disease.
Blood tests can also be used to determine blood group. Classification systems identify the presence or absence of specific antigens on the surface of the red blood cells, the ABO system being the most important.
Blood group determination is vital before a transfusion because the use of blood from the wrong group can cause a severe reaction, or may even prove to be fatal.
This test is performed on all women during pregnancy, as those who are rhesus negative may produce their harmful antibodies against the fetal blood in future pregnancies.
Specific antibodies are given by injection to prevent this. Blood tests are also carried out to monitor treatment, establish paternity, and to see if a person is carrying an inherited faulty gene which may be passed on to children. For example, the gene that causes cystic fibrosis.
What are the main types of blood test?
Full blood count: This is the most common form of blood test, being a mechanical count of the number of red cells, white cells, and platelets in a small sample of blood. The results are then expressed regarding the proportion of. The total made up of each type of cell.
The full blood count is usually carried out to see whether a person has anemia. A shortage of certain blood cells can indicate, for example, a bone marrow malfunction.
Blood smear: This test examines the shape, appearance and relative numbers of different types of white blood cells and is usually carried out at the same time as a full blood count.
It consists of a few drops of blood spread on a slide for microscopic examination. The sample is then colored with dyes to make the cells more visible. Abnormal cells may reveal conditions such as glandular fever (infectious mononucleosis).
Blood chemistry tests: These can measure some substances in the blood giving valuable in-formation about the function of organs such as the kidneys, liver and endocrine glands.
Blood gas tests: Here, arterial blood is usually used to determine the acid-alkaline balance and the levels of oxygen, carbon dioxide and bicarbonate. The results may help in the
Microbiological tests: These look for infections in the bloodstream by making a culture of bacteria found in test samples.
Self-tests: Diabetics regularly have to test their blood by pricking a fingertip and then squeezing out a drop onto a strip of special paper.
This changes color according to the sugar content of the blood and shows whether the particular diet or insulin treatment they are using is keeping their blood sugar within normal limits. A full test to measure the amount of sugar in the blood is performed if diabetes is only suspected.
Where do blood tests help most?
Where there is a high level of a protein called the rheumatoid factor in the blood; through glandular fever, hepatitis, and malaria; to inherited diseases such as a disorder of the red blood cells called sickle cell anemia and the bleeding disease, hemophilia.
Blood tests can also measure the amount of fat, particularly cholesterol, circulating in the bloodstream. High cholesterol levels mean an increased risk of heart disease.
Those affected will usually be advised to switch to a low-fat diet and,
Finally, the absence of antibodies in the blood to certain diseases such as German measles and measles shows that a person is not immune to them, either because they have not been vaccinated or be-cause they have never had the disease in childhood.
How is a blood test taken?
Samples are made by drawing out about 10m1 of blood with a sterile
How long will I wait for the results?
Test equipment is often automated and computerized so that hundreds of samples can be tested simultaneously for the levels of dozens of substances, in a matter of minutes.
The results of most routine tests will go back on the same day to the health-care professional requesting them. More specific tests, such as gene analysis to check for abnormalities, can require procedures which take over a month.