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Blood testing glossary

Are blood testing terms leaving you feeling confused? We explain blood test-related terms in a way that makes sense.

ABO system

The ABO system categorises the four basic types of human blood: A, AB, B, and O.


A basophil is a type of white blood cell. Basophils appear in many specific kinds of inflammatory reactions, particularly those that cause allergic symptoms.


Biochemistry is the study of the chemical processes going on inside living things. A biochemistry profile is a series of blood tests that measure the functional capacity of several critical organs and body systems, including the liver and kidneys.


A biomarker is a combination of the words biological and marker. It can refer to many different substances in the body:  hormones, minerals, or disease status, for example. Biomarkers can be objectively measured and are indicators of how the body is functioning.

Blood donor

A blood donor is a person who gives blood for use in a blood transfusion.

Blood test

A blood test is a scientific examination of a sample of blood. A blood test is typically used to investigate a health concern, diagnose or monitor a condition, or inform healthy lifestyle choices.

Blood transfusion

A blood transfusion is a process of transferring blood from a healthy person, into a patient, via a needle.

Blood vessels

Blood vessels carry blood through the tissues and organs. Veins, arteries, and capillaries are all types of blood vessels.

Carbon dioxide

Carbon dioxide is a colourless gas that naturally sits in the air but is also produced as a waste product of respiration, which is how the body releases energy.


Endocrinology is a branch of biology and medicine that looks after the endocrine system, its diseases, and hormones.


Eosinophils is a type of white blood cell that helps fight certain infections. They can be raised during allergic reactions, inflammation, and parasitic infections.

External Quality Assessment (EQA)

EQA is the process of challenging the effectiveness of a laboratory’s quality management system.


Haematology is the branch of medicine that involves the study and treatment of the blood.


Immunology is the branch of medicine that involves the study of immunity and the immune system.

Internal Quality Control (IQC)

IQC is a set of procedures that are put in place to continuously assess laboratory work and the results.


A lymphocyte is a type of white blood cell that is part of the immune system and helps fight disease and infections. Lymphocytes include B cells, which produce antibodies, T cells, and natural killer cells.


Microbiology is the study of microorganisms, including bacteria, viruses, and fungi.


Monocytes are the largest type of white blood cell. They can transform into macrophages, which ingest microorganisms, and dendritic cells, which locate bacteria and viruses in the body and present them to other white blood cells.


Neutrophils are white blood cells that make up 40% to 70% of all white blood cells in humans. Neutrophils represent the first line of defence in response to invading microbes by engulfing pathogens or releasing antimicrobial chemicals contained in specialised granules.


Oxygen is a colourless gas found in the air. It is needed for respiration (the body’s way of releasing energy) and diffuses from the lungs into the bloodstream where it is carried to the organs.


Pathology is the study of the causes and effects of diseases, specifically the branch of medicine that deals with examining samples in a laboratory for diagnostic (or forensic) purposes.


Plasma is the colourless liquid portion of blood that holds blood cells.


Platelets (thrombocytes) are colourless blood cells that help blood clot by clumping and forming plugs when blood vessels are injured.

Red blood cells

Red blood cells are the most common type of blood cell. Their primary function is to carry oxygen to the cells and tissues of the body and return carbon dioxide, a waste product, to the lungs.

Rhesus system

The Rhesus system is a blood group system that specifies whether your blood type is negative or positive (Rh D positive or negative). This is determined by whether there is a specific protein (antigen) on the surface of a red blood cell.

White blood cells

White blood cells are part of the immune system. They help the body fight infection and other diseases.

United Kingdom Accreditation Service (UKAS)

The United Kingdom Accreditation Service (UKAS) is a national accreditation body that assesses the competence of organisations that provide certification, testing, inspection, and calibration services.

Uric acid

Uric acid is a waste product found in the blood. A raised level increases the risk of developing gout.


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