HCT (haemocrit) measures the amount of space (volume) red blood cells take up in the blood.

Raised levels can result from pregnancy, living at altitude, dehydration as well as low availability of oxygen through chronic lung disease and even sleep apnoea.

Low levels indicate anaemia.

Red blood cell (RBC) count analyses the number of red cells in the blood. Red blood cells carry oxygen from the lungs to the rest of the body. They also carry carbon dioxide back to the lungs so that it can be exhaled. 

A high count (thicker blood) means there is a chance that the red blood cells will clump together and block tiny blood vessels. This also makes it difficult for your red blood cells to carry oxygen.

A low count (anaemia) means that your body may not be getting the oxygen it needs and can be caused by nutritional deficiency (lack of iron, folic acid, vitamin B12), over-hydration as well as bleeding and bone marrow disorders. 

MCV (mean corpuscular volume) reflects the size of your red blood cells. 

A high result may indicate a vitamin deficiency of folate or vitamin B12 and is often seen in excessive alcohol consumption associated with liver inflammation. 

A low result indicates anaemia, often caused by iron deficiency.

MCH (mean corpuscular haemoglobin) is the average amount of haemoglobin contained in your red blood cells. 

Together with MCV and MCHC, MCH results can help in the diagnosis of different types of anaemia. 

MCHC (mean corpuscular haemoglobin concentration) is the average concentration of haemoglobin in your red blood cells.

A high level can indicate the presence of spherocytes (a type of red bood cell with too much haemoglobin) or a deficiency of folic acid or vitamin B12 in the diet.

A low level can indicate chronic blood loss or iron deficiency.

RDW (red cell distribution width) shows whether the cells are all the same size or different sizes or shapes. Normally cells are fairly uniform, although a raised RDW result (indicating greater variaton in cell size and shape than is normally seen) can be caused by deficiency in iron, vitamin B12 or folic acid. 

White blood cells are key to your body's immune or defence system. They fight infections and protect your body from foreign invaders such as harmful germs and bacteria. 

A raised white blood cell (WBC) count can indicate recent infection, inflammation, trauma and even stress. Your WBC can also be raised when taking certain medications.

A decreased WBC can result from a vitamin deficiency such as folate or vitamin B12, as well as liver disease and diseases of the immune system. 

Neutrophils are a type of white blood cell that are responsible for helping your body fight infection. When neutrophils are low you can be more vulnerable to illness and infection.

Neutrophils can be raised after severe stress on the body from a bacterial infection, recent exercise or sudden kidney failure. 

Low neutrophils can be casued by a deficiency in vitamin B12 or folic acid, severe bacterial infection and some autoimmune diseases. 

Lymphocytes are a type of white blood cell which fight bacterial and viral infections. They include T cells, B cells and natural killer cells. 

Lymphocytes can be elevated for many reasons but it is common for them to be raised after recent infection, particularly after the flu. They can also be raised due to autoimmune disorders and some cancers. 

The most common cause for lymphocytes to be depleted is the common cold. 

Monocytes are a type of white blood cell that engulf and remove pathogens and dead or damaged cells from our blood. The heat and swelling of inflammation is caused by the activities of these cells. 

Elevated monocytes can indicate chronic inflammatory disease, chronic infection, parasitic infection and Cushings disease. 

Low levels can be due to autoimmune disorders such as lupus and rheumatoid arthiritis as well as drugs which affect the bone marrow such as those used in chemotherapy. 

Eosinophils are a type of white blood  cell whose function is to remove parasitic infections as well as to regulate inflammation to mark an infected site. 

Levels of eosinophils can be elevated if the scale of inflammation is greater than necessary to control the damage (as is the case in asthma and allergic responses) as well as in parasitic and fungal infections, autoimmune diseases and skin disorders. 

Low levels of eosinophils are not usually cause for concern and can be caused by the administration of steroids. 

Basophils are a type of white blood cell that protect your body from bacteria and parasites such as ticks.

An elevated basophil count can be due to inflammatory conditions such as Crohn's disease, ulcerative colitis and dermatitis, recent infection and hormone imbalance (e.g. hypothyroidism).

A low basophil count can be caused by pregnancy, stress and use of steroids.

A blood film report is an examination of the shape, size and number of blood cells under the microscope. Oxygen is carried less effectively by red blood cells if they are of abnormal size or shape, and this can result in anaemia. Too many or too few white blood cells can signify a blood disorder and can affect your body's ability to fight infection. 

Platelets or clotting cells are the smallest type of blood cell and are important in blood clotting. When bleeding occurs, the platelets swell, clump together and form a sticky plug (a clot) which helps stop the bleeding. 

If platelet levels are raised there is an increased risk of blood clots forming in blood vessels.

If platelet levels are too low there is a risk of easy bruising and uncontrolled bleeding. 

MPV (mean platelet volume) is a measurement of the average size of your platelets. New platelets are larger than older ones and a raised MPV result occurs when increased numbers of platelets are being produced. MPV provides an indication of platelet production in your bone marrow. 

C-Reactive Protein (CRP) is an inflammation marker used to assess whether there is inflammation in the body - it does not identify where the inflammation is located. High Sensitivity CRP (CRP-hs) is a test which is used to detect low-level inflammation which is thought to damage blood vessels which can lead to a heart attack or stroke. 

Raised levels are a risk factor for cardio-vascular disease. 

Sodium is both an electrolyte and a mineral. It helps regulate the water and electrolyte balance of the body and is important in the operation of nerves and muscles. Sodium levels in the blood are regulated by the kidneys. 

Excess sodium in the blood is often due to dehydration but can also indicate that the kidneys are not working properly. 

Too little sodium is often caused by fluid retention (oedema) or reflects loss due to vomiting, diarrhoea or excessive sweating. 

Urea is waste product produced as the body digests protein and is carried by the blood to the kidneys, which filter the urea out of the blood and into the urine. The urea test examines how well the kidneys are functioning.

Raised levels of urea in the blood can be caused by dehydration or high protein consumption or may indicate that the kidneys are not working properly. 

Low amounts of urea in the blood may indicate a low protein diet, excess hydration, malnutrition or liver failure. 

Creatinine is a chemical waste molecule that is generated from muscle metabolism. Measurement of this is an indicator of the levels of other waste products in the body. Creatinine is an accurate marker of kidney function.

Elevated creatinine can be caused by high intake of animal protein, taking creatine supplements and vigorous exercise but can also indicate that the kidneys are not working properly.

Low creatinine can be caused by a low protein diet, reduced muscle mass or sometime that the kidneys are simply functioning efficiently.

Alkaline phosphatase (ALP) is an enzyme found mainly in the liver and bones. Raised levels can indicate bone or liver disease. Elevated ALP is assessed in conjunction with other liver function tests to determine whether the problem lies in the liver or the bones.

Pregnancy can also cause raised ALP and it is often elevated in growing teenagers.

Aspartate transferase (AST) is an enzyme created mainly by the cells of the liver and the heart. Any injury to the heart or liver, and other bodily tissues, will cause AST to be released into the bloodstream. Levels can be raised following a heart attack or from liver damage caused by alcohol, drugs or viruses (hepatitis).

AST can also be elevated after vigorous exercise.

Alanine transferase (ALT) is an enzyme which is produced by the liver and can indicate liver damage caused by alcohol, drugs or viruses (hepatitis). Small amounts of ALT are normal, but raised levels may indicate that your liver is inflamed.

Elevated levels of ALT can also be caused by recent vigorous exercise.

CK (creatine kinase) is a muscle enzyme which signifies muscle cell damage and death. CK levels tend to be higher in people with greater muscle mass.

The level of CK in the blood is measured to assess muscle damage - it can rise rapidly after muscle trauma, but will subside as the damage repairs. If CK continues to rise it indicates that muscle damage is not being repaired. If you have been to the gym the day before your blood test you may well exhibit raised levels of CK.

Gamma GT is a liver enzyme which is raised in liver and bile duct diseases. It is used in conjunction with ALP to distinguish between bone or liver disease. Gamma GT is also used to diagnose alcohol abuse as it is raised in 75% of long term drinkers.

Bilirubin is a product of haemoglobin breakdown. It is removed from the body via the liver, stored and concentrated in the gall bladder and excreted into the bowel. Elevated levels can cause the skin and whites of eyes to become yellow (jaundice) as the liver is unable to remove enough bilirubin from the blood. This can indicate liver damage.

Bilirubin can also be raised due to a blocked bile duct as well as Gilbert's Syndrome.

Total Protein represents the sum of albumin and globulin. Abnormal levels can indicate malnutrition as well as a liver or kidney disorder. 

Albumin is made mainly in the liver and helps to keep the blood from leaking out of blood vessels. It also helps carry some medicines and other substances through the blood and is important for tissue growth and healing.

Low albumin levels can indicate liver disease and can also be a marker for chronic ill-health, malnutrition and inflammation. It can also occur in kidney conditions such as nephrotic syndrome and diabetes.

Raised levels are usually caused by dehydration.

Globulin consists of different proteins and is made by the liver and the immune system. Certain globulins bind with haemoglobin while others transport metals, such as iron, in the blood and help fight infection.

Calcium is the most common mineral in the body and one of the most important. The body needs it to build and repair bones and teeth, help nerves and muscles to function, blood to clot and also help the heart to work. Vitamin D is essential to absorb calcium.

The majority of calcium in the body is stored in bone, the rest is found in the blood. If the calcium result is abnormal, a corrected calcium calculation is carried out to aid further investigation.

Around half of the total calcium in your blood is bound by albumin. Corrected calcium estimates your calcium level assuming albumin is a specified normal value. 

Uric acid is a waste product from the digestion of protein. High levels can lead to excess uric acid being deposited as crystals in the tissues of the body. When this occurs in joints it causes the painful condition known as gout. 

Uric acid levels are best tested 6 weeks after symptoms appear as they may not be raised at the onset of a gout attack.

HbA1c or Haemoglobin A1c is also known as glycosolated haemoglobin and is a longer term measure of glucose levels in your blood than a simple blood glucose test. Glucose attaches itself to the haemoglobin in your red blood cells, and as your cells live for around 8-12 weeks it provides a good indication of the level of sugar in your blood over a 2-3 month period.

This is an important measure for diagnosing type 2 diabetes as well as understanding how well blood sugar levels are being contolled in people who have already been diagnosed with diabetes.

This test measures how much iron is in your blood with the aim of identifying iron deficiency anaemia or iron overload syndrome (haemochromatosis)

The symptoms of too much or too little iron can be similar - fatigue, muscle weakness, moodiness and difficulty concentrating.

A raised result can mean that you have iron overload syndrome, an inherited condition where your body stores too much iron, or that you are over-supplementing or that you have a liver condition.

A low result can mean that you are anaemic or are suffering from gastro-intestinal blood loss (or other blood loss). Anaemia is also very common in pregnant women.

Total iron binding capacity (TIBC) is a measure of the amount of iron that can be carried through the blood. 

A raised TIBC result usually indicates iron deficiency whereas low TIBC can occur with iron overload syndrome (haemochromatosis).

Transferrin is made in the liver and is the major protein in the blood which binds to iron and transports it through the body.

Low levels of transferrin indicate iron deficiency while high levels indicate iron overload.

Triglycerides are a type of fat (lipid) that circulate in the blood. After you eat, the body converts excess calories into triglycerides which are then transported to cells to be stored as fat. Your body releases triglycerides to be used for energy. 

Raised triglycerides are thought to be a risk factor for peripheral vascular disease (affecting the blood vessels which supply your arms and legs as well as organs below the stomach) as well as microvascular disease, affecting the tiny blood vessels around the heart. 

Cholesterol is an essential body fat (lipid). It is necessary for building cell membranes and for producing a number of essential hormones. Cholesterol is manufactured in the liver and also comes from the food we eat. Elevated cholesterol is a risk factor for heart disease - the recommended level is below 5 mmol/L.

Cholesterol however is made up of both good (HDL) and bad (LDL) cholesterol so it is important to investigate a raised total cholesterol result to determine the cause. High levels of HDL cholesterol can cause a raised total cholesterol result but may actually be protective against heart disease.

HDL cholesterol (high density lipoprotein) removes cholesterol from the bloodstream and transports it to the liver where it is broken down and removed from the body in bile. HDL cholesterol is commonly known as "good cholesterol". 

Raised levels are believed to be protective against heart disease, while low levels are associated with increased risk of a heart attack.

LDL cholesterol (low density lipoprotein) carries cholesterol, triglycerides and other fats to various tissues throughout the body. Too much LDL cholesterol, commonly called "bad cholesterol", can cause fatty deposits to accumulate on artery walls, potentially leading to artherosclerosis and heart disease. 

Non-HDL cholesterol is calculated by subtracting your HDL cholesterol result from your total cholesterol. It therefore includes all the non-protective and potentially harmful cholesterol in your blood, not just the LDL cholesterol. As such, it is considered to be a better marker for cardiovascular risk than total cholesterol and LDL cholesterol. The recommended level of non-HDL cholesterol is below 4 mmol/L.

HDL % of total cholesterol is considered to be more indicative of your risk of cardiovascular disease than total cholesterol alone. 

A result below 20% indicates an increased risk of cardiovascular disease, while one above 20% indicates a lower than average risk.