Understanding Your Blood Tests & Biochemistry
"Blood is that fragile scarlet tree we carry within us". ~Osbert Sitwell
The majority of us at some time have had blood taken, but how many people actually understand:
- Why the blood test is being carried out?
- What the blood test is looking for?
- Understand the results when they come back?
This article will explain, in basic terms, the composition of human blood. The most common blood tests carried out and why doctors, nurses and other professionals need the information tests provide. In addition this will help you to have a better insight in to what blood tests reveal about your health.
Human blood - the basic compilation
The blood has two main components:
- blood cells.
This texture allows substances such as oxygen, carbon dioxide, nutrients, enzymes and other products to be carried to all organs, tissues and cells of the body.
- Plasma is made up of approximately 91-92% water. The other 8% consists of blood plasma proteins and traces of other elements. Not only does the plasma transport blood cells but it also acts as a conductor of heat. Plasma is not a clear liquid but is more straw coloured.
- Within the blood there are three kinds of blood cells - red cells, white cells and platelets.
- Red blood cells, (RBC) account for approximately 99% of all the blood cell categories. The scientific name for a red blood cell is - erythrocyte
- The red colouring comes from haemoglobin. This is a red pigment that carries oxygen in the blood.
- White blood cells, (WBC), fight disease and infections within the body by producing anti-bodies that destroy harmful organisms.
- Platelets form clots when there is injury in order to prevent blood loss from the body. However, if clots develop inside the body for some reason - due to disease for example - then the clots are called a thrombosis and can be dangerous.
Why Are Blood Tests Taken?
There are many reasons why your doctor may want to take a blood test, but some of the most common are listed below:
- To test for or confirm the presence of an infection or virus.
- To test the health of certain organs in the body such as the liver and kidneys. The amount of certain substances found in your blood can tell a doctor whether or not your body organs are in good health.
- To assess your general over all health.
- To check for medication levels in your blood. This is particularly important for very toxic drugs such as digoxin and lithium that can easily build up in the blood causing severe side effects.
- Blood tests can also be used for genetic testing. These look for disorders such as cystic fibrosis.
Lastly, don't be confused by the various bottles with coloured tops that are used. They are only for identification purposes at the laboratory. A specific colour of bottle means that the doctor would like a particular test to be carried out.
The Main Types of Blood Test & What They Mean
Obviously this article can't cover the numerous blood tests available. However, by understanding the most common, it should help to give you a clearer picture of blood tests in general.
In addition, these tests are the names common to the UK. In other countries they may be referred to differently, but the routine tests are used for similar purposes.
Full Blood Count (FBC)
This test is a universal standard when a patient visits a local doctor or is in hospital. This test will give an overall view of your general health. Basically the different types of blood cells that we mentioned earlier - red, white and platelets - will be counted and compared against what should be normal values for the person's age and sex. The FBC can not give a clear cut diagnosis. However, it can give a good indication of problem areas in the body.
An FBC can signal up the following issues:
- If the red cell count is found to be too low then this could be due to anaemia.
- If you have too many red cells within the count then this signifies a potential health problem in a number of areas in the body. For example in respiratory disease. Because the body is not getting enough oxygen into the body due to inflamed lungs, to compensate, the body will produce higher numbers of red cells to try to increase the amount of oxygen into the body. But this is only an example and there are a number of conditions where the red count is increased.
- If the FBC finds that your white cell count is low this could indicate a problem with over all blood cell production in the bone marrow. A low white count could also be an indication of other conditions such as leukaemia.
- If your white cell count is high this is nearly always an indication that the body is responding to some form of infection or virus. What the FBC can't say is where or what that infection is. Further tests such as Blood Culture would be carried out.
- When your platelet count is low this could suggest that a virus is present in the body. Viruses such as Rubella (German measles) are often responsible for a low platelet count. In other cases low platelets can indicate an autoimmune condition such as Lupus. An autoimmune condition is one where the immune system, for some reason, attacks healthy body tissue.
- If your platelet count is found to be higher than normal this can be an indication that an inflammatory condition such as rheumatoid arthritis is present. Another condition that can cause a high platelet count is when the organ of the body called the spleen is damaged. The spleen is responsible for removing damaged or old blood cells from the body.
Electrolytes are essential minerals found in the body. The body cannot function properly without them. An electrolyte test is used to measure their levels in your blood. The important functions that electrolytes carry out are:
- Assist in moving nutrients into cells and removing waste products out of them.
- Helps to maintain a healthy water balance in your body
- Assists in maintaining the levels of acid and alkali in your body
There are three main electrolytes that can be measured with an electrolyte test:
Raised or lowered levels of any of these electrolytes can have a number of possible causes:
- If you have high sodium levels this can be an indication of various conditions such as - dehydration, kidney disease and diarrhoea. *Hypernatremia is the medical term for high sodium levels in the blood.
- When the sodium levels are very low this may indicate some of the following - poorly controlled diabetes, liver disease, a dietary deficiency in sodium and pneumonia. Some types of medication can also cause low sodium levels. This is particularly the case with some anti-convulsants that are used to treat epilepsy. *Hyponatremia is the medical term for low sodium levels in the blood.
- High levels of potassium could be an indication of kidney failure. However there are some medications used to treat high blood pressure that can also cause potassium levels to rise. *Hyperkalaemia is the medical term for raised potassium levels.
- Low levels of potassium are usually the result of excessive sweating or conditions where there are prolonged bouts of vomiting and diarrhoea. *Hypokalaemia is the medical term for low potassium levels.
- High chloride in the blood is usually found with some types of kidney disease. However, raised chloride is also found in excessive diarrhoea and in people who have overactive parathyroid glands. These glands help to regulate the amount of calcium in your body. *Hyperchloremia is the medical term for high levels of chloride in the blood.
- When the chloride levels are very low this is also an indication of various types of kidney disease. But can also be brought on by heavy sweating and vomiting. *Hypochloremia is the medical term for low chloride levels in the blood.
When you visit someone in hospital and they have an intravenous infusion - bags of fluid on a stand, with a tube going into their hand/arm - then frequently these bags of fluid contain electrolytes. Other infusions contain substances such as glucose, anti-biotics and other drugs.
Blood glucose test
Blood glucose tests are used firstly to diagnose diabetes and secondly to monitor the glucose levels in the blood of people who have already been diagnosed with the condition.
Diabetes will occur when either the body cannot produce enough insulin to control glucose levels or when the insulin that is produced does not work effectively. Insulin is a hormone that the body produces to convert glucose into energy.
Blood gas test
A blood gas test is used to check two things:
- firstly how acid or alkaline your blood is
- secondly the balance of both oxygen and carbon dioxide in the blood
Why are these important?
If you have an imbalance in either acid/alkaline or carbon dioxide/oxygen then this could indicate that your lungs are not functioning properly. Secondly, there may be a problem with your ability to breakdown food into energy. This process of breaking down food to release energy is known as metabolism.
An imbalance of oxygen and carbon dioxide can be an indicator of conditions such as pneumonia, COPD - chronic obstructive pulmonary disorder and similar illnesses. Hyperventilation can also cause an imbalance in the blood gases.
Metabolic causes of alkaline-acid imbalances could be caused by conditions such as diabetes, kidney disease or excessive vomiting.
Blood cholesterol test
Although we hear a lot of bad news about cholesterol it is in fact a vital fat required by the body. Problems only arise when there are excessive amounts of cholesterol. This can lead to serious life threatening conditions such as CVD (cardio-vascular system disease) leading to strokes, heart disease/heart attack. The medical term for excess cholesterol in the blood is hyperlipidaemia. Normally this blood test is only carried out if your doctor feels that you may be at risk of having a stroke or developing heart problems.
Liver function test
A liver function blood test is one of the most common tests to be carried out by a doctor. This test helps to check the health of the liver and to diagnose some liver conditions. Disease of the liver can be diagnosed in this way because when damaged or inflamed the liver releases a special enzyme into the blood that can be detected. In addition, the liver produces numerous proteins. When the levels of these proteins in the blood are low this can also indicate that the liver may be diseased.
Liver conditions that can be indicated when this blood test is carried out are:
· Hepatitis - this means an inflammation of the liver.
· Cirrhosis - when the normal structure of the liver is damaged, scar tissue is formed.
- Alcoholic liver disease - basically the liver has been severely damaged by excess alcohol. This condition can also cause other diseases to develop such as hepatitis and cirrhosis.
Test your knowledge
What Does Your Biochemistry Mean?
The bio-chemistry of your blood is the different substances and their levels that the blood usually carries in solution.
If your doctor, nurse or pharmacist shows you your own biochemistry form you may see elements such as the following - this is not exhaustive and only an illustration:
- Hg - haemoglobin
- RCC - red cell count
- WCC - white cell count
- eGFR - estimated Glomerular Function Test or creatinine clearance test - is a number given based on your blood test for creatinine. This shows how well your kidneys are working.
- Creatinine - this is a nitrogenous organic acid found in most animals and this substance helps to supply energy to the body cells. It is normally excreted by the kidneys. Therefore, if levels in the blood are high, this could be an indication that the kidneys are not working properly.
- CorCal - corrected calcium. This is the result of how much calcium is in the blood. The amount is usually corrected to allow for the amount of calcium that binds to albumin in the body. High or low levels of calcium in the blood can indicate various diseases and conditions.
- Albumin - is a protein made by the liver. It helps to regulate the osmotic pressure in the blood. A low albumin level is an indicator not only of malnutrition but many other conditions and diseases such as liver disease and inflammation.
- Na - sodium
- K - potassium
- po4 - phosphorus. This is a vital mineral required by the body for both healthy new growth of bone and for normal functioning of all cells in the body. Depending on whether the levels of po4 are high or low is an indication of problems in the body. For example, high levels could indicate kidney disease. Whereas low levels might be an indication of sepsis.
- Urea - is a waste product formed during the breakdown of proteins in the body. It is sometimes called urea nitrogen. Like creatinine it is usually excreted in the urine by the kidneys. High levels of urea can indicate that the kidneys are not working properly. However it’s usually the creatinine levels that are preferred for estimating proper kidney function.
- Bilirubin - is a yellow coloured substance that results from the natural breakdown of haemoglobin. This yellow pigment gives urine its familiar colour. It’s also responsible for the yellowish tinge around bruises and the yellow skin colour in people who have jaundice. High levels of bilirubin in the blood can be an indication of liver disease.
This explanation is a simplified one and your doctor may well ask a laboratory to test other body substances not listed here. But those above are among the most common.
I hope this article has been helpful in giving you more information about why blood tests are needed and what health professionals are looking for in your blood. However, as always, this article is not intended to replace the advice of your doctor. If you have any concerns about your health speak to them as soon as you can.
©Seeker7(Helen Murphy Howell) August 5th 2013
© 2011 Helen Murphy Howell