What are we looking for in Blood Tests?
Why do we do them?
Blood tests help doctors to come to the correct diagnosis, and complement the ‘history’ and clinical examination that your doctor will undertake with you. Blood contains a variety of cells and proteins that circulate around the body. These can change when you become unwell and helps doctors to form an opinion about your diagnosis. Some markers may be very specific to a particular disease, whilst others may be more general to help guide further investigation. Blood tests can be used to monitor your response to treatment, and also to ensure that any possible allergic response or toxicity from your medication is picked up early on and dealt with appropriately.
How are they done?
There is usually nothing special that you need to do to prepare for a blood test. The doctor or nurse will clean the skin where the blood is to be drawn, usually with an alcohol-based solution; to prevent bacteria getting into the puncture site and causing infection. Next, they will look for a suitable vein to take blood from, by visually examining your arm, and then by feeling it. Once the vein has been located, the doctor or nurse will apply a tourniquet, which is like an elastic band, to your arm, which causes the vein to swell. A needle with an attached syringe will be inserted through the skin, and once it is inside the vein, the syringe will be drawn back to fill the tube with blood. You will feel a scratch as the needle is inserted, but this lasts just a second. Multiple tubes may be required, depending on how many tests you require, but these can all be taken with a single needle.
Once all the necessary samples have been taken, the needle is removed, and a small plaster can be applied. The doctor will then send the sample off for laboratory analysis.
How are the results interpreted?
Some test results are available within 24 hours but some others will take longer. If the sample needs to be sent to another hospital it may take a few weeks to get the result. They will be sent back to your doctor who will review the results and may write to your GP and yourself. The doctor can use these results to help make a diagnosis. This will help them to plan future treatment and or to see if the current treatments are working to bring your condition under better control.
What blood tests might be done?
Here are some of the tests routinely performed by the Rheumatology Department, including why they are performed and what they may show.
It is important to note that your doctor will only perform tests which they consider appropriate to your individual case. If you are unsure what blood tests have been done, you can speak to your doctor and they will be more than happy to share this information with you.
Antibodies are proteins made by the immune system of your body. They help to fight off an infection. An auto-antibody is also a type of protein, which can bind to your own tissues and organs. They are usually produced in error and can help doctors to understand what is causing your symptoms.
Here are some of the main antibodies tested for in the Rheumatology department, as well as what those antibodies bind to (ie are specific for):
Anti-nuclear antibodies (ANA):
This is likely to be the first antibody test that the doctor will order if they suspect that you have an autoimmune condition such as SLE. If you are negative for ANA test it is much less likely that you will have an autoimmune disease. These antibodies bind to proteins in the cell especially the nucleus, which houses your DNA. The laboratory will measure the amount of antibody in your blood sample (called the titre). They will also report on how the antibody stains up the cell (eg homogenous, speckled, nucleolar and centromere). Both results can help the doctor to come to the correct diagnosis. It’s important to be aware that many perfectly healthy people also make ANA. If your GP discovers that you have the ANA antibody in high enough concentrations, they will ask for details of any symptoms you have (called a history), asking you specific questions to ascertain if you could have a connective tissue disease (CTD). If you do not have symptoms of a CTD and your blood tests are otherwise normal, they will reassure you and no further investigations are necessary.
Our bodies are made up to billions of tiny cells. Most of these cells have a structure within them called the nucleus. Some patients with a rheumatic condition produce antibodies, that can bind to the nucleus, called anti-nuclear antibodies (ANA). They are also produced by some healthy people so your doctor will need to take a detailed history before deciding they are associated with your symptoms.
These are a type of anti-nuclear antibody (ANA), which bind to DNA or proteins associated with DNA. They are used to help a doctor make a diagnosis of systemic lupus erythematosus (SLE), also known as lupus.
If your doctor finds that you do have a positive ANA and a relevant clinical history, they will consider asking for more specific tests. As an example these include the ENA (which stands for extractable nuclear antigens) panel and other more specific tests. This is a panel of antibodies that help doctors to understand if you have an autoimmune disease such as SLE, Sjogren’s syndrome, mixed connective tissue disease, myositis or scleroderma.
They include the following:
- Anti-Ro antibodies
- Anti-La antibodies
- Anti-Sm antibodies
- Anti-RNP antibodies
- Anti-Jo-1 antibodies
- Anti-centromere antibodies
- Anti-Scl-70 antibodies
Anti-Ro antibodies (anti-SSA antibodies):
These are a type of anti-nuclear antibody (ANA) that can bind to RNA associated proteins. They are most often associated with Sjögren’s syndrome. It is associated with Sjögren’s syndrome. Patients with systemic lupus erythematosus (SLE) also sometimes have this antibody if they have developed secondary Sjögren’s syndrome.
Anti-La antibodies (anti-SSB antibodies):
They are often associated with Sjögren’s syndrome.
Found in 30-60% of patients with Sjögren’s syndrome (usually with anti-Ro antibodies).
Found in 15% of patients with diffuse scleroderma (usually with anti-Ro antibodies).
Sometimes found in SLE, though usually only when Sjögren’s syndrome is also present.
Anti-Sm antibodies (anti-Smith):
They are found in 5-30% of patients with systemic lupus erythematosus (SLE), where it is very specific.
These antibodies bind to small RNA/protein complexes, (called snRNPs) in the cell nucleus; the structure which houses your DNA. They are commonly found in patients with mixed connective tissue disease. Here patients develop a combination of different rheumatic diseases including SLE, scleroderma and polymyositis.
Many different components are needed to make new proteins within your cell. One if these is an enzyme called histidyl-tRNA synthetase, which speeds up (catalyses) one part of the process. Anti-Jo-1 antibodies bind to this enzyme. Your doctor may test you for this if you have symptoms that include weak muscles (myositis), skin rash shortness of breath or cold white fingers (Raynauds). They are strongly associated with a condition called polymyositis.
These are a type of anti-nuclear antibody (ANA), which binds to nuclear proteins. It is seen in some autoimmune conditions, particularly systemic sclerosis, which can be generalised or localised (CREST syndrome).
Found in 60% of patients with limited systemic scleroderma.
Found in 15% of patients with diffuse scleroderma.
This is another antibody that can bind to an enzyme (called topoisomerase I). This enzyme acts to relax DNA within the nucleus of the cell, which is needed to allow the DNA to be read (or transcribed). They are seen in 34-40% of patients with scleroderma.
These antibodies bind to an enzyme that is needed inside your cells to make new proteins. Your doctor may want to test you for this if you have weak muscles and a rash (that resembles a shawl over your shoulders) or around your eyes or fingers. These symptoms are seen in patients with dermatomyositis.
These antibodies bind to proteins that are attached to fat particles (phospholipids). This makes the blood more likely to clot. These antibodies are associated with the antiphospholipid syndrome and systemic lupus erythematosus (SLE).
Anti-cardiolipin antibody is a type of anti-phospholipid antibody targeting a substance called cardiolipin. This antibody is mostly seen in patients with the anti-phospholipid syndrome, but it can also be seen in patients who have SLE. However, people can have these antibodies and still be well. Your doctor may want to review you from time to time to ensure that you are not developing any problems secondary to these antibodies being present.
Rheumatoid Factor (RF)
Rheumatoid factor is an antibody, that is made when you have chronic infections or inflammation. Its role is to bind to other antibodies. It is commonly seen in individuals with rheumatoid arthritis (RA). However, it is quite non-specific and can be seen in other inflammatory diseases as well as the aging population.
Antibodies that bind to citrullinated proteins are very specific for rheumatoid arthritis (RA) and are routinely used to help doctors make this diagnosis. They may be present for many years before a patient develops rheumatoid arthritis and can also be more commonly seen in relatives of family members who have RA.
Other blood tests that help in the diagnosis or monitoring of rheumatic conditions
C-reactive Protein (CRP)
C-reactive Protein is produced by the liver in response to inflammation or infection in your body. Many rheumatic conditions cause the level of CRP to increase. It is a good way for the doctor to monitor if you have ongoing inflammation or infection.
Erythrocyte Sedimentation Rate (ESR)
Erythrocyte Sedimentation Rate is used to test for inflammation in the body, by looking at how quickly your red blood cells fall to the bottom of a special test tube. If your red blood cells fall faster, it means you are more likely to have some inflammation in your body. However, the test is quite non-specific and the doctor will want to look at the ESR in the context of your clinical history and examination.
Full Blood Count (FBC)
The laboratory checks the number of red blood cells, white blood cells and platelets in your blood. Red blood cells carry oxygen round the body, whilst white blood cells are important in fighting infection. Platelets are important for plugging wounds, which helps to stop bleeding.
A Full Blood Count is a very common blood test used to check your general health, as well as screen for certain conditions, such as anaemia, infection or bleeding and clotting disorders.
Liver Function Tests (LFTs)
The liver is an important organ for detoxifying or ‘cleaning’ the blood. When the liver becomes damaged, it releases certain markers into the blood which we can measure to determine the extent and nature of the damage. Liver damage can result from drug toxicity, too much alcohol or from a number of conditions that inflame or damage the liver.
Liver damage can result from drug toxicity, inflammation or other causes that directly target the liver cells (such as excessive alcohol consumption).
Urea & Electrolytes (U&Es)
This is a very common test which used to check your general health, as well as your kidney function.
Urea is a waste product made in the body which is removed by the kidneys and passed out in the urine. High levels of urea may suggest that your kidneys are not doing a good enough job at filtering your blood, and could be a marker of kidney disease.
Electrolytes are minerals found inside your body, such as sodium, potassium, calcium and chloride. These have many important functions in controlling your water balance and blood pressure, muscle contraction, nerve signalling, and many others. Changes in the amounts of electrolytes in your blood usually indicates a problem, and by looking at each individual electrolyte and whether it’s high or low, your doctor can determine what that problem might be. Electrolyte levels are also controlled by the kidneys, and certain changes in their levels may indicate kidney disease. Dehydration, drugs and diabetes may also affect your electrolytes.
Uric acid is a waste product formed from the breakdown of various foods such as liver, beer, wine, anchovies, mackerel and dried beans, as well as from normal cell breakdown in the body. High levels of uric acid are associated with gout. However, you can have a high level of uric acid in the blood and not have gout. In addition, you can have a normal level of uric acid in the middle of a gout attack. Hence the doctor will look at the level of uric acid in conjunction with your overall clinical history.