This booklet will help you understand the various tests which are used to assess your arthritis. It explains why tests are performed and what the most common tests involve.
It may not answer all your questions because there are so many different investigations and so many different types of rheumatic diseases. If you have further questions after reading this booklet, please ask your doctor or other medical staff.
Why perform tests?
Tests (or investigations) are often used for people with arthritis. They are used for one or more of the following reasons:
- To make a diagnosis
- To rule out other explanations for your illness
- To assess how active your arthritis is
- To predict how your arthritis will develop
- To work out the best form of treatment
- To monitor drug therapy.
What is the diagnosis based on?
Remember that there are many different forms of arthritis. Your doctor will diagnose your arthritis by working through three sets of information:
- Your clinical history – what you have told your doctor
- Your clinical examination – what the doctor found by examining you
- The results of tests – which may be done to rule out more serious causes.
What types of tests are there?
There are many different tests and some are more routine than others. For example, the doctor can only work out your blood group if your blood has been tested for this. The blood is usually taken from a vein in your arm, using a needle and syringe, by either a doctor, nurse or phlebotomist (someone who is specifically trained to take blood). It is then stored in separate bottles (often different coloured) that contain different preservatives. It is then analysed in a laboratory. One blood bottle usually provides only one range of test results and cannot be used for other tests.
Remember that the results from these tests cannot usually be worked out straight away – some may take days or even weeks to come back from the laboratory. Blood results can also vary from day to day – this is quite normal, and so a small variation in a certain measurement may not be important. The most important measurements which are taken from blood tests are listed below:
Full blood count (FBC) This can help your doctor decide whether you have anaemia (lack of haemoglobin) and whether you have normal white cells (which fight infections) and normal platelets (which clot the blood). People with arthritis often have minor abnormalities of the full blood count. It can also be affected by certain drug therapies.
Erythrocyte sedimentation rate (ESR) This simple test measures how quickly the cells in the blood settle when they are left to stand in a tube. This reflects how much inflammation your arthritis has caused, and this measurement will improve if your arthritis improves. Some laboratories use other methods to work out the degree of inflammation, such as plasma viscosity (PV) or C-reactive protein (CRP) tests.
Biochemical profile A number of tests or markers in the blood can show how your liver and kidneys are working. Such tests may also assess the salt balance and calcium levels in your body. All of these can be affected by arthritis or by treatments.
Rheumatoid factor (RF) This is an antibody (see diagram below) that can be present in some people with arthritis. However, it is not only found in rheumatoid arthritis. There are people without arthritis who have this antibody, and up to a third of people with rheumatoid arthritis do not have it. It is a useful test only when it can be considered along with other findings. A positive test does not mean that you have rheumatoid arthritis. The amount of rheumatoid factor is expressed as a number.
Anti-nuclear antibodies (ANA) These antibodies are sometimes found in the blood of people with certain types of arthritis. Mainly these are diseases which can involve parts of the body other than just the joints (for example, organs such as the kidneys). The test is a useful screening test for lupus (systemic lupus erythematosus). There are several types of anti-nuclear antibodies which can help to make an accurate diagnosis.
Urate We all have urate in our blood. It is a waste product from the normal breakdown of protein and comes out in the urine. If the level builds up then some of it will solidify (precipitate) as crystals, particularly in the joints of the hands and feet. These crystals can cause severe inflammation which we call gout. The level of urate in the blood can help to make the diagnosis of gout and it can be used to monitor the response to treatment.
Other blood tests Other tests are used less often to measure levels of:
- Complement (this is used to measure disease activity in lupus)
- Levels of immunoglobulins (these help to fight infections and can change in some diseases)
- Specific antibodies to various infections which can start arthritis.
Genetic studies Very occasionally, genetic studies are done to help make the diagnosis. For example, we can test if the inherited antigen HLA-B27 is present, which can be associated with ankylosing spondylitis. Genetic studies are not useful in most cases.
IMPORTANT: If blood tests are recommended by your doctor, particularly for monitoring the effects of drugs, then it is essential that you have them done.
X-rays are the most tried-and-tested way of getting a picture of your bones and joints. X-rays will usually be done in a special hospital department (Radiology) by a radiographer, who will tell you which part of your body is to be x-rayed. Often patients who attend for the first time at a rheumatology department have a routine chest x-ray because chest diseases are sometimes associated with arthritis.
To make the image, x-rays are passed through your body and captured on an x-ray film. This film is then developed and examined. Standard x-rays are particularly good at showing abnormalities of the bone, but rarely show problems in other tissues. As a result, they do not show early arthritis very well. However, they can show things which help the doctor to diagnose arthritis, such as damaged areas on the bone.
The way bones appear on x-rays can vary in normal people and changes occur with age. For example, ageing abnormalities are frequently seen on x-rays of the spine, even in people without pain. Knowlege of the person with arthritis is essential to the interpretation of the x-rays.
Other methods of imaging
There are other ways of scanning the body to produce images and other ways of using x-rays, as well as the standard x-ray of the joint or bone:
Arthrography Some dye is injected into the joint to allow it to show up in more detail when x-rayed. Occasionally dye can be injected into a blood vessel to assess the circulation under x-ray (arteriogram or venogram).
Computerised tomography (CT) scan This provides a more detailed three-dimensional picture of the skeleton by cleverly adding up multiple x-ray images.
Isotope bone scanning A very small amount of radioactive-labelled marker is injected into the blood. This marker can help show which areas of the bone are inflamed.
Magnetic resonance imaging (MRI) scan Strong magnetic forces are used to produce pictures of the soft tissues which are not detected by x-rays, particularly cartilage, tendons and nerves. They can also show up signs of inflammation. They are particularly useful for the spine and the knee.
Dual emission x-ray absorptiometry (DEXA) This type of x-ray is used to assess the density of bones and is particularly useful for diagnosing and following osteoporosis.
Ultrasound This can be used to see if fluid has collected around joints and tendons. It can also be used to determine the risk of osteoporosis.
Synovial fluid analysis
All normal moving joints have a small amount of fluid in them to act as lubrication. If this fluid builds up it can make the joint swell. Examining this fluid can be very important in diagnosing infections or gout. For the examination, the fluid is taken from the joint using a needle and syringe. The needle does not go into the bone, but into the joint space (cavity) between the bones. This is often no more uncomfortable than having a blood test. Removing this fluid can also help to reduce discomfort and swelling. The fluid can then be examined in the laboratory.
A biopsy is when a small piece of tissue is removed from the body so it can be examined under the microscope. Virtually any body tissue can be biopsied and it can be done under general or local anaesthetic. It will only be done when it is absolutely necessary to work out a diagnosis. Some forms of arthritis can affect any areas of the body. This means it is essential to examine the tissue under the microscope to make the proper diagnosis and work out the treatment.
Testing the urine
This can help to make the diagnosis, and can also be used to check specific drug treatments.
Less common tests
Arthroscopy A small telescope is used to look inside the joint.
Nerve conduction studies (NCS/EMG) This is a way of assessing whether nerves and muscles are functioning correctly.
Electrocardiogram (ECG) This is used to decide how well the heart is working. It can be affected in some forms of arthritis and rheumatism.
Pulmonary function tests (PFTs) These are breathing tests to decide how the lungs are working. The lungs can be affected by arthritis, and also occasionally by treatment.
Looking to the future
As you can see from this booklet, the medical team now has a wide variety of tests and different techniques. Some are cheap and easy to carry out while some others are expensive and may only be done in special centres or may have long waiting times. Research is going on all the time to develop new and better tests to help the team diagnose and manage your arthritis. With your help, the Arthritis Research Campaign (arc) will continue to support this research.
Anaesthetic – a drug which removes sensation. With a local anaesthetic, the feeling is removed only from part of the body. With a general anaesthetic, the patient is unconscious.
Antibodies – blood proteins which are formed in response to germs, viruses or any other substances which the body sees as foreign or dangerous. The role of antibodies is to attack these foreign substances and make them harmless. However, in certain diseases (called autoimmune diseases) antibodies can attack the body’s own tissues.
Antigens – any substances which the body regards as foreign or potentially dangerous. Antigens cause the body to make antibodies in response (see above).
Anti-nuclear antibodies (ANA) – antibodies which are often found in the blood of people with ‘connective tissue diseases’ such as lupus and scleroderma. They can damage tissues in the body.
Complement – an enzyme ‘system’ in the blood. An enzyme is a substance which allows a biological reaction to take place. Complement is a ‘cascading enzyme system’, which means that, in it, a number of different enzymes are created or triggered one after another, thus allowing a number of reactions to take place. The complement system, consisting of at least 19 separate proteins, plays an important part in the body’s immune system, allowing foreign particles or micro-organisms to be made harmless, but also generating inflammation. The blood can be tested to find how much of each of the major elements of complement is present.
Computer tomographic (CT) scan – a type of scan which records images of sections or ‘slices’ of the body using x-rays. These images are then transformed by a computer into cross-sectional pictures.
EMG – electromyography. The process of recording the electrical activity of muscle. It can be used to test whether nerve impulses to the muscle are working normally and whether the muscle is responding as it should.
Erythrocyte – red blood cell.
Haemoglobin – is found in red blood cells and contains the pigment which gives blood its colour. Because it can combine with, and then release, oxygen, it allows the blood to carry oxygen around the body.
HLA-B27 – human leukocyte antigen B27. One of the HLA genes from the HLA-B family. HLA-B27, whilst not being the only determining factor in ankylosing spondylitis, is present in 95% of people with this condition. It is, however, present in 8% of the general population. Other diseases such as reactive arthritis and psoriatic arthritis can also be associated with HLA-B27.
Immunoglobulins – a class of blood proteins which are responsible for immunity to specific infections.
Magnetic resonance imaging (MRI) – a type of scan which uses high-frequency radio waves to build up pictures of the inside of the body. It works by detecting water molecules in the body’s tissue.
Plasma (blood plasma) – the pale-coloured liquid in which blood cells are suspended. It contains mineral salts, protein and trace elements.
Radiographer – someone who specialises in taking x-rays (radiographs).
Ultrasound scan – a type of scan which uses high-frequency sound waves to examine and build up pictures of the inside of the body.