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Friday, 20 October 2017
Blood Monitoring

All disease-modifying anti-rheumatic drugs (DMARDs) have the potential to cause adverse effects and thus require regular monitoring to ensure your safety.

DMARDs are excreted mainly via the liver and kidneys and may affect either organ adversely. They can also have adverse effects on the blood.

Regular blood tests are important both to check for adverse effects and to monitor how active your disease is and how well you are responding to treatment. Samples are usually taken from a vein in your arm or the back of your hand. This can be done at the hospital pathology department by a phlebotomist but many GP practices also provide a phlebotomy service – if this would be more convenient for you please check that your surgery offers this service.

For patients on DMARDs regular blood tests usually include the following: full blood count (FBC), erythrocyte sedimentation rate (ESR) and biochemical profile (liver function tests (LFTs), C-reactive protein (CRP) and sometimes renal (kidney) function tests (urea, electrolytes and creatinine)).

A full blood count includes the haemoglobin, white cell count and platelet (thrombocyte) count. These are briefly explained below.

Haemoglobin
If you become anaemic your haemoglobin level will decrease. Anaemia is common in many forms of arthritis and may be due to a number of reasons. Iron deficiency is a common cause and iron or dietary supplements may be necessary. Non-steroidal anti-inflammatory drugs (NSAIDs) are known to cause stomach irritation (gastritis) and ulceration in some people. This may lead to bleeding from the stomach or bowel resulting in anaemia.

Other causes of anaemia include malabsorption (where certain nutrients are poorly absorbed via the bowel) – this may occur if you have other conditions such as Crohn’s disease or coeliac disease. Some people have a form of anaemia called pernicious anaemia, which requires regular injections of Vitamin B12. Anaemia commonly occurs as a symptom of chronic inflammation, however, and is not always helped by iron supplements. However, as your arthritis comes under better control the haemoglobin often improves and the anaemia resolves. Very occasionally severe anaemia requires a blood transfusion.

White cell count
The white blood cells may be affected by both your disease and its treatment. The number often increases when infection is present, or with long-term use of corticosteroids. However drugs which suppress the immune system may reduce the number of white cells. The number of white cells is checked to ensure that you retain sufficient to fight infection. There are different types of white cells; the most important being neutrophils. If the level of neutrophils falls too low you may need to stop treatment.

Platelets
The number of platelets in the blood is also monitored. These are cells involved in blood clotting and may increase in number when there is active inflammation. Some drug treatments may cause a reduction in platelets which could increase the risk of bleeding, making it necessary to stop treatment.

Erythrocyte sedimentation rate (ESR)
The ESR is a simple test which indicates the level of inflammation in the blood and may increase when your arthritis is more active, but this is not always the case: in some conditions the ESR remains normal despite ongoing inflammation. The ESR may also be affected by concurrent illness or infection. The ‘normal’ ESR varies: it is often higher in women and increases with age.

Some hospitals use a different test, the plasma viscosity, which also measures the level of inflammation in the body.

Biochemistry Tests (LFTs, U&Es, Creatinine) check how well your liver and kidneys are working, by assessing the balance of salts and calcium levels in the body. These can be affected by many conditions and by drug treatments.

C-reactive protein (CRP) is an enzyme produce by the liver which increases in response to inflammation. It is usually included with other liver tests to provide an additional means of assessing the extent of your disease activity.

Further information about these and other blood tests used in rheumatology is available from Arthritis Research Campaign