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Diagnosing arthritis can often be a difficult task due to the general nature of the symptoms. This article outlines the different blood tests that doctors will use in order to determine a diagnosis of arthritis.

Arthritis is a condition that is characterized by joint inflammation and develops in patients of all ages. Arthritis can be a hard condition to diagnose as there is no one single test that can confirm the presence of the disease. Instead, the disease is diagnosed based on a number of different criteria, including symptoms, physical examination and a number of blood and imaging tests.

There are several different types of blood tests that a doctor can order to determine whether or not you have arthritis. A blood test will often be ordered on an initial visit to the doctor and will also be a part of follow-up appointments as blood tests can help evaluate disease progression and whether you are or not responding to a particular therapy.

What types of blood tests might your doctor order?

1. A complete blood cell count

Through the use of a complete blood count, the doctor is able to determine the levels of different types of cells in the blood including red blood cells, white blood cells and a compound involved in blood clotting known as platelets. While a complete blood count won’t tell you whether you have arthritis, it can inform you if you have a problem, as abnormal cell counts are often indicative of some type of disease. This is the type of information you can glean from a complete blood count:

  • If the white blood cell count is high (generally above 11,000 cells), then that means that there is inflammation in the body. White blood cells are the main components of the immune system so when the immune system becomes activated (as in the case of arthritis), that leads to a rise in white blood cells. Hence, elevated white blood cell levels can indicate the presence of arthritis. On the other hand, several other diseases and infections can also raise levels of white blood cells in the body.
  • Hemoglobin in a normal part of red blood cells and is vital as it is the compound that carries oxygen around the whole body. A complete blood count also measures hemoglobin levels. In some people with arthritis, the hematocrit, which is the percent of total blood that is made up of red blood cells, can be low. Again, this is not specific to arthritis.

2. Erythrocyte sedimentation rate

This test measures how fast the red blood cells in your body settle at the bottom of a tube. Generally, the higher the erythrocyte sedimentation rate, the higher the levels of inflammation in the body. This is because inflammation in blood causes the red blood cells to bunch together and fall faster. Generally, a reading of erythrocyte sedimentation rate of over 100 mm/hour means that you likely have inflammation in the body. Again, this test will only tell you if you have an inflammatory condition and won’t tell you whether you specifically have arthritis.

3. Rheumatoid factor

This is a type of protein known as an antibody. Antibodies are an important component of our immune system that recognize foreign pathogens in the body and stimulate an immune response again then. Patients with arthritis will often have this antibody in their body, which is why doctors will order this test. However, other inflammatory conditions can also have rheumatoid factor.

4. Antinuclear antibody

Several different types of autoimmune diseases have antibodies that are targeted towards the nucleus of cells (the part of cells that houses the DNA). Therefore, doctors will order a blood test for antinuclear antibody as it can be informative about whether or not you have an autoimmune disease. This type of antibody can actually be seen by looking a patient’s serum (a component of blood) under a microscope.

5. C-reactive protein

C-reactive protein is a type of protein that is made by your liver as a response to inflammation in the body. While normal people have less than 10 mg/L of C-reactive protein in the body, a patient with an inflammatory condition will have significantly more. This test is often administered to monitor how well you are responding to anti-inflammatory treatment. Unfortunately, this test is also not specific for arthritis.

6. HLA-B27

People with arthritis often have a gene that is not frequently present in the healthy population. This gene is called HLA-B27 and it provides the instructions to make a protein. This protein is then displayed on the surface of white blood cells. Therefore, using a blood test, doctors can look for levels of HLA-B27. This gene is present in patients with a range of autoimmune disorders but is frequently seen in patients with arthritis.

7. Creatine kinase

This is a type of protein known as an enzyme that is produced by your body in response to inflammation. In particular, people have high levels of creatine kinase after they experience some sort of trauma, but can also be present in inflammatory muscle disease.

Unfortunately, there is no one single diagnostic test that can confirm whether you have arthritis. However, the blood tests described here can provide your doctor with evidence for a diagnosis of the disease as well as exclusion of other diseases.

  • Li, S. F., et al. "Diagnostic utility of laboratory tests in septic arthritis." Emergency Medicine Journal 24.2 (2007): 75-77.
  • Li, Siu Fai, et al. "Laboratory tests in adults with monoarticular arthritis: can they rule out a septic joint?." Academic emergency medicine 11.3 (2004): 276-280.
  • Nielen, Markus MJ, et al. "Increased levels of C‐reactive protein in serum from blood donors before the onset of rheumatoid arthritis." Arthritis & Rheumatism: Official Journal of the American College of Rheumatology 50.8 (2004): 2423-2427.
  • Sox, Harold C., and Matthew H. Liang. "Diagnostic decision: the erythrocyte sedimentation rate: guidelines for rational use." Annals of internal medicine 104.4 (1986): 515-523.
  • Photo courtesy of SteadyHealth

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