Rheumatoid Arthritis (RA) Factor, C-reactive protein test

Rheumatoid Factor

About the Tests

This test detects and measures rheumatoid factor (RF), a type of “autoantibody”, in the blood. 

The rheumatoid factor (RF) test is used to help diagnose rheumatoid arthritis (RA) and to distinguish it from other forms of arthritis and other conditions that cause similar symptoms of joint pain, inflammation, and stiffness. 

In patients with symptoms and clinical signs of RA, the presence of significant concentrations of RF indicates that it is likely that they have rheumatoid arthritis (RA). 70-90% of patients with RA have positive RF test. In patients with symptoms of Sjögren’s syndrome, the presence of RF can indicate that they have the condition. RF is found in 75-95% of patients with Sjogren’s syndrome. 

The rheumatoid factor (RF) test may be requested with other autoimmune-related markers of inflammation, such as CRP (C-reactive protein) and ESR (erythrocyte sedimentation rate), and with FBC (Full Blood Count) to evaluate the body’s blood cells.

It must be interpreted in conjunction with the patient’s symptoms and history, and with tests of inflammation such as ESR or CRP. 

Purpose of the tests

The test for RF may be requested when a patient has signs of RA and these have persisted for more than 6 weeks. Symptoms may include:

• pain

• warmth

• swelling and morning stiffness in the joints,

• nodules under the skin

If the disease has progressed, evidence on X-rays of swollen joint capsules and loss of cartilage and bone. 

An RF test may be repeated when the first test is negative and symptoms persist. The RF test also may be requested when a patient has symptoms suggesting Sjögren’s syndrome. Symptoms may include an extremely dry mouth and eyes, and joint and muscle pain. Symptoms may also be mixed as patients may have more than one autoimmune disorder. Sjogren’s syndrome can occur by itself or following RA, or systemic lupus eryhtematosus (SLE). Patients with RA and/or Sjogren’s syndrome may also have other autoimmune diseases, such as thyroid disorders.

C-Reactive Protein (CRP)

About the Tests

C-reactive protein (CRP) is an acute-phase reactant, a protein made by the liver that is released into the blood within a few hours after tissue injury, the start of an infection, or other inflammation. 

Increased concentrations in the blood can be found after a heart attack, in sepsis, and after a surgical procedure. It is often the first evidence of inflammation or an infection in the body, with rising concentrations frequently preceding pain, fever, or other clinical indicators. 

Purpose of the tests

To identify the presence of inflammation, determine its severity, and monitor response to treatment. When your doctor suspects that you might be suffering from an inflammatory disorder (as with certain types of arthritis and autoimmune disorders or inflammatory bowel disease) or to check for the possibility of infection (especially after surgery)

The CRP blood test is not diagnostic, but it provides information to the doctor on whether inflammation is present. This information can be used in conjunction with other factors, such as signs and symptoms, physical examination. The doctor may then follow up with further testing and treatment.