Tools Your Doctor Will Use to Diagnose RA
Your doctor has a number of tools he or she will use to help determine whether you have RA. The most important tool for diagnosis of RA is a thorough physical examination. Other tools that are typically used in diagnosis, as well as in determining disease severity, include medical history, laboratory testing, imaging (x-ray and other types of imaging), and special tests, such as joint aspiration, arthroscopy, and synovial fluid analysis.
During the medical history, your doctor will ask questions about your symptoms, family medical history, other medical problems, and any medications you may be taking. Your doctor will be interested in learning about the type of pain you are experiencing, its location and pattern (whether it involves both knees or hips or only joints on one side), how it affects your mobility and lifestyle, and whether it is affecting your sleep and causing fatigue. Your doctor will also want to know about other medical problems you have. Additionally, it is important to give your doctor a complete list of any medications and vitamins/supplements you are currently taking.
It may help to gather your thoughts and collect information related to each of these areas before you go to your initial appointment.
A thorough physical examination is absolutely vital and often the primary tool used to diagnose RA. Your doctor will check general health parameters, including blood pressure, pulse rate, heart and lung function, and will evaluate your joints in great detail, paying particular attention to function, swelling, and pain.
Laboratory testing is an important part of forming a complete picture to help determine your diagnosis. There are certain substances that tend to be present in the blood of patients with RA or elevations of common components of blood that are suggestive of inflammatory disease. Laboratory tests for RA commonly look at:
- Rheumatoid factor (RF)
- Anti-citrullinated protein antibodies (ACPA) (including anti-cyclic citrullinated peptide [anti-CCP] and anti-mutated citrullinated vimentin [MCV] antibody tests)
- Erythrocyte sedimentation rate (ESR)
- C-reactive protein (CRP)
- Antinuclear antibody (ANA)
- Complete blood count (CBC)
There are several survey-type tools that have been developed to help doctors determine extent of RA disease activity. These usually focus on joint activity, swelling, pain levels, and disability. Some, like the DAS 28 include blood tests in the assessment. These measures include, but are not limited to the following: 1-3
- Health Assessment Questionnaire (HAQ): consists of the Physician Global Assessment (PGA), which is a binary yes/no clinical evaluation of presence of pain or swelling in any of 13 joints, bilaterally and the Patient Global Assessment (PtGA) asks patients to rate pain on a linear scale and to assess their ability to perform everyday tasks.
- Disease Activity Score for 28 joints (DAS 28): combines single measures into an overall continuous measure of RA disease activity. It includes a 28-swollen joint count (28SJC), 28-tender joint count (28TJC), erythrocyte sedimentation rate (ESR) and a PtGA or general health (GH) on a visual analog scale (VAS) for pain. It results in an overall disease activity score of high, low, or remission.
- Clinical Disease Activity Index (CDAI): combines single measures into an overall continuous measure of RA disease activity. The CDAI includes a 28SJC, 28TJC, PtGA on a 10-cm VAS, and provider global assessment of disease activity (PrGA) on a 10-cm VAS.
- American College of Rheumatology 20 (ACR 20): evaluates clinical improvement relative to an initial assessment and is commonly used as an efficacy endpoint for clinical trials in patients with RA. The ACR20 denotes at least 20% improvement in tender and swollen joint counts and in three of the following end points: global assessment by patients, global assessment by doctors, ESR or C reactive protein (CRP), patient’s pain VAS, and Health Assessment Questionnaire Score
- Routine Assessment of Patient Index Data (RAPID 3): includes a subset of core variables found in the Multi-dimensional HAQ (MD-HAQ), including an assessment of physical function, a PGA for pain, and a PGA for global health. RAPID3 scores are tallied by adding subsets of the MD-HAQ.
Your rheumatologist may have used one or more of these tools for initial diagnosis and to monitor treatment effectiveness over time. These tools are also used for drug development and testing. Unlike objective physical measurements like weight or height, these tools involve some level of subjectively based on perceptions of the patient, doctor, or both.
Your doctor may have x-rays taken of symptomatic joints. X-rays can reveal certain signs of joint involvement (inflammation) and damage (bone erosion) that are indicative of RA. Other imaging tests that may be useful in diagnosis of RA include magnetic resonance imaging (MRI) and ultrasound.
Other specialized tests
Other specialized tests that may be useful in assessing selected patients include analysis of synovial fluid, arthroscopy, and laboratory tests to detect possible infection.
Synovial fluid analysis is performed by using a needle to take a sample of the fluid inside your joint cavity. Several tests are then performed on the synovial fluid, including a count of the cells present in the fluid, a search for uric acid crystals that may indicate gout, and a gram stain and culture to detect possible infection.
Arthroscopy involves inserting a fiberoptic camera through a tube (about the size of a straw) into the joint space to examine the interior of the joint. This procedure can be used to aid diagnosis. Sometimes a second incision is made and small surgical instruments are also inserted into the joint space through another tube for making repairs to damaged joint tissues or for removing bone or cartilage.
Laboratory tests of blood and other fluids, especially in patients who test negative for RF and anti-CCP antibodies, may be useful in detecting an infection, such as Lyme disease or hepatitis B virus (HBV) or hepatitis C virus (HCV).
- Anderson JK, Zimmerman L, Caplan L, Michaud K. Measures of Rheumatoid Arthritis Disease Activity Arthritis Care & Research Vol. 63, No. S11, November 2011, pp S14–S36.
- Goldman JA, Xia HA, White B, Paulus H. Evaluation of a modified ACR20 scoring system in patients with rheumatoid arthritis receiving treatment with etanercept. Ann Rheum Dis. Dec 2006; 65(12): 1649–1652.
- Baron-Faust R, Wingerson L. RA Outcome Measures Made Simple (or Not?). Available at: http://www.rheumatologynetwork.com/rheumatoid-arthritis/ra-outcome-measures-made-simple-or-not/ Accessed June 16, 2014.