Understanding ACR20 (American College of Rheumatology) Criteria

In clinical trials for rheumatoid arthritis, standard criteria are used to compare the effectiveness of arthritis medications or arthritis treatments, or to compare one trial to another. The criteria, known as American College of Rheumatology (ACR) criteria, is the measure used in nearly all published studies that look at the efficacy (effectiveness) of treatments for all types of rheumatic diseases. ACR20 was the first set of criteria established, followed later by ACR50 and ACR70.

The Use of ACR Criteria

ACR criteria are used to assess and establish the improvement in tender or swollen joint counts along with improvement in three of the following five parameters:

• Acute phase reactant: How much inflammation is in your joints as determined by C-reactive protein or sedimentation rate.
• Patient assessment: How you see your progress and response to treatment.
• Healthcare provider assessment: What your healthcare provider observes in your progress and response to treatment.
• Pain scale: How much pain you're having in your joints on a daily basis.
• Disability/functional questionnaire: How much your rheumatoid arthritis is interfering with your ability to do your daily activities.

ACR criteria can also be used to help healthcare providers more effectively determine if your treatments are working to improve your rheumatoid arthritis symptoms, though they are more often used for clinical trials.

Understanding What ACR20, ACR50, and ACR70 Indicate in Clinical Trials

Clinical trials report the percentage of study participants who achieved ACR20, ACR50, and ACR70. For example, if a study reported that 55 percent of patients achieved ACR20, that means 55 percent of patients in the study achieved a 20 percent improvement in tender or swollen joint counts, as well as 20 percent improvement in three of the other five criteria.

If a clinical trial reports that 40 percent of patients achieved ACR50, that means 40 percent of patients in the study achieved a 50 percent improvement in tender or swollen joint counts, as well as 50 percent improvement in three of the other five criteria. The same applies to ACR70, only with a 70 percent improvement level. For patients to be assessed using ACR criteria, they must have completed the clinical trial.

ACR20 Is FDA Approved

The U.S. Food and Drug Administration (FDA) recommended the use of ACR20 as the outcome measure of choice for clinical trials of drugs used to treat rheumatoid arthritis. This endorsement led to the widespread use of ACR20 in clinical trials. It's commonly referred to as simply ACR20 because it requires at least a 20 percent improvement in the criteria above.