Measuring RA with ACR Score

A number indicating how much a person’s rheumatoid arthritis (RA) has improved, based on guidelines set forth by the American College of Rheumatology (ACR). The ACR score represents a percentage. An ACR20 score means that a person’s RA has improved by 20%, an ACR50 score means it has improved by 50%, and an ACR70 score means it has improved by 70%.

To qualify for an ACR20 score, a person with RA must have at least 20% fewer tender joints and at least 20% fewer swollen joints. As well, he or she must show a 20% improvement in at least three of the following five areas: the person’s overall (global) assessment of his or her own RA, the physician’s global assessment of the person’s RA, the person’s assessment of his or her own pain, the person’s assessment of his or her own physical functioning, and the results of an erythrocyte sedimentation rate or C-reactive protein blood test (both of which test for inflammation). ACR50 and ACR70 scores use the same criteria but require 50% and 70% improvement, respectively.

The ACR score is more often used in clinical trials than by individual doctors treating patients. It used to be that different researchers studying different RA treatments would measure different things. That meant there was no common standard to judge the different treatments against. The ACR score provides that standard. Using the ACR score also has other benefits. For example, because it standardizes what is to be measured, researchers can’t pick and choose what to report, so study results are more likely to be reliable.

Robert S. Dinsmoor is a medical writer and editor based in Massachusetts.

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