A simple, validated composite score for RA disease activity that requires no laboratory values. Based solely on joint counts and global assessments from both the physician and patient. Ideal for point-of-care use when lab results are not available.
The CDAI is a simplified version of the SDAI that removes the CRP requirement, making it practical for real-time point-of-care use. It sums four variables: the 28-joint tender count, 28-joint swollen count, physician global assessment, and patient global assessment, each on a 0-10 scale. The maximum possible score is 76.
Because no laboratory value is needed, CDAI scores can be calculated and interpreted immediately during any clinic visit without waiting for lab results. It correlates strongly with both the SDAI and DAS28, and has been validated as a treat-to-target instrument.
Use the CDAI when you need a disease activity score immediately, when lab results are not yet back, or when you want to avoid the slight complexity of the DAS28 formula. It is especially useful in community rheumatology settings where CRP is not always ordered at every visit.
It is also the preferred score for some biologic prescribing pathways in certain health systems, so knowing which score is required in your setting is important. The ACR and EULAR both recognize CDAI as a valid treat-to-target monitoring instrument.
| CDAI Score | Activity State | Clinical Meaning |
|---|---|---|
| 0 to 2.8 | Remission | Treat-to-target goal. ACR/EULAR recommend aiming for this state. |
| 2.8 to 10 | Low Activity | Acceptable alternative target if remission is not achievable. |
| 10 to 22 | Moderate Activity | Consider therapy adjustment. Biologic eligibility threshold in many systems. |
| > 22 | High Activity | Active disease. Treatment escalation is warranted. |
The CDAI was developed by Aletaha and Smolen and published in Arthritis and Rheumatism in 2005. It was derived by removing the CRP component from the SDAI and demonstrating that the resulting four-variable index maintained strong correlation with the full SDAI and adequately discriminated between response states.
Validation against ACR/EULAR Boolean remission criteria demonstrated that CDAI remission below 2.8 had a high positive predictive value for Boolean remission, supporting its use as a treat-to-target instrument. The score has been incorporated into multiple ACR and EULAR treatment recommendations and biologic prescribing guidelines.