Rheumatoid arthritis endpoints are built from the same core set: tender and swollen joint counts, global assessments, pain, function and an acute phase reactant. Capture them once, at joint level, and both ACR response and DAS28 can be derived.
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28-joint count
Tender joints (0 to 28)
Swollen joints (0 to 28)
Patient global assessment of disease activity
CRP
At a glance
The core set
Rheumatoid arthritis trials almost always report ACR20 as a primary or key secondary endpoint and DAS28 as a measure of disease activity, often alongside EULAR response and remission rates. All of them draw on the same core set of measurements recorded at each assessment visit. If the eCRF stores each component (ideally at joint level for the counts), every one of these endpoints can be calculated in analysis, and a changed definition later does not require re-entering data.
Joint counts are best recorded joint by joint, with tender and swollen as separate answers for each joint, using a table section with one row per joint. That supports both the 28-joint count used in DAS28 and the 68/66 counts used in ACR response, and lets monitors verify individual joints against source.
DAS28-ESR is calculated as 0.56 × √(tender 28) + 0.28 × √(swollen 28) + 0.70 × ln(ESR) + 0.014 × patient global health. A CRP-based version uses a different constant and coefficient for CRP, and the two versions are not interchangeable. State which one the protocol uses, and record the lab value it needs. Capture stores the components; the score is derived in analysis.
The Health Assessment Questionnaire Disability Index measures physical function and is one of the ACR core set components. It is a participant-reported questionnaire and can run on the participant's phone before the visit; check the licensing terms for the version you use.
Week 12 DAS28
3.9 / 9.4
Structure
| Component | Used in | Captured as |
|---|---|---|
| Tender joint count (68) | ACR | Table section, one row per joint |
| Swollen joint count (66) | ACR | Same table, swollen column |
| Tender and swollen counts (28) | DAS28 | Subset of the same joint table |
| Patient global assessment | ACR, DAS28 | Slider 0 to 100, no preset value |
| Physician global assessment | ACR | Slider 0 to 100, site form |
| Patient pain | ACR | Slider or numeric scale |
| HAQ-DI | ACR | ePRO questionnaire |
| CRP or ESR | ACR, DAS28 | Lab form with units and ranges |
Joint assessor
Joint counts vary between assessors, so RA trials use trained assessors who are blinded to treatment and ideally assess the same participant throughout. Capture attributes every value to the person who entered it and keeps treatment allocation hidden from blinded roles.
Study coordinator
Subject 01-004
Randomized · R-0012
KitK-10418
Arm columnNot sent
Unblinded administrator
Subject 01-004
Randomized · R-0012
KitK-10418
Arm columnA
Same subject, same screen. The arm never reaches blinded roles.
Add the RA core set to a visit and test it with sample data.
Related endpoints
The EULAR response criteria classify each participant as a good, moderate or non-responder from two things: how much DAS28 improved from baseline and where it ended up. Broadly, a good response means an improvement of more than 1.2 with a final DAS28 of 3.2 or less; smaller improvements, or large improvements that leave disease activity high, give moderate or no response. Because EULAR response is derived from DAS28, it needs no additional data if the components are captured.
Two simpler composite indices are also common. The Clinical Disease Activity Index (CDAI) adds the 28-joint counts to patient and evaluator global assessments and needs no laboratory value, which makes it usable at the visit. The Simplified Disease Activity Index (SDAI) adds CRP to the same components. Capturing the evaluator global assessment alongside the ACR core set lets you derive all of them.
Before go-live
28 and 68/66 joints as table rows, tender and swollen columns.
ESR or CRP, stated in the protocol and analysis plan.
Patient and evaluator global wording and anchors fixed.
Joint assessor separate from treating investigator where possible.
Terms confirmed and recorded on the form if required.
CRP or ESR collected at the same visit as joint counts.
At least 20% improvement in tender and swollen joint counts plus at least 20% improvement in three of five other core set measures.
From 28-joint tender and swollen counts, ESR or CRP, and patient global health. The ESR and CRP versions use different formulas.
Below 2.6 is commonly used as remission; above 5.1 indicates high disease activity.
Yes, ideally. Joint-level data supports both 28 and 68/66 counts and can be verified against source.
Capture stores the components as structured fields; DAS28 and ACR response are derived in analysis.
Joint-level data for every RA endpoint. Free sandbox.