ACR/EULAR Boolean and Index Remission Interpreter

ACR/EULAR Boolean and Index Remission Interpreter

All four ACR/EULAR remission definitions on one patient: the 2011 Boolean criteria, the 2022 revision that moved the patient global from 1 to 2, and the index-based SDAI definition — which classify different patients.

Last updated 8 Oct 2026

ACR/EULAR remission

6 inputs → which definitions are met
The Boolean criteria require 1 or less. The 2011 committee tested joint counts on both the 28-joint and the 66/68-joint sets; the published threshold is the same number either way, which means it is a stricter criterion on the larger count.
The Boolean criteria require 1 or less. Note that the Boolean definition allows ONE swollen joint, which is why ‘remission’ here is not the same statement as ‘no synovitis’.
On a 0–10 cm scale. THIS IS THE ITEM THE 2022 REVISION CHANGED, from 1 or less to 2 or less, and the only item it changed. It is also the item that most often prevents Boolean remission in a patient the index definition calls remitted. On a 0–10 scale. Trials record this on a 0–100 mm visual analogue scale and DIVIDE BY TEN before summing, so a mark at 45 mm is entered here as 4.5. Entering the millimetre figure unchanged would add 45 points to a score whose remission cut-off is 2.8.
On a 0–10 cm scale. THE BOOLEAN DEFINITION DOES NOT TEST THIS ITEM AT ALL; the index-based definition includes it in the SDAI sum. That asymmetry is one of the two reasons the definitions disagree, and it means a patient can pass all four Boolean thresholds and still fail the index definition on the assessor’s opinion alone. On a 0–10 scale. Trials record this on a 0–100 mm visual analogue scale and DIVIDE BY TEN before summing, so a mark at 45 mm is entered here as 4.5. Entering the millimetre figure unchanged would add 45 points to a score whose remission cut-off is 2.8.
Enter the figure your laboratory reported and set the unit below. The Boolean limit is 1 mg/dL, which is 10 mg/L — a figure a great many patients in remission sit below.
The formula wants mg/dL. Selecting mg/L divides your entry by ten before it is added. This select exists because the unit is where implementations of this index go wrong: a CRP of 10 mg/L is 1.0 mg/dL, and adding 10 instead of 1 moves the total by exactly 9 points. CRP unit converter
Boolean 2.0 (2022 revision) met; Boolean 1.0 and index-based (SDAI) remission NOT metExample

Tender joint count 1, swollen joint count 1, patient global 1.5, evaluator global 0.4, CRP 4 mg/L

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Four definitions, three of them tested here, and the one item that separates them

Boolean 1.0 (2011) — ALL FOUR, simultaneously: tender joint count ≤ 1 · swollen joint count ≤ 1 · CRP ≤ 1 mg/dL · patient global ≤ 1 (0–10)
Boolean 2.0 (2022 revision) — the same four with patient global ≤ 2
Index-based — SDAI ≤ 3.3, where SDAI = tender + swollen + patient global + evaluator global + CRP in mg/dL
Three-variable Boolean / CDAI ≤ 2.8 — the alternatives where no CRP is available
ALL FOUR, simultaneously
the Boolean definition trades nothing off against anything. One item above its limit means the definition is not met, however low the other three are. The index definition is the opposite: five terms summed, so a high value anywhere can be offset elsewhere
CRP ≤ 1 mg/dL
which is 10 mg/L. This formula takes CRP in mg/dL, not mg/L. A laboratory reporting 4 mg/L is reporting 0.4 mg/dL, and entering the SI figure as though it were conventional multiplies that term by ten. CRP unit converter
patient global ≤ 1, or ≤ 2
the ONLY item the 2022 revision changed. The thresholds in 2011 came mainly from a committee survey whose answers clustered around 1, and were then tested for their ability to predict stable radiographs and a stable disability index of 0.5 or less in the second year
the evaluator global
in the index definition and NOT in the Boolean one. This is the asymmetry that lets a patient pass all four Boolean thresholds and fail the index definition
which definition to report
the 2011 paper is explicit that these are definitions for clinical trials, and offers the Boolean and index-based forms as alternatives rather than ranking them. The 2022 revision recommends the revised Boolean definition and the SDAI and CDAI definitions for both trials and practice, and was approved by the ACR Board and the EULAR Executive Committee
not DAS28 remission
a DAS28 below 2.6 is a different and looser definition, and the 2011 committee found the DAS28 definitions predicted radiographic outcome poorly where these did not. DAS28-ESR covers that

Worked example

Tender joint count 1, swollen joint count 1, patient global 1.5, evaluator global 0.4, CRP 4 mg/L
CRP: 4 mg/L ÷ 10 = 0.4 mg/dL, well inside the 1 mg/dL limit
Boolean 1.0: tender 1 ✓, swollen 1 ✓, CRP 0.4 ✓, patient global 1.5 ✗ — not met, on one item
Boolean 2.0: the same four with the patient global limit raised to 2 — 1.5 ✓, so met
SDAI: 1 + 1 + 1.5 + 0.4 + 0.4 = 4.3, which is above 3.3 — index-based remission not met
So one definition of three is satisfied, and which one depends on which published document is being followed
DISAGREEMENT IN THE OTHER DIRECTION: tender 1, swollen 1, patient global 1, CRP 10 mg/L (= 1.0 mg/dL) and an evaluator global of 3. Every Boolean threshold is met exactly, and the SDAI is 1 + 1 + 1 + 3 + 1 = 7.0 — Boolean remission without index remission, decided entirely by the assessor's global score, which the Boolean definition never reads
AND THE COMMONER DIRECTION: tender 0, swollen 0, patient global 3, evaluator global 0, CRP 2 mg/L. SDAI = 0 + 0 + 3 + 0 + 0.2 = 3.2, so index-based remission is met, and both Boolean definitions fail on the patient global alone
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What each definition tests

ItemBoolean 1.0Boolean 2.0Index (SDAI)
Tender joint count≤ 1≤ 1added to the sum
Swollen joint count≤ 1≤ 1added to the sum
Patient global (0–10)≤ 1≤ 2added to the sum
CRP (mg/dL)≤ 1≤ 1added to the sum
Evaluator global (0–10)not testednot testedadded to the sum
How the items combineall four must holdall four must holdtotal ≤ 3.3
Two asymmetries generate every disagreement between these definitions. The index counts a term the Boolean definitions never read, and the Boolean definitions gate on each item where the index lets them trade off. Neither is a refinement of the other; they are different instruments published side by side.

What the 2022 revision did, measured

FigureBoolean 1.0Boolean 2.0
Remission at 6 months, early RA (n = 1,101)14.8%20.6%
Remission at 6 months, established RA (n = 947)4.2%6.0%
Kappa against the SDAI definition0.770.86
Kappa against the CDAI definition0.760.81
Concordance with the SDAI, overall93.4%95.9%
Concordance with the SDAI, established RA74%94%
From four randomised trials of biologic agents against placebo — GO-AFTER, FUNCTION, LITHE and SERENE — with 2,048 participants and a mean disease duration of 0.8 years in the early cohort and 7.1 in the established one. Raising the patient global threshold by one point increased remission rates by about 40% relative AND improved agreement with the index definition, which is unusual: loosening a criterion normally costs agreement. Removing the item altogether was tested and rejected because it predicted outcome worse.

Two definitions of the same word, the item that separates them, and what 2022 changed

The ACR and EULAR published two definitions of remission in 2011, not one, and they were explicitly provisional and explicitly for clinical trials. The Boolean definition requires a tender joint count of 1 or less, a swollen joint count of 1 or less, a CRP of 1 mg/dL or less and a patient global assessment of 1 or less on a 0–10 scale — all four at once, with nothing traded off against anything. The index-based definition requires an SDAI of 3.3 or less. The committee arrived at the ≤ 1 thresholds mainly from a survey of its own members whose answers clustered around 1, then tested the candidates for predictive validity against stable radiographs and a stable disability index of 0.5 or less in the second year of follow-up. The DAS28 definitions were tested too and predicted radiographic outcome poorly, which is why a DAS28 below 2.6 is not among these.

The two definitions do not agree, and the reasons are structural rather than statistical. The SDAI carries the evaluator global assessment, which neither Boolean definition tests — so a patient can pass all four Boolean thresholds and fail the index definition on the assessor’s opinion alone. And the Boolean definition gates on each item where the index lets them offset: a patient with no tender or swollen joints, a CRP of 2 mg/L and a patient global of 3 has an SDAI of 3.2, which is index-based remission, and fails both Boolean definitions on the global alone. In the 2022 validation overall concordance between the original Boolean definition and the SDAI was 93.4%, so roughly one patient in fifteen is classified differently depending on which definition a trial chose — and in established rheumatoid arthritis concordance was only 74%.

The 2022 revision changed exactly one number. Studenic and colleagues, using four randomised biologic trials and 2,048 participants, raised the patient global threshold from 1 cm to 2 cm and left the tender count, swollen count and CRP alone. Remission at six months rose from 14.8% to 20.6% in early disease and from 4.2% to 6.0% in established disease, relative increases of about 39% and 42%. What makes the change interesting is that agreement with the index definition improved at the same time — kappa against the SDAI from 0.77 to 0.86, concordance in established disease from 74% to 94% — which is not what loosening a criterion usually does. The authors also tested dropping the patient global entirely: remission rose further, to about 27% and 10%, but agreement fell and the definition predicted a good functional and combined outcome less well. The item earns its place; its threshold was simply set too tight.

The practical consequence is that ‘in remission’ is not a single fact about a patient. Three definitions are computed here and a fourth exists for settings with no CRP — the three-variable Boolean definition and CDAI of 2.8 or less, both validated in the same 2022 work with a positive likelihood ratio of roughly 3.8 to 4.3 for a good combined outcome at one year. This formula takes CRP in mg/dL, not mg/L. A laboratory reporting 4 mg/L is reporting 0.4 mg/dL, and entering the SI figure as though it were conventional multiplies that term by ten. The 1 mg/dL Boolean limit is 10 mg/L, so a reader entering an SI figure unchanged will reject remission in almost everyone. SDAI prints the index total and its band, DAS28-ESR covers the looser DAS28 definition and why it was not adopted, and EULAR DAS28 response criteria and ACR20, ACR50 and ACR70 answer the different question of how much a patient has improved.

Frequently asked questions

What is the ACR/EULAR Boolean definition of remission?

A tender joint count of 1 or less, a swollen joint count of 1 or less, a CRP of 1 mg/dL or less, and a patient global assessment of 1 or less on a 0–10 scale — all four simultaneously. The 2022 revision raised the patient global threshold to 2 and left the other three unchanged. Nothing is traded off: one item above its limit means the definition is not met.

What is the index-based definition?

An SDAI of 3.3 or less, where the SDAI is the tender joint count plus the swollen joint count plus the patient global plus the evaluator global plus CRP in mg/dL. A CDAI of 2.8 or less is the equivalent where no CRP is available. Both were validated rather than altered by the 2022 revision.

How often do the Boolean and index definitions disagree?

In the 2022 validation, across four randomised trials and 2,048 participants, overall concordance between the original Boolean definition and the SDAI was 93.4% — so about one patient in fifteen was classified differently. In established rheumatoid arthritis concordance was only 74%. Under the revised Boolean definition those figures rose to 95.9% and 94%.

Why can a patient meet the Boolean definition and not the index one?

Because the SDAI includes the evaluator global assessment and the Boolean definition does not test it at all. With one tender joint, one swollen joint, a patient global of 1 and a CRP of 1 mg/dL the four Boolean items already contribute 4 to the SDAI, so the assessor’s own score decides the index definition on its own.

What did the 2022 revision change?

Only the patient global assessment threshold, from 1 cm to 2 cm. Remission at six months rose from 14.8% to 20.6% in early disease and 4.2% to 6.0% in established disease, and agreement with the index definition improved at the same time — kappa against the SDAI from 0.77 to 0.86. Removing the item entirely was tested and rejected because it predicted outcome worse.

Is a DAS28 below 2.6 the same as ACR/EULAR remission?

No, and it is looser. The 2011 committee tested DAS28 definitions and found they predicted radiographic outcome poorly where the Boolean, SDAI and CDAI candidates performed similarly. A patient can be in DAS28 remission with a swollen joint and a raised CRP, because the DAS28 weights its terms and lets them offset.

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References

  1. Felson DT, Smolen JS, Wells G, et al. American College of Rheumatology/European League Against Rheumatism provisional definition of remission in rheumatoid arthritis for clinical trials. Ann Rheum Dis. 2011;70(3):404–13.
  2. Studenic P, Aletaha D, de Wit M, et al. American College of Rheumatology/EULAR remission criteria for rheumatoid arthritis: 2022 revision. Ann Rheum Dis. 2023;82(1):74–80.
  3. MSB11456 in participants with moderately to severely active rheumatoid arthritis — statistical analysis plan, NCT04512001. ClinicalTrials.gov document archive. (States the SDAI and CDAI definitions, the CRP unit as mg/dL, both full cut-off sets and the ACR response definition.)
  4. Aletaha D, Smolen J. The Simplified Disease Activity Index (SDAI) and the Clinical Disease Activity Index (CDAI): a review of their usefulness and validity in rheumatoid arthritis. Clin Exp Rheumatol. 2005;23(5 Suppl 39):S100–8.
  5. A study of LY3462817 in participants with rheumatoid arthritis — protocol, NCT04634253. ClinicalTrials.gov document archive. (Independently corroborates SDAI ≤ 3.3 and ≤ 11, CDAI ≤ 2.8, and states the SDAI CRP input range as 0.1 to 10.0 mg/dL.)

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