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Patient Activity Scale (PAS) for Rheumatoid Arthritis

Original composite patient-reported RA disease activity scale using HAQ disability index, pain, and global assessment

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Why use it

The PAS offers the same clinical utility as PAS II but uses the full HAQ disability index, which may be preferred in research settings, academic centers, or registries where the complete 20-item HAQ data are already being collected. The full HAQ provides more granular functional data across eight functional categories (dressing, arising, eating, walking, hygiene, reach, grip, activities), each rated across multiple sub-items. In most routine clinical practice, PAS II is preferred due to the efficiency of the 8-item HAQ-II; however, PAS remains the standard when full HAQ data are available.

About

The Patient Activity Scale (PAS) is the original version of the patient-reported composite disease activity measure for rheumatoid arthritis (RA), developed by Wolfe and Michaud and published in 2005. The PAS uses the same formula structure as the PAS II but incorporates the full HAQ (Health Assessment Questionnaire) disability index — a validated 20-item functional disability measure — rather than the abbreviated 8-item HAQ-II used in PAS II. Like PAS II, the PAS is entirely patient-reported, correlates well with DAS28-ESR (r=0.72), and produces a composite score from 0 to 10 based on three components: pain VAS (0–10), HAQ disability index (0–3), and patient global assessment VAS (0–10). The PAS was one of the first validated patient-reported composite RA disease activity measures and led directly to the development of the PAS II (which uses the shorter HAQ-II for greater clinical efficiency). Both tools are endorsed by the American College of Rheumatology (ACR) for clinical practice use and quality reporting in RA.

When to use

  • RA clinic visits when full HAQ data are routinely collected (e.g., academic centers or registries that use the 20-item HAQ)
  • Research settings requiring the original PAS as defined in the Wolfe 2005 validation
  • Cross-referencing with historical PAS data in clinical registries
  • Baseline documentation before initiating or changing DMARD therapy when full HAQ is available
  • For most routine clinical purposes, PAS II (8-item HAQ-II) is preferred for efficiency

Formula

PAS Calculation: Step 1: HAQ Disability Index (full 20-item HAQ) — 8 categories (dressing, arising, eating, walking, hygiene, reach, grip, activities) — Each category scored 0–3 (0=no difficulty; 3=unable) — If aids/devices or help from another person are used: category minimum = 2 — HAQ = mean of all 8 category scores (range 0–3) Step 2: PAS Formula PAS = (Pain VAS [0–10] + Patient Global VAS [0–10] + HAQ×3.33) / 3 Total range: 0–10 Thresholds: 0–0.25: Remission 0.26–3.7: Low disease activity (LDA) 3.71–7.99: Moderate disease activity (MDA) ≥8: High disease activity (HDA)

Pearls & pitfalls

  • The PAS and PAS II use the same formula and thresholds but differ in their HAQ component — PAS uses the full 20-item HAQ (scored 0–3), while PAS II uses the 8-item HAQ-II (scored 0–3).
  • The HAQ disability index for PAS is computed as the mean of 8 functional category scores (not 20 items directly) — each category uses the highest item score within it, and if an aid/device or help from another person is used, the minimum score for that category is 2.
  • The PAS thresholds are the same as PAS II: remission ≤0.25; LDA 0.26–3.70; MDA 3.71–7.99; HDA ≥8.0.
  • For most clinical settings, PAS II is preferred over PAS because the HAQ-II takes less time and yields equivalent results — use PAS only if the full HAQ is already being collected.
  • PAS correlates with CDAI (r=0.73), SDAI (r=0.71), and DAS28-ESR (r=0.72) in validation studies, confirming its convergent validity with examiner-based measures.

Next steps

PAS 0–0.25 (Remission): Maintain current therapy. Discuss taper if sustained ≥6 months. PAS 0.26–3.7 (Low Disease Activity): Continue current DMARD. Consider taper if sustained LDA ≥6 months. PAS 3.71–7.99 (Moderate Disease Activity): Optimize therapy; add or switch biologic/JAKi if inadequate response at 3–6 months. PAS ≥8 (High Disease Activity): Urgent therapy escalation; switch biologic mechanism if already on biologic; rheumatologist review within 4–6 weeks.

Evidence

Wolfe F, Michaud K. The Patient Activity Scale (PAS) and Patient Activity Scale-II (PAS-II): compared with composite disease activity measures in rheumatoid arthritis patients. Arthritis Rheum. 2005;52(3):657-666. PMID:15751062. PAS validation in National Data Bank for Rheumatic Diseases (NDB) cohort. Endorsed by ACR for quality reporting in rheumatoid arthritis.

References

  1. Wolfe F, Michaud K. The Patient Activity Scale (PAS) and Patient Activity Scale-II (PAS-II): compared with composite disease activity measures in RA. Arthritis Rheum. 2005;52(3):657-666. — link
  2. Fries JF et al. Measurement of patient outcome in arthritis. Arthritis Rheum. 1980;23(2):137-145. — link
  3. Anderson J et al. Rheumatoid arthritis disease activity measures: ACR recommendations for use in clinical practice. Arthritis Care Res. 2012;64(5):640-647. — link