A total of 16026 articles were analysed by BIBOT, 948 were excluded on the basis of the language in which they were written, and 2221 were excluded on the basis of their publication date. Among the remaining articles, 2241 were selected based on their titles, abstracts and keywords (annex 1). These articles were then ranked in order of relevance by the program BIBOT. We automatically extracted 10 activity scores from references that met our inclusion criteria: DAS28 (ESR), DAS28 (CRP), CDAI, SDAI, ASDAS (ESR), ASDAS (CRP), the EULAR Sjögren's syndrome (SS) Disease Activity Index (ESSDAI), the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI-2K), Disease Activity in PSoriatic Arthritis (DAPSA), PMR-AS (ESR) and PMR-AS (CRP) (table 1). These activity scores cover 7 different pathologies in the field of rheumatology: RA, AS, Sjögren's syndrome (SjS), systemic lupus erythematosus (SLE), psoriatic arthritis (PsA) and PMR. Only a few scores in medical fields outside rheumatology may be adaptable for the AS135 scoring system (table 2).
DAS28 was mentioned in 1227 abstracts, SDAI was mentioned in 196 abstracts, and ASDAS-CRP was mentioned in 13 abstracts (Annex 2). Therefore, DAS 28 was the most frequently used activity criterion in RA, but two variants, DAS28-CRP (350 abstracts) and DAS28-ESR (269 abstracts), were also used. We compared their use in the literature from 2004 to 2018 to determine whether one of them became predominant in the literature. Although a tendency for the use of DAS28-CRP in 2013 and 2014 was observed, DAS28-CRP and DAS28-ESR were indiscriminately used over time, justifying that we include both in the AS135.
AS135 score equation
The AS135 score is defined as a universal activity score obtained by the linear interpolation of existing scores. Threshold values for low, moderate and high activity states were set at 1, 3 and 5, respectively, to reflect the range typically used for each activity state in existing activity scores: these scores generally separate into four groups such that remission exhibits the smallest interval, low and moderate activity exhibit quite similar intervals (for example, lower than 1.5 for PMR-AS), and high activity exhibits the greatest interval (for example, 17 to 50 for PMR-AS). These arbitrary thresholds are then associated with the thresholds for the existing scoring system, and an interpolation can be calculated. In this way, it is possible to compare the activity scores defined on different domains from different parameters by converting these scores into AS135 scores, which are defined on an intuitive scale: [0,10] (equation 1, table 3), where x is the value of the original score to be converted, while a and b are the nearest thresholds of x such that and .
Example of application of the AS135 in Rheumatoid Arthritis
To illustrate application of the AS135 score, consider the following hypothetical situation: two patients have RA, and their disease activities were calculated based on different information. The first patient, p1, has a DAS28 score of 6.7, while the second, p2 has an SDAI score of 25. Comparing the pathological activities in p1 and p2 does not seem to be a very intuitive task based on this information alone. The conversion of these scores to AS135 proceeds as follows: the equation of the conversion is set for patient p1 (equation 2, table 2), with the thresholds a = 5.2 and b = 9.1 defined for the DAS28 score, corresponding to the high activity threshold and maximum value adopted by the DAS28 score, respectively, and because by definition AS135(thresholdhigh) = 5 and AS135(thresholdmax) = 10, equation 2 can be expanded, and the value AS135(p1) can be calculated (equation 3, table 2). The same reasoning is used with patient p2 by adopting the values a = 11 and b = 26, corresponding to the thresholds of moderate and high activity by the SDAI score. Because by definition AS135(thresholdmoderate) = 3 and AS135(thresholdhigh) = 5, the equation for patient p2 can be written as equation 4 (table 2). Thus, we finally obtain the score AS135(p1) = 6.92 and score AS135(p2) = 4.8 defined on the same interval [0, 10]. Patient p1 is thus described as having high disease activity (since AS135(p1) > 5), and patient p2 is characterized by moderate activity (since 3 < AS135(p2)) < 5).
Example of association between AS135 and PMR-AS in polymyalgia rheumatica
Figure 3 shows in the Tenor study, which evaluated patients with polymyalgia rheumatica at different visits (9), the link between AS135 and PMR-AS. All patients are, as expected, classified similarly by the AS135 and the PMR-AS.