ORIGINAL ARTICLE Comparison of the DAS28-CRP and DAS28-ESR in patients with rheumatoid arthritis Ilker SENGUL, Seniz AKCAY-YALBUZDAG, Bugra INCE, Altinay GOKSEL-KARATEPE and Taciser KAYA Department of Physical Medicine and Rehabilitation, Izmir Bozyaka Training and Research Hospital, Izmir, Turkey Abstract Aim: To compare the Disease Activity Score with 28 joint (DAS28) using erythrocyte sedimentation rate (ESR) (DAS28-ESR) and DAS28 using C-reactive protein (CRP) (DAS28-CRP) with thresholds validated for DAS28- ESR in Turkish patients with rheumatoid arthritis. Method: The DAS28 data of 112 patients with rheumatoid arthritis followed in a local outpatient clinic were used. First, the correlation between DAS28-CRP and DAS28-ESR and the correlation between their unique com- ponents ([0.36 9 In (CRP + 1) + 0.96] and [0.70 9 In (ESR)]) were analyzed. Second, a Bland–Altman plot was constructed for the evaluation of the level of agreement between DAS28-CRP and DAS28-ESR. Lastly, the agreement between these two methods was analyzed by j coefficient. Results: Although there was a strong correlation between DAS28-CRP and DAS28-ESR, the correlation between their unique components was fair. Although more than 95% of the point data fall between the upper and lower bounds of the limit of agreement, the percentage error (46%) was higher than the acceptable proportion of 30%. The j coefficient of agreement between DAS28- ESR and DAS28-CRP with validated thresholds for DAS28-ESR was 0.42, which was close to the lower boundary for moderate agreement. Conclusion: The results of this study demonstrated that there is discordance between DAS28-ESR and DAS28- CRP with the validated thresholds for DAS28-ESR. Using the DAS28-CRP with threshold values validated for DAS28-ESR may lead to errors in the determination of disease activity and therefore may lead to errors in the management of patients with rheumatoid arthritis. Key words: C-reactive protein, DAS28, erythrocyte sedimentation rate, rheumatoid arthritis. INTRODUCTION The original Disease Activity Score with 28 joints (DAS28) criterion, developed in 1995, is composed of four components, including the number of swollen joints, number of tender joints, patient’s global health score and erythrocyte sedimentation rate (ESR). The validated threshold values of DAS28 using ESR (DAS28-ESR) are 2.6 for remission, 3.2 for low disease activity and 5.1 for high disease activity.1 In 2004, Fransen et al.2 suggested DAS28 using C- reactive protein (CRP) (DAS28-CRP) instead of DAS28-ESR with the same thresholds validated for DAS28-ESR. The primary reasons underlying this sug- gestion were as follows: ESR is under the influence of several factors, such as age, sex, anemia and plasma proteins,3 and CRP is more sensitive to short-time changes in inflammation.4 In several countries, Correspondence: Dr. Ilker Sengul, MD, Specialist in Physical Medicine and Rehabilitation, Department of Physical Medi- cine and Rehabilitation, Izmir Bozyaka Training and Research Hospital, Saim Cıkrıkcı Caddesi, No: 59, Karabaglar, Izmir, Turkey. Email: ilkrsngl@gmail.com © 2015 Asia Pacific League of Associations for Rheumatology and Wiley Publishing Asia Pty Ltd International Journal of Rheumatic Diseases 2015; 18: 640–645 http://crossmark.crossref.org/dialog/?doi=10.1111%2F1756-185X.12695&domain=pdf&date_stamp=2015-05-27 DAS28 cutoff values are being used for indicating the initiation and maintenance of biological agents and determining the response to treatment. There is no cer- tainty regarding which DAS28 index should be used. In the last 10 years, there has been debate regarding whether these two indexes can be used interchangeably. In contrast to the results obtained by Fransen et al.,2 subsequent studies have demonstrated that DAS28-CRP underestimates disease activity and overestimates response to treatment.5–11 The characteristics of the study populations may be responsible for the magnitude of discrepancy between DAS28-CRP and DAS28-ESR.6,7 As far as we know, there have not been any studies comparing DAS28-CRP and DAS28-ESR in the Turkish rheumatoid arthritis (RA) population. In this study, our aim was to evaluate the agreement between DAS28- CRP and DAS28-ESR in a group of patients with RA who were followed-up in our outpatient clinic. METHODS This study was approved by the Ethics Committee of Izmir Bozyaka Training and Research Hospital. Patients with RA who received at least one synthetic or biologi- cal disease-modifying anti-rheumatic drug (DMARD) for at least 3 months were included in the analysis. The DAS28 data calculated at a single point in time were used. Patients with any evidence of any infectious dis- ease in the last month prior to data collection were excluded from the analysis. Patients with a history of malignancy and secondary Sj€ogren’s syndrome were also excluded from the analysis because of their ten- dency to have high rheumatoid factor (RF) values that might contribute to ESR elevation. CRP values, as deter- mined by the nephelometric method, were used in the calculation of DAS28-CRP, and ESR values, as deter- mined by the Westergren method, were used in the cal- culation of DAS28-ESR. DAS28-CRPs (DAS28-CRP with thresholds validated for DAS28-ESR and DAS28-CRP with thresholds pro- posed by Fleischmann et al.6) and DAS28-ESR were compared. The unique component of DAS28-CRP (0.36 9 In [CRP + 1] + 0.96) and unique component of DAS28-ESR (0.70 9 In [ESR]) were also compared. The analyses were performed using the IBM SPSS Statistics for Windows version 21.0 (IBM Corp., Armonk, NY, USA) and MedCalc Statistical Software version 13 (Medcalc Software bvba, Ostend, Belgium). First, whether the numerical data conformed to a nor- mal distribution was assessed by Kolmogorov–Smirnov test. Descriptive statistics were then calculated for the patients. The relationships between DAS28-ESR and DAS28-CRP with the validated thresholds for DAS28- ESR and between their unique components were ana- lyzed with correlation coefficients. Bland–Altman plots were also established for the evaluation of variation and level of agreement between DAS28-ESR and DAS28- CRP with the validated thresholds for DAS28-ESR. The agreement between the DAS28-ESR and each DAS28- CRP threshold (DAS28-CRP with validated thresholds for DAS28-ESR, DAS28-CRP with thresholds proposed by Fleiscmann et al.6) were analyzed by j coefficient. RESULTS Data from 112 patients with RA were used for analysis. The numeric variables were not normally distributed, except for age, DAS28-ESR and DAS28-CRP. The mean age of patients was 55 � 12.4 years, the majority of patients were female, and the proportion of RF positiv- ity was 77%. Disease duration was median (range) 108 (3–480) months. A total of 72% of patients were being treated with methotrexate, 34% were being treated with leflunomide, 9% were being treated with sulfasalazine, 5% were treated with hydroxychloroquine, 14% were being treated with biologic DMARDS (tumor necrosis factor [TNF]-alpha blockers), and 54% of patients were being treated with glucocorticoids (Table 1). Table 1 Patients’ demographic and clinical characteristics Age, years (mean � SD) 55.0 � 12.4 Female gender, n (%) 100/12 (89.3) Disease duration, months, median (min, max) 108 (3, 480) RF (%) 77 TJC, number, median (min, max) 2 (0, 28) SJC, number, median (min, max) 0 (0, 19) VAS-GH, median (min, max) 30.5 (0, 100) ESR, mm/h, median (min, max) 28 (2, 97) CRP, mg/L, median (min, max) 7 (1, 79) DAS28-ESR, mean � SD 3.8 � 1.2 DAS28-CRP, mean � SD 3.2 � 1.2 Methotrexate use, % 72 Leflunomide, % 34 Sulfasalazine, % 9 Hydroxychloroquine, % 5 Biologic DMARD use, % 14 Glucocorticoid use, % 54 RF, rheumatoid factor; min, minimum; max, maximum; TJC, tender joint count; SJC, swollen joint count; VAS, visual analogue scale; GH, global health; ESR, erythrocyte sedimentation rate; CRP, C-reactive protein; DAS28, Disease Activity Score based on 28 joint count; DMARD, disease-modifying antirheumatic drug. International Journal of Rheumatic Diseases 2015; 18: 640–645 641 Comparison of DAS28-CRP and DAS28-ESR 1756185x, 2015, 6, D ow nloaded from https://onlinelibrary.w iley.com /doi/10.1111/1756-185X .12695 by B ezm -I A lem V akif U niversity, W iley O nline L ibrary on [11/08/2025]. See the T erm s and C onditions (https://onlinelibrary.w iley.com /term s-and-conditions) on W iley O nline L ibrary for rules of use; O A articles are governed by the applicable C reative C om m ons L icense Whereas DAS28-ESR and DAS28-CRP (with validated thresholds for DAS28-ESR) were highly correlated (Pearson’s correlation coefficient, 0.93; P < 0.001), the scatter diagram with the line of equality showed some disagreement (Fig. 1). The correlation between their unique components was not as highly correlated (Spearman’s correlation coefficient, 0.44; P < 0.001) (Fig. 2) as those between DAS28-CRP and DAS28-ESR. The normality test of the differences, conducted by the Kolmogorov–Smirnov test, showed that the sample distribution of differences was normal (P = 0.086) (Fig. 3). In the Bland–Altman analysis, 3.6% (4/112) of the data points were outliers, and three of four fell out- side the upper limit of the agreement. The mean differ- ence (bias) between DAS28-ESR and DAS28-CRP was �0.6 � 0.45 (P < 0.0001, 95% CI = �0.52, �0.69). The DAS28-CRP method had a negative bias, and yielded a lower disease activity than that measured simultaneously with the DAS28-ESR method (Fig. 4). The precision was 0.88 (95% CI = �1.48–0.28) and percentage error was 46%. The j coefficient of agreement between DAS28-CRP with thresholds validated for DAS28-ESR and DAS28- ESR was 0.42. The j coefficient increased to 0.56 when Figure 1 Scatter diagram with the line of equality of DAS28- CRP and DAS28-ESR. The disease activity values obtained with DAS28-CRP is strongly correlated with the disease activity val- ues obtained with DAS28-ESR, but the scatter diagram indi- cates a degree of disagreement. Figure 2 Scatter diagram with the line of equality of DAS28- CRP and DAS28-ESR. The figure shows that the unique com- ponent of DAS28-ESR is not equal to the unique component of DAS28-CRP in the majority of patients. The correlation between the unique components is also not strong as those between DAS28-ESR and DAS28-CRP. Figure 3 The histogram of the difference scores. The differ- ence in scores was distributed normally around the bias of �0.60. Figure 4 Bland–Altman plot of DAS28-CRP and DAS28-ESR. The x-axis represents the average disease activity obtained with te DAS28-ESR and DAS28-CRP. The y-axis represents the dif- ference in disease activity measured with DAS28-ESR and DAS28-CRP. The solid horizontal line represents the mean difference, which is reported as the bias. The dashed hori- zontal lines represent the 95% confidence limits (limits of agreement). 642 International Journal of Rheumatic Diseases 2015; 18: 640–645 I. Sengul et al. 1756185x, 2015, 6, D ow nloaded from https://onlinelibrary.w iley.com /doi/10.1111/1756-185X .12695 by B ezm -I A lem V akif U niversity, W iley O nline L ibrary on [11/08/2025]. See the T erm s and C onditions (https://onlinelibrary.w iley.com /term s-and-conditions) on W iley O nline L ibrary for rules of use; O A articles are governed by the applicable C reative C om m ons L icense DAS28-CRP with thresholds proposed by Fleischman et al.6 were used. The proportion of agreement (Pa) also increased to 76.8% with DAS28-CRP with thresholds proposed by Fleischmann et al.6, which was 59.8% with DAS28-CRP with thresholds validated for DAS28-ESR (Table 2). DISCUSSION DAS28-CRP with validated thresholds for DAS28-ESR was demonstrated to be a validated tool for determin- ing functional and radiographic progression. Recent studies investigating the agreement between DAS28- ESR and DAS28-CRP revealed that DAS28-CRP had a tendency to underestimate disease activity and to over- estimate response to treatment. The results of our study also demonstrated that these two indexes were not equivalent. In this study, we hypothesized that DAS28-CRP and DAS28-ESR could not be used interchangeably. As observed in the discrepancy between the correlation analysis and scatter diagram, a strong correlation does not always mean agreement between two methods.12 The subjective patient global evaluations in DAS28 may result in greater disease activity scores.13,14 Therefore, studying the relationship between the unique compo- nents of the indexes may be more suitable than assess- ing the relationship between DAS28-ESR and DAS28- CRP.6 In this study, the correlation between their unique components was only moderate. The fair corre- lation between the unique components of these two indexes was consistent with the results of the study by Fleiscmann et al.6 Although 96.4% of the point data were between the upper and lower limits of agreement, the percentage error of 46% was higher than the upper limit (30%).15 In other words, these two methods, which measured the same parameters, were not equivalent in this study population. Although some solutions, including estimating new thresholds corresponding to thresholds of DAS28-ESR5– 8 and amending the formulation of DAS28-CRP,10,11 have been suggested for overcoming the discrepancy between DAS28-ESR and DAS28-CRP, so far, indepen- dent, validated threshold values for DAS28-CRP have not been determined.6 Because assessing the entire population is difficult, the existing determined thresholds for DAS28-CRP5,7 are restricted to limited populations or ethnic groups. As developing a universal formula is unlikely, Gaujoux- Viala et al.8 suggested the development of formulas specific to ethnic or social origin. The study by Fleisch- mann et al.6 is critical in this respect because it is the largest comparative analysis of DAS28-CRP and DAS28- ESR ever made. They compared DAS28-CRP and DAS28-ESR using three different RA patient popula- tions across five randomized controlled trials across multiple geographic regions (Europe, Asia, North Amer- ica, Latin America, Australia). However, only thresholds for remission and low disease activity were determined because there were not enough numbers of patients in the moderate and high disease activity categories. Another advantage of the study by Fleischmann et al.6 was that they obtained the cut-offs corresponding to DAS28-ESR remission and low disease activity by three diverse approaches, including cumulative distribution plots, receiver operating characteristic (ROC) curves and maximum concordonce. Soon after the study by Fleischmann et al.6 was published online, Favalli et al.16 studied the validation of the DAS28-CRP thresh- olds proposed by Fleischman et al.6 for remission and low disease activity in 562 patients with rheumatoid arthritis who were receiving biologic therapy. They reported that discordance between the DAS28-CRP and DAS28-ESR decreased when the thresholds proposed by Fleischmann et al.6 were used. However, validation studies with the thresholds proposed by Fleischman et al.6 are needed for functional and radiographic pro- gression. In this study, the j coefficient only increased to 0.56, which is close to the upper boundary of moder- ate agreement. Table 2 Agreement between the DAS28-ESR and DAS28-CRP DAS28-ESR DAS28-CRP1 DAS28-CRP2 n (%) n (%) n (%) Remission 16 (14) 36 (32) 29 (26) LDA 19 (17) 20 (18) 16 (14) MDA 59 (53) 46 (41) – HDA 18 (16) 10 (9) – MDA + HDA 77 (69) – 67 (60) 112 (100) 112 (100) 112 (100) j coefficient DAS28-ESR – 0.42 0.56 Pa DAS28-ESR, % – 59.8 76.8 DAS28-ESR, Disease Activity Score in 28 joints calculated with erythro- cyte sedimentation rate; DAS28-CRP1, Disease Activity Score in 28 joints calculated with C-reactive protein with thresholds validated for DAS28-ESR; DAS28-CRP2 Disease Activity Score in 28 joints calculated with C-reactive protein with thresholds (2.4 for remission; 2.9 for low disease activity) based on the study by Fleischmann et al.6; LDA, low disease activity; MDA, medium disease activity; HDA, high disease activity; Pa, proportion of agreement. International Journal of Rheumatic Diseases 2015; 18: 640–645 643 Comparison of DAS28-CRP and DAS28-ESR 1756185x, 2015, 6, D ow nloaded from https://onlinelibrary.w iley.com /doi/10.1111/1756-185X .12695 by B ezm -I A lem V akif U niversity, W iley O nline L ibrary on [11/08/2025]. See the T erm s and C onditions (https://onlinelibrary.w iley.com /term s-and-conditions) on W iley O nline L ibrary for rules of use; O A articles are governed by the applicable C reative C om m ons L icense The reasons why CRP is preferred instead ESR in eval- uating disease activity by DAS28 are as follows: CRP is a direct measurement marker of inflammation, more sen- sitive to changes in inflammation, less influenced by sex, age and plasma proteins, and may be standardized in a laboratory.3,4 On the other hand, the levels of CRP may also be influenced by smoking, elevated blood pressure, high body mass index, and abdominal adipos- ity.17,18 As such, CRP may increase in certain comorbid conditions, such as diabetes mellitus, hypertension, cor- onary heart disease and obesity and, to a lesser extent, in inflammatory or infectious diseases. These aspects of CRP should also be considered when evaluating disease activity and tailoring treatment. Baseline CRP levels and DAS28-CRP may also be affected by CRP gene polymorphisms and the individ- ual gene pool of various populations. As different threshold values were calculated in studies conducted in different populations, the characteristics of the study populations should be taken into consideration. For example, DAS28-CRP tends to be lower in Japa- nese.6 To our knowledge, no studies have been con- ducted on CRP gene polymorphisms in Turkish RA patients. Gender (in favor of women) and long disease dura- tion also contribute to the discrepancy between DAS28-ESR and DAS28-CRP.5 The proportion of females (89%) and disease duration (108 [3, 480] months) could have increased the mean DAS28-ESR scores in this study, and could have contributed the discrepancy. The influence of TNF-alpha blockers on CRP levels may increase the disagreement in results obtained using the two methods. This opinion was confirmed in the APEAL and LARA trials, in which the discordance pro- portions between DAS28-CRP and DAS28-ESR were found to be higher in the TNF-alpha blockers plus methotrexate groups. On the other hand, in the COMET and TEMPO studies, similar discordance pro- portions were found in both groups (etanercept plus methotrexate vs. methotrexate groups).6 In this study, 14% of the patients received biological DMARDs (TNF- alpha blockers) and the DAS28-CRP scores might have been influenced by the medication. There were several limitations in our study. The study population was too small, in comparison with the previous study that compared DAS28-CRP and DAS28-ESR, and therefore the results of our study can- not be generalized to the entire Turkish RA population. Long disease duration and female bias were also other factors that could have affected the DAS28-ESR score. Another limitation was that we did not investigate the other contributing factors that may have influenced CRP levels, such as metabolic syndrome. As stated pre- viously, the medication applied, specifically TNF-alpha blockers, might have also influenced DAS28-CRP scores. In our study, the proportion of use of TNF- alpha blocker was 14%, which might have partially influenced CRP levels. CONCLUSIONS The results of this study demonstrated that there is a disagreement between DAS28-ESR and DAS28-CRP with the validated thresholds for DAS28-ESR. There is a need for universally validated DAS28-CRP thresholds, but it is difficult to determine acceptable thresholds for DAS28-CRP because of the characteristics of individual societies. To use the same threshold values for both DAS28-ESR and DAS28-CRP may lead to partially incorrect determination of disease activity and, as such, may lead to erroneous treatment decisions. 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Cardio- vasc Res 66, 265–75. 18 Khera A, McGuire DK, Murphy SA et al. (2005) Race and gender differences in C-reactive protein levels. J Am Coll Cardiol 46, 464–9. International Journal of Rheumatic Diseases 2015; 18: 640–645 645 Comparison of DAS28-CRP and DAS28-ESR 1756185x, 2015, 6, D ow nloaded from https://onlinelibrary.w iley.com /doi/10.1111/1756-185X .12695 by B ezm -I A lem V akif U niversity, W iley O nline L ibrary on [11/08/2025]. See the T erm s and C onditions (https://onlinelibrary.w iley.com /term s-and-conditions) on W iley O nline L ibrary for rules of use; O A articles are governed by the applicable C reative C om m ons L icense