To evaluate and compare the clinical implications of common inflammatory markers in systemic rheumatic diseases (SRDs).
We investigated the profiles of erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) and white blood cell (WBC) count in treatment-naïve patients with SRDs, osteoarthritis and pneumonia diagnosed at Seoul National University Hospital during 2004-2016. SRDs included rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), ankylosing spondylitis (AS), systemic sclerosis (SSc), idiopathic inflammatory myopathy (IIM) and adult-onset Still's disease (AOSD). Associations between inflammatory markers were evaluated using Pearson's correlation and regression analysis. ROC curve analysis was performed to examine the predictive value of inflammatory markers for SRD diagnosis.
We identified a total of 1191 patients. Leukocytosis was present in < 20% SRD patients. There was marked variability in ESR and CRP levels among different SRDs. The highest mean CRP levels (mean ± SD, mg/dL) were observed in AOSD (11.3 ± 7.9), followed by RA (2.0 ± 3.3), IIM (1.8 ± 3.5), SLE (1.5 ± 3.1), SSc (0.6 ± 1.3) and AS (0.08 ± 0.1). Mean ESR (mm/h) was also highest in AOSD (71.2 ± 31.0), followed by SLE (47.3 ± 34.2), RA (45.5 ± 30.6), IIM (40.8 ± 24.8) and SSc (27.8 ± 26.0). All SRDs showed significant positive correlations between ESR and CRP: greatest in RA (r = 0.53, p < 0.001) and weakest in SLE (r = 0.20, p = 0.03). WBC correlated weakly with CRP but not with ESR in most SRDs. While the AUC for WBC count was less than that of ESR or CRP, the AUC for ESR and CRP were similar in SRD. The optimal cuff-off values for inflammatory markers predicting SRD were within or slightly above the normal limit.
ESR, CRP and WBC are not always elevated in treatment-naïve patients with SRD. Individual SRDs have a unique profile of inflammatory markers. However, routine inflammatory markers should still be interpreted with caution when diagnosing and assessing disease activity in those with SRD. Key Points •Leukocytosis and elevation of ESR and CRP are not always present in all systemic rheumatic diseases. •Inflammatory markers are often dissociated and they are not specific for disease diagnosis. •Better biomarkers, which measure disease-specific local and systemic inflammation, are needed.