Sensitivity of 40.91% and specificity of 100.0% were recorded for the presence of infection in febrile SLE patients when the cut-off values of <1.2447 and >4.67 were applied to the C4d/CR1 ratio and serum CRP level, respectively (Table 4, Figure 3); similarly, sensitivity of 80% and specificity of 100% were noted for cut-off values of >1.2447 and <2.2, respectively, for the absence of infection in febrile SLE patients (Table 5, Figure 3). Here, CRP is linked to systemic lupus erythematosus.