Background Previous studies revealed conflicting results regarding the role of procalcitonin in predicting infections in patients with systemic lupus erythematosus (SLE).
Objectives This retrospective study aimed to analyse the role of procalcitonin (PCT) and C-reactive protein (CRP) in predicting infections in SLE patients, and to determine an optimal cut-off value for PCT and CRP for defining sepsis.
Methods This study was carried out in one single tertiary centre. Adult patients (>18-year-old) with underlying SLE who were admitted to hospital between 1st Jan 2007 and 31st Dec 2015 were included. Demographic data, PCT and CRP upon admission, and other clinical parameters were obtained. Infection was defined by positive culture, or based on clinical and radiological evidence with subsequent response to antimicrobial treatments. Active SLE disease activity was defined by SLEDAI, and also by SLE-related manifestations not included in SLEDAI. Mann-Whitney test was used to test the difference between numerical parameters between patients with and without infection. Spearman's correlation was used to analyse the correlation between PCT and CRP. Receiver operating characteristic (ROC) curves were plotted to define an optimal cut-off values for PCT and CRP in infection.
Results 33 (27 female & 6 male) SLE patients were included. Both mean and median age were 42-year-old. Among the 21 septic patients, 9 had active lupus and 12 had inactive disease. All but one of the 12 non-septic patients had active lupus. All 4 patients with underlying renal failure belonged to the infection group. There were 13 and 3 patients on immunosuppressive treatments in infection and non-infection groups respectively.
In patients with infection, mean PCT was 5.74ng/ml and mean CRP was 77.22mg/L. In those without, these were 0.29ng/ml and 20.04mg/L respectively. Both PCT (p=0.014) and CRP (p=0.016) levels were significantly higher in patients with infection than those without. There was no significant difference between the PCT and CRP levels in both septic patients (PCT p=0.862, CRP p=0.247) and non-septic patients (PCT p=1.000, CRP p=0.500) regardless of their SLE disease activity.
PCT level correlated positively with CRP level (r=0.456, p=0.008), but it had no correlation with age (p=0.978), gender (p=0.424), underlying renal failure (p=0.304), steroid (p=0.053) or other immunosuppressants (p=0.132) use.
ROC curves of PCT and CRP showed a similar area under curve (AUC) of 0.756 and 0.752 respectively. The cut-off for PCT was 0.78ng/ml (sensitivity 61.9%, specificity 91.7%), giving a positive predictive value (PPV) of 92.9%. The cut-off for CRP was 9.35mg/l (sensitivity 85.7%, specificity 66.7%), giving a PPV of 81.8%. Combining both PCT and CRP above their cut-offs, the specificity of predicting infection improved to 100% but the sensitivity worsened to 52%.
Conclusions Both PCT and CRP were useful in predicting infection SLE patients regardless of their disease activity. The cut-off of PCT at 0.78ng/ml and CRP at 9.35mg/l gave satisfactory positive predictive value for infection.
Lupus 2011; 20:125–130.
Clin Rheumatol 2014; 33:1209–1215.
Disclosure of Interest None declared