Increased concentrations of the soluble mannose receptor in serum from patients with pneumococcal bacteraemia, and prediction of survival.

Background: The soluble mannose receptor (sMR) is a new serum marker of macrophage activation. The aim of the present study was to investigate sMR as a prognostic marker in patients with invasive pneumococcal disease (IPD), and compare it to other inflammatory biomarkers.

Methods: Samples from 128 patients with IPD were collected at the time of first positive blood culture and analysed using an in-house sMR assay. Clinical data were retrieved from patient files. The main outcome investigated was in-hospital mortality.

Results: The median sMR concentration in the entire group of patients was 0.77 mg/L. There was a significant difference in sMR concentration between patients below (n = 92, sMR = 0.82 mg/L) or above (n = 36, sMR = 0.73 mg/L) the age of 75 (p < 0.001). In the entire group there was a significant difference in sMR concentrations between survivors (n = 107, sMR = 0.72 mg/L) and non-survivors (n = 21, sMR = 1.38 mg/L), but for patients 75 years or older this difference was not statistically significant. For prediction of survival sMR seemed most promising (area under the receiver operating characteristic curve (AUC) = 0.79) compared with sCD163 (AUC = 0.70) and CRP (AUC = 0.73). In patients 75 years or older the AUC was lower for all three markers (sMR = 0.56, sCD163 = 0.38, CRP = 0.66).

Conclusions: The results of this study designate sMR as a potential new biomarker in infectious disease. Additionally, it emphasizes the importance of research into macrophage malfunction in elderly patients.