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. 2021 Oct 28;11(11):2003.
doi: 10.3390/diagnostics11112003.

Role of C-Reactive Protein in Discrimination between Transudative and Exudative Pleural Effusions

Yana Kogan  1   2   3 , Edmond Sabo  3   4 , Majed Odeh  1   3
Affiliations

Role of C-Reactive Protein in Discrimination between Transudative and Exudative Pleural Effusions

Yana Kogan et al. Diagnostics (Basel). .

Abstract

Background: There is still no wide agreement regarding the efficacy of the serum levels of C-reactive protein (CRPs), pleural fluid levels of CRP (CRPpf), and their ratio (CRPr) in the discrimination between transudative (Tr) and exudative (Ex) pleural effusions (PEs). Most of the previous studies were conducted on small cohorts, and the role of CRPs in the CRPpf gradient (CRPg) in this discrimination has not been previously reported. The present study aims to assess the diagnostic efficacy of CRPs, CRPpf, CRPg, and CRPr in the discrimination between TrPE and ExPE in a relatively large cohort of patients with PE.

Methods: The study population included 492 patients with PE, 210 of them with TrPE and 282 with ExPE. The levels of CRPs and CRPpf were measured, and the CRPg and CRPr were calculated. The values are presented as mean ± SD.

Results: The mean levels of CRPs, CRPpf, CRPg, and CRPr of the TrPEs were 11.3 ± 5.7 mg/L, 4.6 ± 2.8 mg/L, 6.7 ± 3.9 mg/L, and 0.40 ± 0.14, respectively, and for the ExPEs, they were 140.5 ± 112.8 mg/L, 52.8 ± 53.2 mg/L, 87.2 ± 72.4 mg/L, and 0.37 ± 0.15, respectively. The levels of CRPs, CRPpf, and CRPg were significantly higher in the ExPEs than in the TrPEs (p < 0.0001). No significant difference was found between the two groups for the levels of CRPr (p = 0.15). The best cut-off value calculated by the receiver operating characteristic (ROC) analysis for discriminating TrPE from ExPE was for CRPs, 20.5 mg/L with area under the curve (AUC) = 97% and p < 0.0001; for CRPpf, 9.9 mg/L with AUC = 95% and p < 0.0001; and for CRPg, 13.6 mg/L with AUC = 96% and p < 0.0001.

Conclusion: CRPs, CRPpf, and CRPg are strong markers for discrimination between TrPE and ExPE, while CRPr has no role in this discrimination.

Keywords: C-reactive protein; exudate; pleural effusion; transudate.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Serum CRP (CRPs) levels and their means for transudate group (11.3 mg/L) and exudate group (140.5 md/L), and best cut-off value (20.5 mg/L) for discrimination between the two groups. For both parameters p < 0.0001.
Figure 2
Figure 2
Pleural fluid CRP (CRPpf) levels and their means for transudate group (4.6 mg/L) and exudate group (52.8 mg/L), and best cut-off value (9.9 mg/L) for discrimination between the two groups. For both parameters p < 0.0001.
Figure 3
Figure 3
Serum and pleural fluid CRP gradient (CRPg) levels and their means for transudate group (6.7 mg/L) and exudate group (87.2 mg/L), and best cut-off value (13.6 mg/L) for discrimination between the two groups. For both parameters p < 0.0001.
Figure 4
Figure 4
Pleural fluid to serum CRP ratio (CRPr) levels and their means for transudate group (4.0) and exudate group (0.37). No significant difference was found between the two groups (p = 0.15).
Figure 5
Figure 5
Receiver operating characteristic (ROC) curve of best cut-off value of serum CRP (CRPs), and its statistical characteristics, for discrimination between transudative pleural effusion and exudative pleural effusion. CRPs best cut-off value = 20.5 mg/L, AUC = 97% (95% CI: 95.2–98.2), sensitivity = 93.3%, specificity = 93.0%, total accuracy = 93.1%, PPV = 93.3%, NPV = 93%, odds ratio = 179.9 (risk for exudate when CRPs value > 20.5 mg/L), p < 0.0001.
Figure 6
Figure 6
ROC curve of best cut-off value of pleural fluid CRP (CRPpf), and its statistical characteristics, for discrimination between transudative pleural effusion and exudative pleural effusion. CRPpf best cut-off value = 9.9 mg/L, AUC = 95% (95% CI: 92.9–96.5), sensitivity = 85.1%, specificity = 93.3%, total accuracy = 89%, PPV = 94%, NPV = 80%, odds ratio = 80 (risk for exudate when CRPpf value > 9.9 mg/L), p < 0.0001.
Figure 7
Figure 7
ROC curve of best cut-off value of serum and pleural fluid CRP gradient (CRPg), and its statistical characteristics, for discrimination between transudative pleural effusion and exudative pleural effusion. CRPg best cut-off value = 13.6 mg/L, AUC = 96.1% (95% CI: 94.4–97.7), sensitivity = 90%, specificity = 96%, total accuracy = 92%, PPV = 97%, NPV = 88%, odds ratio = 202.6 (risk for exudate when CRPg value > 13.6 mg/L), p < 0.0001.
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