Diagnostic value of CRP/Albumin-globulin ratio and monocyte-to-lymphocyte ratio in differentiating parapneumonic effusion types

N.A. Yetkin, F.M. Simsek, B. Baran, B. Rabahoglu, N. Tutar, İ. Gulmez

Department of Pulmonology, Faculty of Medicine, Erciyes University, Kayseri, Turkiye. nuryetkin@erciyes.edu.tr 

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• Respiratory Medicine

OBJECTIVE: Parapneumonic effusion (PPE), a pneumonia-related complication, can progress to complicated PPE (CPPE) and often requires invasive treatment. Although early differentiation is essential, the diagnostic role of hematological inflammatory markers remains unclear. This study evaluated hematological inflammatory markers to distinguish between pleural effusion types, particularly CPPE and uncomplicated PPE (uCPPE), in order to identify the most reliable biomarkers. 

MATERIALS AND METHODS: This retrospective study analyzed 94 cases of pleural effusion classified as transudative, malignant, tuberculous, or PPE. PPE was further divided into CPPE and uCPPE. C-reactive protein (CRP) and procalcitonin (PCT) levels, systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), CRP/albumin-globulin ratio (CAGR), albumin-globulin ratio (AGR), neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), and platelet-lymphocyte ratio (PLR) were analyzed. Receiver Operating Characteristic (ROC) curve analysis was used to determine the diagnostic accuracy via the area under the curve (AUC) and optimal cut-off values. 

RESULTS: Inflammatory markers effectively differentiated pleural effusion types, with CAGR showing the highest accuracy for PPE diagnosis (AUC, 0.866; cut-off: 13.75; sensitivity = 93.8%, specificity = 51.1%). Among the CPPE and uCPPE markers, MLR demonstrated the best performance (AUC: 0.707; cut-off: 3.615; sensitivity: 87.5%; specificity: 77.8%), followed by NLR (AUC: 0.702) and PLR (AUC: 0.704), whereas SIRI and SII had modest utility. Although MLR showed superior accuracy, the addition of SII improved the sensitivity. 

CONCLUSIONS: This study demonstrates that among hematological markers, CAGR is the most accurate for diagnosing PPE, while MLR best distinguishes CPPE from uCPPE. However, the limited specificity of CAGR highlights the need for the combined use of biomarkers. Prospective multicenter studies are warranted to validate and refine these findings. 

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