Immune Cell-Based versus Albumin-Based Ratios as Outcome Predictors in Critically Ill COVID-19 Patients

Purpose: The aim of the retrospective, single-center study was to assess the prognostic value of immune cell-based and albumin-based ratios regarding lethal outcome in critically ill COVID-19 patients.

Patients and methods: We analyzed 612 adult critically ill COVID-19 patients admitted to the intensive care unit (ICU) between April 2020 and November 2022. Blood measurement on admission to the ICU encompassed complete blood count (CBC), IL-6, C-reactive protein (CRP), albumin, lactate, lactate dehydrogenase (LDH), serum bicarbonate, arterial base deficit/excess (BD/E), and D-dimer. All the measured and calculated parameters were compared between survivors and nonsurvivors, with the outcome measure being hospital mortality.

Results: Immune cell-based ratios [NLR - Neutrophil-to-Lymphocyte Ratio, MLR - Monocyte-to-Lymphocyte Ratio, PLR - Platelet-to-Lymphocyte Ratio, MPV - Mean Platelet Volume, MPV/PC - Mean Platelet Volume-to-Platelet Count Ratio, Derived (d-)NLR ratio - neutrophil count divided by the result of white blood cell (WBC) count - neutrophil count), N/LP - Neutrophil count x 100/Lymphocyte count x Platelet count, CLR - C-reactive protein (CRP)-to-Lymphocyte Ratio, CPR - CRP-to-Platelet Ratio, LLR - Lactate dehydrogenase (LDH)-to-Lymphocyte Ratio, Systemic Immune Inflammation Index (SII) - platelet x neutrophil/lymphocyte count, Systemic Inflammation Response Index (SIRI) - neutrophil x monocyte/lymphocyte count] were investigated. White blood cell and neutrophil counts were significantly higher, while lymphocyte and platelet counts were significantly lower in nonsurvivors. MPV, MPV/PC, NLR, d-NLR, MLR, N/LP, CRP, LDH, CPR, CLR, LLR, SII, and SIRI values were significantly higher in nonsurvivors. Monocyte count and PLR values did not differ significantly between groups. Albumin-based ratios included CRP-to-Albumin Ratio (CAR), Lactate-to-Albumin Ratio (LAR) and LDH-to-Albumin Ratio (LDH/ALB). All values were significantly higher in nonsurvivors.

Conclusion: The only independent predictor of lethal outcomes at ICU admission is the albumin-based LDH/ALB ratio. Most of the other parameters were moderate, although highly significant predictors of mortality in critically ill COVID-19 patients.