SUMMARY OBJECTIVE: Gamma-glutamyl transpeptidase-platelet ratio, system inflammation response index, and systemic immune inflammation index are three systemic immune and inflammation indexes that were investigated for their diagnostic and prognostic proficiencies in cardiovascular diseases and cancers. However, their predictive values for invasive aspergillosis have not yet been studied. The aim of this study was to evaluate Gamma-glutamyl transpeptidase-platelet ratio, system inflammation response index, and systemic immune inflammation index levels and their diagnostic values in invasive aspergillosis. METHODS: A total of 23 patients with invasive aspergillosis and 23 sex- and age-matched healthy participants were included in this study. Complete blood count parameters and liver function tests were studied. Gamma-glutamyl transpeptidase-platelet ratio, system inflammation response index, and systemic immune inflammation index were calculated. RESULTS: Leukocyte, neutrophil, lymphocyte, and monocyte levels were statistically significantly higher in IA group (p=0.031, p=0.027, p=0.033, and p=0.001, respectively). In invasive aspergillosis group, platelets were numerically lower; Aspartate transaminase, alanine aminotransferase, and lactic dehydrogenase levels were numerically higher than those in control group but differences between levels were not statistically significant (p>0.05). The γ-glutamyl transpeptidase levels of patients were statistically significantly higher (p=0.007), and in addition, statistically significant differences were found between groups in terms of gamma-glutamyl transpeptidase-platelet ratio, system inflammation response index, and systemic immune inflammation index (p<0.001, p=0.037, p=0.001, respectively). Receiver operating characteristic analysis was performed, and areas under the curves were evaluated. gamma-glutamyl transpeptidase-platelet ratio had the higher area under the curve than systemic immune inflammation index and system inflammation response index (AUC 0.849, 0.798, 0.693, respectively). The results from receiver operating characteristic analysis of the data suggested that the use of a cutoff value of 0.15 for gamma-glutamyl transpeptidase-platelet ratio would be optimum for clinical use to confirm independent predictors of patients with invasive aspergillosis. CONCLUSIONS: Gamma-glutamyl transpeptidase-platelet ratio is an independent, a useful predictor, and is superior to other evaluated markers in the diagnosis of inflammation in invasive aspergillosis. Gamma-glutamyl transpeptidase-platelet ratio may also be a helpful biomarker for clinicians to follow-up the inflammatory process of these patients.