Association of Anemia Severity with Distinct Microbial and Inflammatory Signatures in Patients Receiving Vancomycin

Background: Anemia is a pervasive public health issue that is both a risk factor and a consequence of infection. This study aims to determine the prevalence and correlates of anemia in adults receiving vancomycin (VAN). Methods: A retrospective cross-sectional analysis of clinical data was undertaken for 299 patients treated with VAN at a tertiary care hospital from January 2024 to February 2025. Subjects were stratified by anemia severity into non-anemic, mild, moderate, and severe groups. Frequency was examined using the chi-squared test, medians by Kruskal–Wallis test, monotonic relations by Spearman’s correlation, and independent predictors using regression models. Results: Anemia was extremely prevalent in 90% of patients, mostly at a moderate level, and a weak positive correlation was observed between anemia severity and VAN trough levels, ICU admission, kidney disease, abnormal liver markers, and inflammatory indices. Microbial isolates were differentially enriched across anemia categories with K. pneumoniae, E. coli, and MRSA peaking in mild anemia and sharply declining in moderate and severe cases. Anemia severity was differentially correlated with P. aeruginosa, creatinine, hypertension, liver disease, albumin, platelets, and derived indices. In adjusted analysis, albumin, age, gender, platelet–neutrophil ratio, kidney disease, ICU admission, and MATH-1SD were independent predictors of anemia. A diagnostic model for anemia based on multiple markers was developed with an accuracy of 77%. Conclusions: Anemia is alarmingly very common in VAN-treated patients with distinct microbial and inflammatory signatures across severity groups, which highlights the need for experimental and longitudinal studies elucidating its pathophysiological mechanisms and clinical implications.