COVID-19 presents a broad clinical spectrum, ranging from asymptomatic infections to severe, life-threatening illness. Its pathophysiology is primarily driven by systemic inflammation triggered by the cytokine storm. Anemia is known to be highly prevalent among COVID-19 patients and contributes to a worse prognosis. In this context, identifying reliable tools for early risk stratification has become essential.

This study aimed to evaluate the association between hemogram-derived ratios (HDRs) and the onset of anemia, as well as their relationship with markers of severe disease progression, including intensive care unit (ICU) admission and the need for orotracheal intubation (OTI).

We retrospectively analyzed medical records and serial hemograms of 250 adults hospitalized with RT-PCR-confirmed COVID-19 at the Clinical Hospital of UNICAMP, Brazil (April 2020–March 2021). Clinical and laboratory data were reviewed from diagnosis to outcome, with the aim of monitoring disease progression, anemia, and inflammatory markers during hospitalization. HDRs analyzed included neutrophil-to-lymphocyte ratio (NLR), platelet-to- lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), neutrophil-to-platelet ratio (NPR), and systemic immune-inflammation index (SII). Comparisons were made using the Kruskal–Wallis test with post hoc Dunn’s analysis, and Mann–Whitney tests for ICU/OTI subgroups.

Patients were categorized into three groups based on anemia: Group 1 (n = 62; 24.8%) had anemia at admission; Group 2 (n = 115; 46.0%) developed anemia during hospitalization; Group 3 (n = 73; 29.2%) had no anemia. Of the total cohort, 152 (60.8%) required ICU admission and 113 (45.2%) underwent OTI. At diagnosis, the groups that presented anemia (1 and 2) had significantly higher NLR (p = 0.0021), PLR (p = 0.0098), and SII (p = 0.0046) compared with non-anemic patients. On the 7th day of hospitalization, all the HDRs were higher in anemia groups (1 and 2): NLR7D (p < 0.0001), PLR7D (p = 0.0028), MLR7D (p = 0.0092), NPR7D (p = 0.0010) and SII7D (p = 0.0001). On the 14th day, only MLR remained significantly elevated (p = 0.0469). By the end of hospitalization, none of the HDRs differed significantly between groups, except for NPR (p = 0.0163) when comparing group 1 and group 2. At diagnosis, all HDRs except MLR were higher in patients who required intubation or ICU admission (p ≤ 0.0042), and this association suggests their value in early risk stratification. Notably, the NPR was the only index to significantly differ between patients with anemia at admission and those who developed it during hospitalization.

Hemogram-derived ratios (HDRs) may serve as accessible and useful markers for early identification of COVID-19 patients at higher risk of severe outcomes. Elevated HDR values were associated with anemia, ICU admission and intubation, while the neutrophil-to-platelet ratio (NPR) distinguished between different anemia profiles. This reinforces the potential role of HDRs in clinical risk stratification.