Anemia and Red-Cell Size Across Estimated Glomerular Filtration Rate in a Hospital Laboratory Cohort

Background/Objective: Anemia patterns may differ between population and hospital-tested cohorts. This paper aims to examine anemia frequency and red-cell size across estimated glomerular filtration rate (eGFR) in hospital records. Methods: This retrospective cross-sectional study included 37,831 adults aged 18–100 years tested at King Khalid Hospital, Saudi Arabia, during 2017–2021. For each individual, one complete blood count (CBC) record and one creatinine record from the same calendar month were analyzed. eGFR was calculated using the 2021 CKD-EPI creatinine equation. Modified Poisson, logistic and natural cubic spline models adjusted for age, sex, and calendar year. Results: Anemia occurred in 8762 participants (23.2%): 22.9%, 17.1%, 34.6%, and 72.1% at eGFR ≥90, 60–89, 30–59, and <30 mL/min/1.73 m2, respectively. Relative to eGFR 60–89, adjusted prevalence ratios (PRs; 95% confidence intervals [CIs]) were 1.26 (1.19–1.33) for ≥90, 1.90 (1.75–2.07) for 30–59, and 3.98 (3.69–4.30) for <30. The association was nonlinear (p < 0.001). Among participants with anemia, the normocytic proportion increased from 56.6% at eGFR ≥90 to 82.7% at <30. In men, the adjusted normocytic-versus-microcytic odds ratio (OR) for <30 versus 60–89 was 2.70 (1.71–4.27). Conclusions: eGFR < 60 was associated with more frequent anemia. The proportion of anemia classified as normocytic was also greater in lower eGFR categories. Based on same-month CBC and creatinine records, these associations do not confirm CKD or determine anemia etiology.