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.