Impact of Optimizing the Lower Limit of Normal for Ferritin on Iron Deficiency Diagnosis and Treatment Patterns: A Pre and Post‐Intervention Study Using <scp>EHR</scp> Data

Iron deficiency, with or without anemia (IDA or IDWA, respectively), is one of the most prevalent and underdiagnosed conditions globally, particularly in women. In September 2023, Rochester Regional Health (RRH) increased the lower limit of normal (LLN) for ferritin from 10 ng/mL in women and 22 ng/mL in men to a unified threshold of 30 ng/mL, aligning with emerging consensus guidelines. This study evaluates the impact of this clinical laboratory intervention on IDWA/IDA diagnosis and treatment patterns. We conducted a retrospective cohort study using Epic's SlicerDicer tool, comparing patients with ferritin levels < 30 ng/mL during two 1.5-year periods before and after ferritin LLN update. Primary outcome was the rate of IDWA or IDA diagnoses. Secondary outcomes included individual diagnosis rates, rates of IDWA or IDA diagnosis in males and females, iron prescriptions, hematology referrals, number of patients undergoing endoscopy procedures, and number of packed red blood cells (pRBCs) transfusions. Relative risks (RR) with multiplicity corrected confidence intervals (CI) were calculated for the primary and secondary outcomes. Subgroup analyses were stratified by sex, age, race, ferritin levels, and ordering department. Changes in mean ferritin and hematocrit levels at 3-6 months post-test were also compared using Welch's t-test. Among patients with ferritin levels < 30 ng/mL, 22 478 were identified in the pre-intervention period and 27 699 in the post-intervention period. The rate of IDWA or IDA diagnosis increased from 51.0% to 58.5% (RR 1.15; CI: 1.12-1.17; p < 0.001). This increase was more pronounced among females (49.4% to 58.0%; RR 1.17; CI: 1.14-1.21) compared to males (57.0% to 60.2%; RR 1.06; CI: 1.01-1.11). Diagnoses of IDWA rose by 47% (RR 1.47; CI: 1.38-1.57), while IDA increased by 7% (RR 1.07; CI: 1.04-1.10). Prescriptions for oral and IV iron increased by 15% and 17%, respectively, while endoscopy procedures increased by 23%. Among department specialties, surgical departments had the highest relative increase in IDWA/IDA diagnosis rates (RR 1.34; 95% CI: 1.21-1.49). Ferritin levels increased more substantially after the intervention at the 3-6-month follow-up (mean difference: 6.9 ng/mL; 95% CI: 5.7-8.1), with a more pronounced rise among females (mean difference: 8.2 ng/mL; 95% CI: 6.9-9.5) compared to males (mean difference: 4.0 ng/mL; 95% CI: 1.4-6.6). Hematocrit levels showed a modest increase in both periods, though the differences were not clinically significant. Transitioning to an evidence-based higher, sex-independent ferritin LLN significantly improved the identification and treatment of iron deficiency, particularly among women and non-anemic patients. These findings support broader adoption of revised ferritin thresholds to enhance early detection and intervention for iron deficiency in clinical practice.