Serum ferritin measurements differ according to the assay used: implications for iron therapy in restless legs syndrome.

Study Objectives: Serum ferritin levels are used to determine the need for iron supplementation in patients with restless legs syndrome. The purpose of this study was to determine whether immunoassay measurement of serum ferritin yields varying levels according to different manufacturers' assays, with resultant variation in cutoff values.

Methods: We compared serum ferritin levels using 116 clinical samples assessed by the Beckman and Roche methods.

Results: Although there was a high correlation between results obtained from the 2 methods (R = 0.99), the absolute values differed. The equivalent ferritin measures determined by the Beckman and Roche methods were 50 μg/dl, 83 μg/dl; 75 μg/dl, 121 μg/dl; 100 μg/dl, 158 μg/dl; and 300 μg/dl, 457 μg/dl.

Conclusions: It is uncertain which assays were used to measure serum ferritin in the seminal studies on which current guidelines for iron therapy for restless legs syndrome are based. In view of this uncertainty, as well as the limited data on which current recommendations are based, clinicians should be flexible in using recommended serum ferritin cutoff values, also using percentage of transferrin saturation. Assuming that Beckman or equivalent assays were used, centers using the Roche method need to adjust the cutoffs for administration of oral iron and intravenous iron recommended by current practice guidelines to avoid withholding treatment for restless legs syndrome patients who might benefit from iron supplementation.

Citation: Silber MH, Block DR, St. Louis EK. Serum ferritin measurements differ according to the assay used: implications for iron therapy in restless legs syndrome. 2025;21(1):65-67.