Impact of Elecsys Folate III assay modifications on serum folate results and folate deficiency classification
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Published on: June 28, 2024
Martina De Matteis1, Davide Ferrari2, Eleonora Sabetta1
1Laboratory Medicine Service, IRCCS Ospedale San Raffaele, 20132 Milan, Italy.
Background:
The clinical value of serum folate testing has been increasingly questioned, largely based on evidence from countries with mandatory folic acid fortification where deficiency is uncommon. Whether these conclusions apply to non-fortified European populations remains uncertain. Moreover, successive modifications of the Roche Elecsys® Folate III assay may have influenced measured folate concentrations and the estimated prevalence of deficiency.
Methods:
We retrospectively analyzed 178,323 serum folate measurements from patients tested at the San Raffaele Hospital (Milan, Italy) between January 2022 and June 2026. Monthly mean folate concentrations and the proportion of tests below the laboratory-defined decision limit (5.38 ng/mL) were evaluated in relation to successive reagent updates, including the introduction of a biotin-tolerant assay version and the subsequent manufacturer corrective action.
Results:
Mean serum folate concentrations remained stable throughout 2022, increased during 2023, declined markedly after implementation of the updated assay, and rose again following the introduction of corrected reagent lots in 2025. The proportion of tests below the laboratory-defined decision limit increased significantly from 31.2 ± 3.3% during 2022-2023 to 42.9 ± 3.8% during 2024-2026 (P < 0.001). Although mean folate concentrations increased following implementation of the 2025 corrective action, it had little apparent effect on the proportion of results below the laboratory-defined decision limit.
Conclusions:
Modifications of the Elecsys Folate III assay were temporally associated with substantial changes in serum folate measurements and an increase of more than 10 percentage points in the proportion of results below the laboratory-defined decision limit. These findings indicate that assay-related bias, particularly at low folate concentrations, may affect the estimates of the proportion of results below the laboratory-defined decision limit, and conclusions regarding the clinical utility and cost-effectiveness of serum folate testing. Analytical standardization should therefore be considered when interpreting serum folate data.
