Reference values for a heterogeneous ferritin assay and traceability to the 3rd International recombinant Standard for Ferritin (NIBSC code 94/572)

Reference values for Ferritin Flex on the Dimension RxL analyzer calibrated against the 3rd International Standard for Ferritin (recombinant) and N-Latex Ferritin®on the BNA II nephelometer calibrated against the 2nd International Standard for Ferritin (spleen) both from Dade Behring (Marburg, Germany) were established (77 men and 182 women). Exclusion criteria were iron deficiency or iron deficiency anemia, inflammation, liver disease, malignancy, and other hematological or chronic disorders. The reference values (5.0th-95th percentiles) were as follow: for N-Latex Ferritin® - men, 12-399 μg/l; women <50 years, 11-102 μg/l and women ≥50 years, 17-219 μg/l; for Ferritin Flex - men, 14-415 μg/l; women <50 years, 11-111 μg/l and women ≥50 years, 22-224 μg/l. Both assays correlated very closely with each other (r=0.993). The linearity was acceptable down to 2 μg/l for the Ferritin Flex method, but only down to 15 μg/l for the N-Latex Ferritin® assay. The mean recovery of the 3rd International Standard by N-Latex Ferritin®and Ferritin Flex was comparable (∼80%). We conclude that the new Ferritin Flex assay, which is based on the new 3rd International Standard, should be used for ferritin measurement in the routine medical laboratories in the future.