Reference values for a homogeneous Ferritin assay and traceability to the 3rd International Recombinant Standard for...

Reference values for two ferritin assays (Tina-quanta Ferritin, Enzymun, both Roche Diagnostics, Mannheim, Germany) were established (136 males and 139 females). To rule out inflammation as well as iron deficiency in the reference population, subjects with the C-reactive protein concentration < 5 mg/l, and zinc protoporphyrin < 40 micromol/mol heme and the soluble transferrin receptor < 3 mg/l were selected. Taking into account latent iron deficiency as well as hereditary hemochromatosis the 5-95 percentile range was as follows: male, 27-365 microg/l; female, 13-148 microg/l for Tina-quanta and 12-151 microg/l for Enzymun. The Tina-quanta Ferritin assay showed a very good correlation (r > or = 0.990) to Enzymun ferritin, Ferritin Abbott (Abbott Diagnostics, Delkenheim, Germany), N Latex Ferritin (Dade Behring, Marburg, Germany) and the Ferritin Chiron (Chiron Diagnostics, Fernwald, Germany). However, the slopes of the standard principal component method analysis were calculated to be between 1.03 (Enzymun) and 1.41 (N Latex Ferritin). For four assays the median recovery of the 3rd International Recombinant Ferritin Standard (NIBSC 94/572) measured by serial dilution was 89-109%. The N Latex Ferritin assay recovered half of the target values. Because of the good correlation with other assays, a matrix effect is likely. The question arises whether the manufacturers' agreement on the recombinant ferritin standard would harmonize ferritin measurement.