Comparison of six serum ferritin immunoassays and isoferritin spectrotypes in malignancies

Serum ferritin was measured by six enzyme immunoassays in specimens from patients with digestive cancers (n = 30) and hematologic malignancies (n = 33). Most mean comparisons show significant differences in both groups of patients. In digestive cancers correlations between any two methods are very satisfactory (r > 0.99) but a proportional bias is often observed. In hematologic malignancies, correlations are bad (r < 0.80 in 8 out of 15 correlations) because of many discrepant values. Isoelectric focusing separation of isoferritins was performed in most specimens and the pattern of each serum was compared to the between kit CV. We conclude that an 'acid' spectrotype increases between-kit analytical variability. We try to explain the results taking into account the nature of the immunological systems and the cross-reactions with tissular isoferritins. In conclusion, our results indicate that large differences may be observed in sera from hematologic malignancies (leukemias, lymphomas ... ) We recommend that monitoring be achieved by the same method of measurement.