67: Susceptibility of Commonly Used Ferritin Assays to the Classic Hook Effect

The mechanism of false negative immunoassay results due to the hook/prozone effect is well known. However, it remains unclear which assays are most susceptible and at what concentrations the effect becomes significant. The analytes most vulnerable to hook-mediated false negative results are those with physiologic and pathologic concentrations spanning several orders of magnitude. Ferritin, an iron storage protein and an indicator of iron status, is an acute phase reactant with serum concentrations that can exceed 10,000 ng/mL (normal range 10-230 ng/mL). We had a series of specimens from a patient undergoing chimeric antigen receptor modified (CAR) T-cell therapy, which we expected would show a hook effect in ferritin assays. Given the lack of harmonization between immunoassay platforms, we sought to evaluate how ferritin quantification was affected by these very high ferritin concentrations in commonly used analyzers. Ferritin samples with concentrations ranging from approximately 150,000 ng/mL to approximately 999,100 ng/mL (n = 7) were measured on six platforms: Beckman DxI, Siemens Vista, Siemens Immulite XPi, Vitros 3600, Siemens Centaur and Roche Cobas e600. Each specimen was run neat and on dilution. If the concentration exceeded the AMR, additional dilutions were performed. The DxI showed falsely decreased ferritin results in all samples. The Centaur and Immulite showed falsely decreased results when concentrations were greater than 150,000 ng/mL while the Cobas and Vista had a much higher threshold, of greater than 500,000 ng/mL. The Vitros showed no evidence of hook effect. For each sample producing falsely decreased results, the following range of neat results were observed: 160-1,500 ng/mL (actual ≈999,000 ng/mL); 160-1,600 ng/mL (actual ≈930,000 ng/mL); 220-1,850 ng/mL (actual ≈750,000 ng/mL); 300-660 ng/mL (actual ≈450,000 ng/mL); 380-850 ng/mL (actual ≈330,000 ng/mL); 480-1,000 ng/mL (actual ≈240,000 ng/mL); 1,000 ng/mL (actual ≈160,000 ng/mL). In conclusion, ferritin concentrations greater than 400,000 ng/mL are rare but may become more common as CAR T-cell therapy gains broader use for treatment of hematologic malignancies. Most commercially available immunoassays are ill-equipped to accurately quantify the high concentrations of ferritin in these patients and will likely lead to the reporting of erroneous results.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.