A simpler and more sensitive modified catalytic (bleomycin detectable) iron assay

BackgroundIron is ubiquitously distributed in biology, only a miniscule amount exists as free is capable of catalysing production of highly toxic reactive hydroxyl radicle. This free iron also called; labile iron, non-transferrin bound iron or catalytic iron (CI). CI is measured by bleomycin detectable iron assay. The assay as described originally was difficult to perform accurately and reproducibly due to variations of pH in the assay mixture and due to the lack of properly diluted iron standards.MethodsIn our laboratory we modified the assay for serum/plasma so that the variations of pH in assay medium were constantly between 7.4 and 7.6 using acid diluted iron standards by multiple treatments of Chelex resin which is alkaline.ResultsIntra assay CV for low, medium, and high levels of catalytic iron was 0.05%, 0.61% and 0.68% whereas the interassay CV was 0.06%, 0.96% and 0.28% respectively. The modified assay is highly sensitive being able to detect levels as low as 0.1 μmoles/l. In patients on maintenance haemodialysis CI measured by the original assay failed to detect any catalytic iron in almost all of these samples whereas by modified method it was measurable in all patients with a mean of 0.66 ± 0.10 μmoles/l. Normal values for catalytic iron in subjects having no comorbidities measured by modified method is 0.11 ± 0.06 μmoles/l.ConclusionsThe modified assay is reproducible and more sensitive than original assay and has been validated in several clinical studies.