The exact biochemical nature of NTBI is unknown, and analytical approaches to measure NTBI vary with respect to testing principle and practical application.
We compared NTBI assays with serum samples from patients undergoing stem cell transplantation for hematologic malignancies (2).
We also compared the bleomycin assay with a chelation assay for the determination of NTBI in the serum of patients with hematologic malignancies.
The patients were enrolled in clinical studies for chelation of NTBI by an investigational apotransferrin product.
We added 30-40 [micro]mol/L FeNTA to obtain serum with fully saturated transferrin and NTBI.
The NTBI assay with iron chelation and colorimetric quantification was carried out according to the method of Gosriwatana et al.
The assay precision was measured using a high and a low serum control, which were prepared by adding FeNTA to normal serum to saturate transferrin and form different concentrations of NTBI (Table 1).
When the transferrin was found only in the iron-saturated form, the NTBI was [greater than or equal to]0.
A clear correlation between hemoglobin and the NTBI concentration could be seen (Fig.
At ferritin concentrations of 5-2470 [micro]g/L (mean [+ or -] SD, 568 [+ or -] 733 [micro]g/L; n = 20), all corresponding NTBI results were <0.
Cyclophosphamide did not interfere with NTBI results: in normal serum, NTBI was not detectable, and in the positive patient sera, the NTBI concentrations remained the same.
NTBI concentrations were measured in 399 patient samples by the bleomycin assay, and the results were compared with transferrin saturation values (Fig.