From Dr. Mirta Arias, Dear George, which is the procedure for determining the cut-off of Bethesda method and Nijmegen? Is there any Excel spreadsheet to perform it? Do you use only normal or normal and patients? Thanks, Mirta
Hello, Dr. Arias, and thank you for your question. For a comprehensive answer, I turned to Amanda Payne, MPH, from the US Centers for Disease Control and Prevention. Ms. Payne provided me with the attached documentation describing the 1975 origin of the Bethesda titer, an article describing the 2012 CDC validation of the Nijmegen Bethesda assay, and the derivation of the formula for computing Nijmegen Bethesda units (NBUs).
The quick answers to your questions are (1) no, I know of no Excel spreadsheet that provides an automated NBU formula, though I suspect a mathematician could develop one quite easily, (2) the NBU positivity cut-off described in the 2012 validation article is 0.5 NBUs, and (3) the assay requires pooled normal plasma diluted in buffered saline providing approximately 100% (100 U/dL or 1.0 U/mL) factor VIII. The method also employs a factor VIII inhibitor positive control and requires that the test specimen and control dilutions be made in factor VIII-depleted plasma or bovine serum albumin (BSA). Inhibitors of 0.5–5.0 NBUs are categorized as low avidity, whereas inhibitors whose titers are greater than 5 NBUs are high avidity. This categorization helps sort out the therapeutic approach to the management of bleeding patients. I hope this is helpful to you and our participants, and I welcome additional questions and updates.
The 1975 description of the Bethesda titer (click or tap): Kasper CK, Aledort LM, Counts RB, et al. A more uniform measurement of factor VIII inhibitors. Thrombos Diathes Haemorrh 1975;34:869–72.
The 2012 description validating the Nijmegen-Bethesda assay (click or tap): Miller CH, Platt SJ, Rice AS, et al. Validation of Nijmegen-Bethesda assay modifications to allow inhibitor measurement during replacement therapy and facilitate inhibitors survellance. J Thromb Haemostas 2012;10:1055–61.
Derivation of the NBU computation formula (click or tap).
Thank you to Amanda Payne for assisting with this information.