Validation of Nijmegen-Bethesda Assay Modifications to Allow Inhibitor Measurement during Replacement Therapy and Facilitate Inhibitor Surveillance
Published Date:Jun 2012
Source:J Thromb Haemost. 10(6):1055-1061.
Corporate Authors:Hemophilia Inhibitor Research Study Investigators
Blood Coagulation Tests
Enzyme-Linked Immunosorbent Assay
Predictive Value Of Tests
Reproducibility Of Results
Severity Of Illness Index
Pubmed Central ID:PMC4477703
Funding:CC999999/Intramural CDC HHS/United States
As part of a pilot U.S. inhibitor surveillance project initiated at the Centers for Disease Control and Prevention (CDC) in 2006, centralized inhibitor measurement was instituted.
To validate a modified method for inhibitor measurement suitable for surveillance of treated and untreated patients.
710 subjects with hemophilia A were enrolled; 122 had history of inhibitor (HI). Nijmegen-Bethesda assay (NBA) results on 50 split specimens shipped on cold packs and frozen were equivalent (r=0.998). Because 55% of 228 initial specimens had factor VIII (FVIII) activity (VIII:C) present, a heat treatment step was added. Heating specimens to 56°C for 30 minutes and centrifuging removed FVIII, as demonstrated by reduction of VIII:C and FVIII antigen to <1 U/dL in recently treated patients. Among specimens inhibitor-negative before heating, 1 of 159 with negative HI and 5 of 30 with positive HI rose to ≥0.5 Nijmegen Bethesda units (NBU) after heating. Correlation of heated and unheated inhibitor-positive specimens was 0.94 (P=0.0001). The modified method had a CV for a 1 NBU positive control of 10.3% and for the negative control of 9.8%. Based on results on 710 enrollment specimens, a positive CDC inhibitor was defined as ≥ 0.5 NBU. Results were similar when 643 post-enrollment specimens were included. Of 160 enrolled hemophilia B patients, 2 had HI. All others had NBU ≤ 0.2 at enrollment.
The CDC experience demonstrates that this modified NBA can be standardized to be within acceptable limits for clinical tests and can be used for national surveillance.
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