What is the Wo80 standard and how can kits have different cut-offs although they are standardised against the same international standard?
The Wo/80 Standard is the international standard of the WHO for measuring of anti-dsDNA antibodies. All anti-dsDNA kits which are calibrated against this standard, do use Internation Units (IU/ml) instead of arbitrary units (which is the common quantitative unit in autoantibody testing, because only in very few cases a standard is available).
The Wo/80 is human serum with dsDNA antibodies. The standard has existed since 1985 and is marketed by the Central Laboratory of the Netherlands Red Cross Blood Transfusion Service (CBL) in Amsterdam.
All kits which are calibrated against the Wo/80 Standard have to find it at a level of 100 IU/ml.
Both Varelisa dsDNA Antibody test and EliA dsDNA are calibrated against the Wo/80 standard.
However, both kits have different cut-offs: EliA dsDNA at 15 IU/ml and Varelisa dsDNA Antibodies at 55 IU/ml. This is due to the high heterogeneity of dsDNA antibodies: Some patients make low affinity antibodies that do not bind tightly, do not form very stable complexes or the complex can be separated by minor changes in temperature, ionic strength, pH etc.
Some patients make low affinity antibodies that do not bind tightly AND high affinity antibodies that do bind tightly.
What is the result? Every sample has the potential to behave differently from:
- every other sample
- samples at different times from a patient
- any standard
- any quality control material
- any quality assurance material
This results in a huge variability in results between
Thus, although all tests are standardised against Wo80 and give international units, the result can vary widely between different patient samples. In quality assessment schemes it can be seen that one sample can produce very different results, depending on the method used.
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