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Unclassified Antibody Deficiency (unPAD) Study

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Unclassified Antibody Deficiency in the European Society for Immunodeficiencies (ESID) Registry.

Already > 3,200 level 1 + level 2 forms completed for the unPAD study

We thank everyone for this incredible result so far.

All of you who have not yet started your participation, please reconsider and join this very large cohort of hypogammaglobulinemia patients (unclassified PAD + CVID as controls).

Please note:

The possibility to document the extended Level 2 dataset is offered automatically by the system for all patients with a respective PID-Diagnosis (see table).

Participation in the Study is possible by documenting the respective Level 2 Forms.

If you are unceartain at the moment about the participation you might want to choose the option 'ask me later' .

It is estimated that some 1.5 million people suffer some form of PID within the European Union (EU), of these, only some 60,000 suffer such a severe form that it leads to significant problems very early in life. However, many more patients suffer from less-well described and understood forms of ‘hypogammaglobulinaemia’: deficiency of IgG, IgG-subclass(es), IgM, IgA and/or specific antibody, alone, or in combination(s). These patients often are not recognised and do not visit physicians in specialised/tertiary centres, are mostly not characterised very well immunologically, and are often not treated with the immunodeficiency taken into consideration. Besides, it is not very well known whether and if so how they should be treated, nor whether treatment(s) are useful for some but not all subgroups.

For these patients, several working definitions have been defined separately in the ESID online Registry; they are listed in the table.


ESID Registry Clinical Diagnosis Category

Category in unPAD study

Deficiency of specific IgG (Specific antibody deficiency – SPAD)

unPAD patient

IgA with IgG subclass deficiency

Isolated IgG subclass deficiency

Selective IgM deficiency

Selective IgA deficiency

Unclassified antibody deficiency

Common variable immunodeficiency disorders (CVID)

CVID patient


            The unPAD study is a multi-centre observational cohort study based on ESID online Registry data. The primary objective of the unPAD study is to characterise ‘unPAD patients’ (as defined above), and to compare them with ‘CVID patients’ (see table). To this end, a set of research questions were formulated by the antibody deficiency expert panel of the ESID Registry Working Party, these were built as a level 2 form in the ESID Registry.


For more information, please scan the QR code or go to:


Interested in participation? Send an email to !


Please refer to the section Datasets to view the unPAD dataset.