INTRODUCTION
Antibody deficiency (AD), a subset of immunodeficiencies, is classified
as primary or secondary in etiology1. Secondary
antibody deficiencies (SAD) occur more frequently than primary antibody
deficiencies (PAD)1,2. The most common severe PAD is
common variable immunodeficiency (CVID), which accounts for the majority
of all adult symptomatic primary immunodeficiency (PID) cases on the
European Society for Immunodeficiencies (ESID) registry
(http://www.esid.org)2-4.
SAD is often related to the underlying conditions or treatments
particularly those targeting B cells.
Clinical features of PAD are heterogeneous. Patients may present not
only with recurrent infections but also with manifestations of
autoimmunity, autoinflammation, lymphoproliferation, granulomas, allergy
or malignancy. Furthermore, although PAD may present at any age, it is
often incorrectly felt to be a childhood disease. Therefore, the
accurate diagnosis can be overlooked or delayed5,6.
Diagnostic delays can lead to recurrent infections and irreversible
organ damage2. Also, patients with a wide number of
different diagnoses in a range of different specialist clinics are
receiving immunosuppressive treatments may suffer from
SAD7 and their diagnoses may also be delayed. Focusing
on control of the underlying autoimmune, inflammatory or malignant
disease by clinicians may result in the oversight of developing SAD and
possible serious infectious complications and recurrent severe
infections can lead to delay in treatment as well. Accordingly, a
screening test may be valuable in highlighting a hitherto undiagnosed
antibody deficiency.
Jolles S. et al. defined the calculated globulin (CG) method to avoid
these diagnostic delays. CG is simply obtained by subtracting serum
albumin from serum total protein which is commonly used as part of liver
function tests and routine check-up tests in daily clinical practice.
Since it contains the gamma fraction including immunoglobulins, low CG
is also a reflection of a possible low serum IgG level. In their study,
Jolles S. et al. showed that CG can be used as a screening test for
patients with PAD and SAD2. Subsequently, Pecoraro A.
et al. performed the Italian version of the CG study8.
Following this, Piza C. et al. showed that CG and gamma globulin
obtained from protein electrophoresis can be used as a screening test
for AD in children9.
In this study, we aimed to validate the CG method as a screening test
for AD in Turkish adult patients by comparing its role with gamma
globulin analysis in protein electrophoresis. In addition, we aimed to
investigate possible relationships between CG and clinical features of
the patients.