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.