Calculated Globulin Is Clinically Useful as a Screening Test for Antibody Deficiency in Turkish Adult Patients

Heterogeneous clinical features of antibody deficiency (AD) may cause diagnostic delays. Calculated globulin (CG) (total protein minus albumin) has been proposed as a screening test to prevent morbidity due to diagnostic delays in AD. Our aim was to validate CG as a screening test for AD in Turkish adult patients by comparing its role with gamma globulin analysis in protein electrophoresis.

Fifty serum samples were randomly collected for each level of CG from 15 to 25 g/L and tested for serum IgG, IgA, IgM levels and protein electrophoresis. Cut-off values predicting low IgG levels were calculated for electrophoretically determined gamma globulin and CG. Additionally, the data of 47 patients followed up in our clinic with a diagnosis of primary antibody deficiency (PAD) were retrospectively analyzed.

A total of 550 adult patients were included in the study. The CG value predicting patients with IgG <6 g/L as a screening test was determined as <20 g/L with 83.8% sensitivity and 74.9% specificity. The gamma globulin value which predicted patients with the same IgG value of 89.0% sensitivity and 89.4% specificity was determined as <7 g/L. In the retrospective analysis, 37 of 47 patients (78.7%) with PAD had a CG value of <20 g/L at the time of the diagnosis and all 13 patients (100%) whose gamma globulin values were measured at the time of the diagnosis had a gamma globulin value of <7 g/L.

The determined CG cut-off value of <20 g/L can be used as a screening test in Turkish adult patients.