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

<b><i>Introduction:</i></b> 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. <b><i>Methods:</i></b> 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. <b><i>Results:</i></b> A total of 550 adult patients were included in the study. The CG value predicting patients with IgG &lt;6 g/L as a screening test was determined as &lt;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 &lt;7 g/L. In the retrospective analysis, 37 of 47 patients (78.7%) with PAD had a CG value of &lt;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 &lt;7 g/L. <b><i>Conclusion:</i></b> The determined CG cut-off value of &lt;20 g/L can be used as a screening test in Turkish adult patients.