Validation of calculated globulin (CG) as a screening test for antibody deficiency in an Italian University Hospital

Morbidity and mortality of primary and secondary antibody deficiencies (AD) are frequently associated with diagnostic delays. These could be avoided by a combination of factors including a widespread and effective development in screening tests. Calculated globulin (CG), derived from the difference between serum total protein and albumin levels, reflects immunoglobulin serum levels and has shown to have a predictive value in the early diagnosis of antibody deficiencies. This study investigated the possibility to use low levels of CG to detect antibody deficiency in an Italian University Hospital. First, we conducted an analysis of anonymized adult samples collected at our biochemistry laboratory with a range of calculated globulin levels from 15 to 22 g/l. A CG cut-off of 19 g/l detected subjects with IgG lower than 600 mg/dl with a sensitivity of 70% and a specificity of 75%. To further verify the clinical usefulness of CG, we retrospectively evaluated the relationship between CG values and serum IgG levels in 38 patients diagnosed with CVID at our Institution. Using a CG cut-off of 19 g/l we detected antibody deficiency in 97.3% (37/38) of the subjects present in our cohort. Finally, we chose a CG value of 19 g/l as cut-off for a prospective AD screening program. The results of this study show that a screening CG test can be used as a tool to reduce diagnostic delays, improve long-term prognosis and reduce the healthcare costs of antibody deficiency.