Correlation of serum protein electrophoresis with nephelometry in the diagnosis of hypogammaglobulinaemia

Aim Serum protein electrophoresis (SPE) provides an opportunity for the identification of hypogammaglobulinemia. This study was performed to assess the correlation between the lower limit of the gamma globulin reference range following introduction of a new method of SPE and immunoglobulin G (IgG) levels measured by nephelometry. Methods Reference ranges were determined for SPE (SEBIA Hydrasys 2) by analysis of 120 normal samples. Samples without paraproteins ( n  = 122) were subsequently analysed by both SPE and nephelometry. Samples with gamma globulin values ≤7 g/L were preferentially chosen to concentrate on the more clinically relevant lower limit cut-off. Results The gamma globulin levels estimated by SPE and IgG levels by nephelometry correlated strongly (R 2  = 0.901). However, the reference range determined by the guidelines had a low sensitivity (53%) and good specificity (96%) for identifying hypogammaglobulinemia. With the adjusted lower limit of 6.4 g/L, the sensitivity improved to 93% while good specificity was maintained at 92%. Discussion SPE correlates strongly with nephelometry. This study highlights that even with stringent determination of the reference range as per recommended guidelines, ongoing evaluation is necessary to refine the limits in order to maximise the detection of clinically significant abnormalities.