Existe-t-il un intérêt à étudier par électrophorèse les protéinuries « quantitativement normales » ?

In this retrospective study over 6 years (658 patients, M/F: N = 353/N = 305, age: 60 ± 16 years), the usefulness of investigating « quantitatively normal » (< 0.15 g/24 hours) proteinuria by electrophoresis using the Hydragel protéinurie® kit (Sebia) was evaluated. Total proteinuria was 0.08 g/L (median: 0.05-0.89 g/L). In 83.7% of cases, urinary electrophoresis (EP) was normal; pathologic profiles were free light chain overload (N = 93), intact immunoglobulin overload (N = 8), mixed profiles (glomerular and tubular) and one case of Plasmion® interference. All patients (except two from hematology) with an overload profile had an abnormality in the β- or γ-globulins by serum EP, most frequently a monoclonal peak (median: 24.1 g/L, < 0.5-75.2 g/L). Free light chains quantification by densitometry was possible in 26% of cases and when proteinuria was above 0.08 g/L. Mixed profiles corresponded to incomplete or inaccurate 24 hours urinary volume. EP analysis of quantitatively normal proteinuria (< 0.15 g/24 hours) thus appears useless in the absence of an associated abnormality of the β- or γ-globulin by serum EP (monoclonal peak, hypogammaglobulinemia). In the presence of a monoclonal peak in the serum or an hypo-γ-globulinemia, the Hydragel protéinurie® kit allows the detection (and in some cases the quantification) of free light chains when their concentration is above ~15 mg/L.