Validation of a rapid fluorescence immunoassay for soluble interleukin-2 receptor α in a pediatric population

The objective of this study was to assess the analytical performance of an automated fluorescence immunoassay (FIA) on the ProteinSimple Ella for rapid measurement of sIL-2 Rα in pediatrics.

Analytical performance evaluation included imprecision, linearity, accuracy, and reference interval establishment. Accuracy was evaluated via method comparison with a chemiluminescent immunoassay (CMIA) through split sampling of EDTA plasma (n = 28). Reference intervals were established per CLSI guidelines (EP28-A3) using plasma from 222 metabolically stable outpatients aged 0 to 19 years.

Imprecision at quality control concentrations of 34 and 1943 pg/mL was 5.0% and 6.9%, respectively. The method was linear across the analytical measuring range. A strong linear correlation between FIA and CMIA (slope: 0.99, bias: -10%, R = 0.99) was found. It was determined that the 2400 U/mL clinical cutoff is equivalent to 10,320 pg/mL. sIL-2 r concentrations were inversely correlated with age. Age-specific reference ranges were established: (1) 0 to <6 years: 1377 - 5022, (2) 6 to <14 years: 851 - 3288, and (3) 565-2499 pg/mL.

Characterization of the analytical performance of the automated FIA for sIL-2 Rα measurement and establishment of age-specific reference ranges is expected to facilitate future investigations of this biomarker in children and adolescents.