Thymic stromal lymphopoietin (TSLP) seems a promising asthma biomarker. In earlier studies, mainly the serum concentration of TSLP was investigated. The aim of the present study was to compare the TSLP concentration measured by two different ELISA kits in the serum, induced sputum, and exhaled breath condensate in asthma, COPD, and control subjects. The study included 24 asthmatics, 36 patients with COPD, and 12 controls. TSLP concentration was measured with the use of R&D and EIAab commercial ELISA kits. The results obtained with the EIAab kit were 3 to even 45-fold higher than those measured with the R&D kit. Significant differences between the investigated groups were found only for the TSLP concentration in induced sputum. When the R&D kit was used, the highest TSLP levels in induced sputum were found in asthmatics, while the EIAab kit showed the highest TSLP levels in controls. The distribution of results in the Bland-Altman plot was typical for a proportional constant error. TSP concentration in induced sputum might be a more reliable asthma biomarker than serum TSLP. We conclude that TSLP level is highly dependent on the ELISA kit used for the measurement. Thus, judgement on TSLP results obtained with different assays might be confusing and lead to wrong conclusions.
Keywords: Airway obstruction; Exhaled breath condensate; Induced sputum; Serum; TSLP.