Validation of assays for inflammatory mediators in sputum

Commercially available immune assays are being used with increasing frequen cy in the study of lung inflammation. However, their performance in complex biological fluids is rarely assessed, The authors wished to assess their r eliability to determine whether the results obtained in sputum samples can be easily interpreted. The reproducibility of several such assays was therefore determined togethe r with their ability to recover known amounts of pure reagent. Sputum sol p hase was obtained from several patients with chronic lung disease and used together with the reagents in a series of "spiking" and dilutional experime nts. Results confirmed that the enzyme assay for myeloperoridase and the immune assays for interleukin-8, leukotriene B-4 and secretory leukoproteinase inh ibitor were all reproducible (intra-assay coefficient of variation 3.8-7.7% ). Furthermore, each of these assays gave >85% recovery of a "spike" with p ure reagent. However, the immune assay for myeloperoxidase (although reprod ucible) gave poor recovery and was dependent on the degree of sample diluti on and elastase content. These studies confirm that the reliabilities of fluid phase measurements sh ould be assessed before being widely applied to complex biological samples.