Methodological considerations in GCF sampling with paper strips: Poor recovery of uncomplexed elastase

The purpose of this study was to assess the recovery of certain proteins from paper strips used for sampling of gingival crevicular fluid (GCF). During a period of 60 min, proteins were eluted in isotonic phosphate-buffered saline, pH 7.4, without detergent. This eluent did not lyse neutrophils applied to the strips, which might otherwise contribute intracellular substances-, e.g., elastase-to the GCF samples. The proteins applied (MW 12-725 kD) were satisfactorily recovered (about 90%). However, free neutrophil elastase, unlike elastase complexed with alpha-2-macroglobulin, could not be recovered from the paper strips. Strips made of polyvinylidene difluoride (Durapore) were also tested and 31% of the applied pure elastase was recovered from them. A comparison of measurements made with a Periotron 6000 on Periopaper and Durapore strips, showed that the values obtained with Durapore were too low for accurate measurements of small volumes of fluid. On the whole, when the elution was made in isotonic buffers at neutral pH and without detergents, the recovery of most proteins was satisfactory and reproducible, and independent of MW in the tested range. However, the study also showed poor recovery of uncomplexed elastase.