Effect of sampling time and repetition on gingival crevicular fluid and aspartate aminotransferase activity

Tests based on the composition of gingival crevicular fluid (GCF) for detection of active periodontitis require a better understanding of sampling variables than currently exists. We have studied the effects of sample time and repetition on the presence and activity of aspartate aminotransferase (AST). Two 30-second samples of GCF were harvested within 10-minute intervals from 192 teeth with periodontitis. GCF sample size and AST activity were measured. GCF volume and AST activity of first samples were each approximately 10% greater than for second samples. The differences were significant. AST activity correlated positively with gingival index scores and probing pocket depth. Samples were also harvested from groups of 4 teeth during 5-, 10-, 20- and 30-s periods with 1-min intervals and varying sample order. For these samples, first samples contained the greatest amount of enzyme activity, regardless of sample time. When only first samples were considered, the 5- and 10-s samples showed more total activity than the 20- and 30-s samples, and differences were statistically significant. Flow rate for the 5-s sample was always higher than for all other samples, regardless of its position in the sampling sequence. Our observations are consistent with the existence of a reservoir of AST activity that is, in major part, depleted during the first 5 to 10 s of sampling, and that requires a time period of more than 10 min to reequilibrate. Five- to 10-s samples may distinguish active disease better than 20- or 30-s samples, since most of the activity is taken onto the strip in the first few seconds, and the activity is subsequently partly inactivated or diluted by the uptake of fluid less rich in enzyme activity.