CALIBRATION AND RELIABILITY OF THE PERIOTRON-6000 FOR INDIVIDUAL GINGIVAL CREVICULAR FLUID SAMPLES

The Periotron 6000(R) fluid analyser has become widely used as a diagn ostic tool for a variety of oral diseases and recent work has question ed its reliability. This paper investigates for the first time, the de tailed calibration curves of 2 Periotron 6000 machines across a range of 23 different fluid volumes. Within and between machine reliability is analyzed and the shape of the calibration line determined. The meas urement errors incurred by using a single fluid sample, as opposed to mean values of triplicate samples are also determined. We conclude tha t there are 3 sections to the calibration line, 2 linear and a quadril ateral zone, and that 2 separate regression equations should be used; from 0-0.1 mu l and from 0.1-1.0 mu l. Within machine calibration erro rs were only 3.2 +/- 7.5%, but values for volumes below 0.2 mu l were as high as 18.7%. Using a single fluid sample rather than mean values of multiple samples, incurred a further 4 +/- 4% error, which was as h igh as 7% for volumes lower than 0.12 mu l. Whilst significant differe nces in volume reading existed between different machines (p<0.0004) a nd between the same volumes of different fluids (p<0.00001), individua l Periotron calibrations were extremely reproducible and reliable. We conclude that the Periotron 6000 is a reliable and convenient instrume nt for measuring fluid volumes greater than 0.2 mu l. For volumes lowe r than 0.2 mu l errors in measurement may be too high for some investi gations, but this is likely to be due to problems with evaporation and with measurement technique, rather than errors directly due to the Pe riotron itself. Finally, for optimum accuracy, the digital display sho uld be re-set to zero after each sample is measured.