I saw ferning on the slide when I first took the sample, but it was gone several hours later. How long can a sample stay on the slide?

For reliable results, look at samples that have just finished drying. It is possible to see a dry saliva sample several hours after you prepare the slide, but we don’t recommend waiting this long. The sample could be affected by environmental factors like temperature and humidity, which could alter the results you see in the microscope.