Tests with the QED were easy to perform, although difficulties
were sometimes encountered in filling the capillary tube
with saliva. This might reflect variations in the composition of
mixed whole saliva (e.g., its viscosity and amount of particulate
matter). However, when this happened, the quality assurance
spot did not change color, so the test was aborted and a new
QED test was made. If bubbles of air entered the capillary tube
during the sampling procedure, the endpoint was more difficult
to read; however, this occurrence dfd not negate the results,
provided that the QA Spot changed color.