Sing a lip trill through your entire vocal range, every day – whether you are well or sick. Notice if you have note loss anywhere in your range. This works best if you know your baseline range and what your normal daily fluctuations are. Fluctuations of a semi-tone or so are not a worry, but if over a third of your range is gone, then that is a sign that your vocal folds may be swollen.
Aspirate gradual onset
An aspirate gradual onset is something Jo Estill described in her Estill Voice Training Method. Try to sing a note, but start gradually with an “h” sound first which gently becomes “ah” with a smooth (not abrupt) start. If you find that your voice “clicks” into the sound instead of smoothly easing in, you can infer that you might still be swollen. You are trying to get your vocal folds to come together (adduct) and begin vibrating without an abrupt onset.
High quiet voice
Your upper range and quiet sounds are the measure of your swelling success – i.e. how healed you are after an illness. Once swelling has gone, a singer should be able to sing up to their highest notes with a quiet, small voice. This quiet voice may not sound good, but it may be an indicator that your voice is healed and returning to health. Additional vocal fold swelling tests were explained in the Journal of Voice in 1990 by Anat Keidar, Robert W. Bastian and Katherine Verdolini-Marston in “Simple Tasks For Detecting Vocal Fold Swelling.”