Expect a few hertz of difference between runs, and sometimes more. Your speaking pitch rises when you are loud, excited, nervous or reading in a performance voice, and drops when you are tired or relaxed. Many people speak a little lower in the morning, and a cold, allergies or a long day of talking can lower or roughen your voice for a while.
To compare results fairly, keep everything else the same: the same passage, the same microphone and distance, a quiet room and a similar time of day. Then look at the trend across several tests rather than any single number. For a plain chart of typical values by age and sex, see average voice frequency; if you mostly care how low you sound, the deep voice test turns the same measurement into a depth score.
Singing is a different job. A voice frequency test for speech looks for your everyday pitch, while singing covers a much wider span with long, held notes. To see the note you are singing in real time, use the voice tuner.