What could it mean if your blood test reveals a low c 3 level?

How low?: Labs mean nothing in isolation. If this is a search for a possible lupus flare, or a workup for rheumatologic disease, and the C3 level is quite low, it may actually be important. Reference ranges are set so that a few percent of healthies fall outside on either side. If the lab work was a screen and you're not far outside, don't worry.

Be skeptical: And ask if there are any other related abnormal tests or physical findings. If you are well, a low C3 alone is not a cause for concern.