Hello~If your doctor has seen these results and has not said anything about them, then I wouldn't worry, however, if you are concerned, for your own peace of mind, I would contact him/her and say that you are concerned.
A one time low result on these tests is not alarming. If you've recently had an infection, if you've been drinking alcohol, perhaps even if you've been very stressed or anxious, it could affect this test. Some medications can affect it as well.
You should talk to your doctor about it. They may want to monitor it, or if you have any other abnormal tests, take that into consideration.