Red blood cell count 3.89, all other results normal - cause for concern?

I had some blood work done when I had my physical last week and my RBC result was 3.89. Normal starts at 4.20. None of the other results were out of normal range, though a few were borderline. My doctor wrote “Great lab results! Keep up the good work. Recheck in 1 year.”

He doesn’t seem too concerned by my one low result. Should I be? I don’t really have any symptoms other than anxiety. I eat plenty of red meat, so I really doubt my iron is low.