What might affect the results of a red blood cell count?

Many things. A low rbc count is anemia, and causes include nutritional deficiencies (iron, b12, folic acid), bleeding, chronic illnesses of various kinds, malignancies, and primary bone marrow diseases to name a few. High rbc counts (polycythemia), can occur if there is a lack of oxygen in the blood (lung disease, sleep apnea, smoking for example) or with a blood disorder that causes too many rbcs to be made.