Red Blood Cell Count (RBC count) measures the number of red blood cells in a specific volume of blood. These cells are crucial for transporting oxygen from the lungs to the rest of the body and returning carbon dioxide for exhalation. A normal RBC count varies by age and sex, typically ranging from 4.2 to 6.1 million cells per microliter for men and 3.6 to 5.4 million for women. A low RBC count may indicate conditions like anemia, while a high count could suggest dehydration or other health issues. Doctors often use this test as part of a complete blood count to assess overall health and diagnose potential problems.