A hematocrit test measures the proportion or percentage of red blood cells in your blood. It reflects how much of your blood volume is made up of red blood cells, which are responsible for carrying oxygen throughout the body
. Specifically, hematocrit is expressed as a percentage of the total blood volume. For example, a hematocrit of 42 means that 42% of the blood's volume consists of red blood cells, with the remainder being plasma, white blood cells, and platelets
. This test is commonly part of a complete blood count (CBC) and helps diagnose or monitor conditions such as anemia (low red blood cells), polycythemia (high red blood cells), dehydration, and other disorders affecting blood
. Normal hematocrit ranges vary by sex and age, typically about 40.7–50.3% for males and 36.1–44.3% for females. Abnormal levels can indicate various medical conditions, including blood loss, nutritional deficiencies, lung or heart disease, or living at high altitude
. In summary, hematocrit measures the volume percentage of red blood cells in blood, providing important information about oxygen-carrying capacity and overall blood health
