A hematocrit test is a routine blood examination that measures the proportion of red blood cells in your total blood volume. This common test helps medical professionals assess overall health and can indicate various underlying conditions. It is frequently included as part of a complete blood count (CBC), providing a quick snapshot of your body’s red blood cell status.
What Hematocrit Measures
Hematocrit (Hct) quantifies the percentage of red blood cells in your blood. For instance, a hematocrit reading of 45% means that 45% of your blood volume consists of red blood cells, with the remaining portion comprising white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen from your lungs to tissues and organs, making hematocrit a direct indicator of your blood’s oxygen-carrying capacity. The measurement is typically performed using an automated machine as part of a complete blood count (CBC).
Interpreting Your Hematocrit Levels
Normal ranges for hematocrit can vary depending on factors such as age, sex, and the specific laboratory conducting the test. For adult males, a typical range falls between 41% and 50%, while for adult females, it is usually between 36% and 44%. For infants and newborns, these ranges differ, with newborns typically having higher levels, around 45% to 61%, and infants ranging from 32% to 42%.
A hematocrit value above the normal range indicates a higher proportion of red blood cells, a condition sometimes referred to as erythrocytosis. Conversely, a reading below the typical range suggests a lower proportion of red blood cells, which is commonly known as anemia. It is important to compare your results to the specific reference range provided by the laboratory performing your test, as these ranges can have slight variations.
Factors Influencing Hematocrit Results
Several factors and medical conditions can cause hematocrit levels to be either high or low. Elevated hematocrit can result from dehydration, which concentrates the blood. Chronic low oxygen conditions, such as chronic obstructive pulmonary disease (COPD), sleep apnea, or living at high altitudes, can stimulate the body to produce more red blood cells, increasing hematocrit. Polycythemia vera, a bone marrow disorder, also causes high hematocrit due to excessive red blood cell production. Smoking can also elevate hematocrit from increased carbon monoxide exposure.
Conversely, low hematocrit levels are often associated with various types of anemia, indicating an insufficient number of healthy red blood cells. Iron-deficiency anemia, a common type, occurs when the body lacks enough iron to produce hemoglobin, the oxygen-carrying protein in red blood cells. Blood loss from injury, surgery, heavy menstrual periods, or internal bleeding (e.g., ulcers, colon cancer) can also reduce hematocrit. Kidney disease can contribute to low hematocrit if kidneys do not produce enough erythropoietin, a hormone signaling bone marrow to make red blood cells. Bone marrow issues, such as those from leukemia, other cancers, or chemotherapy drugs, can also impair red blood cell production, resulting in low hematocrit.