Hematocrit
Also known as: Hct, PCV
What Does Hematocrit Measure?
Hematocrit (Hct), also known as packed cell volume (PCV), measures the percentage of your total blood volume that is made up of red blood cells. When a blood sample is spun in a centrifuge, the red blood cells settle to the bottom, and the hematocrit value represents the proportion of that packed red cell layer relative to the total blood volume. It is expressed as a percentage, so a hematocrit of 45% means that 45% of your blood consists of red blood cells.
Why Does Hematocrit Matter?
Hematocrit is a critical indicator of your blood's oxygen-carrying capacity. Red blood cells contain hemoglobin, the protein that transports oxygen from your lungs to every tissue and organ in your body. An abnormally low hematocrit signals anemia, which can cause fatigue, weakness, and organ stress due to insufficient oxygen delivery. Conversely, an abnormally high hematocrit thickens the blood, raising the risk of dangerous blood clots, stroke, and cardiovascular complications. Hematocrit is routinely included in a complete blood count (CBC) and is one of the most commonly ordered lab tests in clinical medicine.
Normal Ranges
Males
41–53%
Females
36–46%
Children
Varies by age; newborns: 44–64%, infants (6 months): 30–40%, children (1–6 years): 32–40%, children (7–18 years): 33–45%
Causes of High Levels
- Polycythemia vera – a bone marrow disorder causing overproduction of red blood cells
- Chronic hypoxia – long-term low oxygen conditions such as COPD, sleep apnea, or high-altitude living stimulate increased red blood cell production
- Dehydration – reduced plasma volume concentrates red blood cells, artificially elevating the percentage
- Performance-enhancing drug use – erythropoietin (EPO) or anabolic steroid use increases red blood cell production
- Smoking – carbon monoxide from tobacco reduces oxygen delivery, triggering compensatory red blood cell production
- Congenital heart disease – certain cardiac conditions that reduce blood oxygenation lead to elevated hematocrit as a compensatory response
Causes of Low Levels
- Iron deficiency anemia – insufficient iron impairs hemoglobin synthesis and reduces red blood cell production
- Vitamin B12 or folate deficiency – essential for red blood cell maturation; deficiency leads to fewer, larger, less functional cells
How to Improve Your Hematocrit
Diet
- Increase iron-rich foods such as red meat, chicken liver, oysters, lentils, and spinach to support red blood cell production
- Consume vitamin C-rich foods (citrus, bell peppers, strawberries) alongside iron-containing meals to enhance iron absorption by up to 3-fold
- Eat folate-rich foods such as dark leafy greens, beans, avocado, and fortified cereals to support healthy red blood cell maturation
- Include vitamin B12 sources such as eggs, dairy, meat, and fish, or fortified plant-based foods for vegans and vegetarians
- Avoid consuming tea, coffee, or calcium-rich foods at the same time as iron-rich meals, as these inhibit iron absorption
Supplements
- Iron supplementation (ferrous sulfate 325 mg once daily or as directed) for confirmed iron deficiency anemia – always confirm deficiency with lab tests before supplementing
- Vitamin B12 (1,000 mcg/day orally or as prescribed via injection for absorption disorders) to correct deficiency-related anemia
- Folate/folic acid (400–800 mcg/day) to support red blood cell production, especially important during pregnancy
- Vitamin C (250–500 mg taken with iron supplements) to enhance non-heme iron absorption
Related Biomarkers
Frequently Asked Questions
What is the difference between hematocrit and hemoglobin?
Hematocrit measures the percentage of blood volume occupied by red blood cells, while hemoglobin measures the actual concentration of the oxygen-carrying protein inside those red blood cells, expressed in grams per deciliter (g/dL). The two values are closely related — as a rough rule of thumb, hemoglobin is approximately one-third of the hematocrit value. Both are included in a standard CBC and together give a fuller picture of your red blood cell health and anemia status.
Can dehydration cause a falsely high hematocrit?
Yes, dehydration is one of the most common causes of a transiently elevated hematocrit. When you are dehydrated, your plasma (the liquid portion of blood) decreases, but the number of red blood cells stays the same. This makes red blood cells appear to occupy a higher percentage of the total blood volume. Rehydrating adequately before a blood draw and drinking plenty of fluids in general can prevent this misleading result. If a high hematocrit is detected, your doctor may retest after rehydration to determine whether a true elevation exists.
What are the symptoms of a low hematocrit?
A low hematocrit reflects anemia, and symptoms can range from mild to severe depending on how low the value is and how quickly it declined. Common symptoms include persistent fatigue and weakness, shortness of breath especially with physical activity, dizziness or lightheadedness, pale skin or pale inner eyelids, rapid or irregular heartbeat, difficulty concentrating, and cold hands and feet. Severe anemia can cause chest pain, fainting, and organ stress. Many people with mild anemia have no noticeable symptoms, which is why routine blood testing is important.