What do your hematocrit test results mean?

Hematocrit tests can tell doctors if someone is anemic, which is one of the most common reasons for ordering the test

What is a hematocrit test | Normal hematocrit levels | Low hematocrit levels | High hematocrit levels |

If you’re showing signs of being anemic (which could include fatigue, grumpiness, headaches, or heavy menstrual cycles), your doctor might want to do bloodwork. A hematocrit test is a type of blood test that can detect anemia and other health conditions, which will help your healthcare provider to properly diagnose and treat you. This article describes what hematocrit tests are and helps explain what your hematocrit levels mean.

What is a hematocrit test?

Hematocrit is a measurement of the size and number of red blood cells that someone has. Everyone’s blood is made up of red blood cells, white blood cells, and platelets. The hematocrit (hct) is a measurement of how much of someone’s blood is made up of red blood cells. The test measures by volume but is then expressed as a percentage. If a person has a hematocrit of 40%, this means that he or she has 40 milliliters of red blood cells in 100 milliliters of blood.

Doctors will ask someone to get a hematocrit test as part of a complete blood count (CBC) to see how well they’re responding to a certain treatment and/or to see if they have any underlying health problems. Hematocrit helps measure hemoglobin, which is what’s found in oxygen-carrying red blood cells. It’s important because the body can’t get enough oxygen to function properly without it, says Susan Besser, MD, a family practitioner at Mercy Medical Center in Baltimore, Maryland.

Why are hematocrit levels important?

Hematocrit tests can tell doctors if someone is anemic, which is one of the most common reasons for ordering the test. Symptoms of anemia include tiredness, grumpiness, heavy menstrual periods, cold hands and feet, and poor concentration. Your doctor may ask you to get a hematocrit test done if you have any of those symptoms.

Hematocrit tests, which are sometimes called packed cell volume tests (PCV), can also help tell doctors whether someone has other nutritional deficiencies or health problems such as leukemia, kidney disease, or arthritis. Hematocrit tests are important because they measure how many red blood cells someone has. Too many or too few red blood cells can indicate certain nutritional deficiencies or diseases that doctors will know how to identify.

What to expect during a hematocrit test

During a hematocrit test, you can expect to have a sample of blood taken by a phlebotomist or another healthcare professional who can draw blood. Getting blood drawn can be uncomfortable, but most people only feel a light prick when the needle inserts the vein. If you need to have a hematocrit test done and know that you might get lightheaded, you can always ask to lie down while your blood sample is taken.

How to prepare for a hematocrit test

There are no special preparations needed prior to drawing a blood sample for just a hematocrit test. If your healthcare provider has ordered additional blood tests you may need to avoid eating or drinking for several hours before the test. Your provider will let you know if there are any special instructions you need to follow.

Risks of a hematocrit test

As with most blood tests, there is very little risk to having a hematocrit test. You may experience slight pain, bleeding, or bruising at the spot where the needle was inserted, but most symptoms resolve quickly.

What is a normal hematocrit level?

The average healthy adult should have a normal hematocrit level that ranges between 35% to 50%. A normal hematocrit level for women is 36% to 44%. For men, a normal range is 41% to 50%. The normal numbers vary a little from lab to lab. This means the average adult female’s total blood volume should consist of 36% to 44% red blood cells, and the average adult male’s blood should be 40% to 50% red cells. Depending on their age, normal values for children range between 30% to 44%.

Hematocrit tests are generally pretty accurate. Test results help doctors diagnose their patients with the right health condition so they can give appropriate treatment. It’s possible for certain things to cause a hematocrit test to give inaccurate results though. Here are some factors that commonly cause abnormally high or low hematocrit levels:

• Pregnancy can cause hematocrit levels that are lower than usual
• Any recent blood transfusions
• Living at a high altitude can cause high hematocrit levels
• Dehydration can cause high hematocrit levels

Doctors are aware of what can potentially skew test results, and they have them in the back of their minds when they’re reading results. If your doctor feels that your hematocrit levels may have been affected by something like dehydration, they may ask you to take the test again at a different time.

Symptoms of low hematocrit levels

Having low hematocrit levels, which is sometimes called anemia, often makes people feel under the weather. If you’re having any of the following symptoms, they could mean you have a low red blood cell count:

• Tiredness
• Lack of concentration
• Shortness of breath
• Headaches
• Heavy menstrual cycles
• Grumpiness

If you take a hematocrit test and your test results report low hematocrit levels, this means you have a lower percentage of red blood cells than you should. Many things can cause low hematocrit levels, which can indicate an underlying health condition like:

• Iron-deficiency anemia 
• Vitamin or mineral deficiencies
• Leukemia
• Lymphoma
• Recent blood loss
• Bone marrow problems
• Overhydration

Just because you have low hematocrit levels, doesn’t necessarily mean that you have any of the above conditions. Your doctor will likely run other medical tests and ask you about your medical history to help determine what’s actually happening.

Symptoms of high hematocrit levels

Experiencing certain symptoms may indicate that you need a hematocrit test and that your hematocrit is high. If you’re having any of the following symptoms, you should talk with your doctor about whether or not a hematocrit test is right for you:

• Tiredness
• Shortness of breath
• Flushed skin
• Sweating
• Dizziness
• Joint pain
• Itching
• Headaches

If you’ve taken a hematocrit test and hematocrit is high, this means that you have more red blood cells than what’s considered to be healthy. High hematocrit levels could indicate underlying medical conditions like:

• Dehydration
• Carbon monoxide poisoning
• Congenital heart disease
• Bone marrow disease (polycythemia vera)
• Scarring of the lungs
• Not enough oxygen in the blood (often from lung conditions)
• Erythrocytosis

Having abnormally high levels of red blood cells doesn’t necessarily mean that you have one of the conditions listed above. High hematocrit levels can mean that you might have a serious health condition like heart disease, but your doctor will run other tests to make sure you’re properly diagnosed.

How to lower hematocrit levels / What to do for high hematocrit levels 

If your hematocrit value is high, it is important to work with your doctor to find out why and to treat any underlying conditions. You may be able to reduce your hematocrit level by the following diet and lifestyle changes:

• Avoiding iron supplements 
• Staying hydrated 
• Avoiding alcohol 
• Eating grapefruit 
• Eating bran (it reduces the amount of iron absorbed by the body)
• Moderate exercise
• Stop smoking

Some patients with very high hematocrit levels may require more serious medical intervention or drug therapy. Always follow the treatment plan prescribed by your doctor.

Other than lifestyle changes, your doctor may prescribe a medication to help with high hematocrit levels. Blood clot medications are commonly prescribed because people with too many red blood cells have a higher risk of getting a blood clot. Aspirin (Aspirin coupons | What is Aspirin?) is sometimes recommended by doctors because of its ability to help with blood clots.

Other medications that doctors prescribe for high hematocrit levels are likely to focus on treating the condition that’s causing the body to produce too many red blood cells, like bone marrow or heart disease. Phlebotomy (bloodletting) is a popular way to control high red blood cell counts. In phlebotomy, blood is taken from the veins to make it thinner.

How do you treat abnormal hematocrit levels?

Once you’ve taken a hematocrit test and know whether or not you have high or low hematocrit levels, the next step is figuring out the cause. Treatment will be based on how abnormal the hematocrit is and its underlying cause.

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What to do for low hematocrit levels / How to increase hematocrit levels

People with extremely low red blood cell counts may need to go to the doctor to get intravenous iron or blood transfusions. If there’s an underlying health condition that’s causing the body to produce less red blood cells, then medication might be needed to help stimulate the production of new red blood cells.

Some lifestyle changes can help increase red blood cell counts. Eating a variety of fresh, healthy foods that contain iron, vitamin B-12, and folic acid can prevent anemia. Taking these nutrients in supplement form can also be beneficial.

The best way to learn more about how to treat low or high hematocrit levels is to talk with your doctor or healthcare provider.

Anemia in Pregnancy – Gynecology and Obstetrics

By

Lara A. Friel

, MD, PhD, University of Texas Health Medical School at Houston, McGovern Medical School

Reviewed/Revised Oct 2021 | Modified Sep 2022

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Normally during pregnancy, erythroid hyperplasia of the marrow occurs, and red blood cell (RBC) mass increases. However, a disproportionate increase in plasma volume results in hemodilution (hydremia of pregnancy): hematocrit (Hct) decreases from between 38% and 45% in healthy women who are not pregnant to about 34% during late single pregnancy and to 30% during late multifetal pregnancy. The following hemoglobin (Hb) and Hct levels are classified as anemic:

• 1st trimester: Hb

• 2nd trimester: Hb

• 3rd trimester: Hb

If Hb is

Anemia Red Blood Cell Production Red blood cell (RBC) production (erythropoiesis) takes place in the bone marrow under the control of the hormone erythropoietin (EPO). Juxtaglomerular cells in the kidney produce erythropoietin… read more occurs in up to one third of women during the 3rd trimester. The most common causes are

• Iron deficiency Iron Deficiency Iron (Fe) is a component of hemoglobin, myoglobin, and many enzymes in the body. Heme iron is contained mainly in animal products. It is absorbed much better than nonheme iron (eg, in plants… read more

• Folate deficiency Folate Deficiency Folate deficiency is common. It may result from inadequate intake, malabsorption, or use of various drugs. Deficiency causes megaloblastic anemia (indistinguishable from that due to vitamin… read more

Obstetricians, in consultation with a perinatologist, should evaluate anemia in pregnant Jehovah’s Witness patients (who are likely to refuse blood transfusions) as soon as possible.

Early symptoms of anemia are usually nonexistent or nonspecific (eg, fatigue, weakness, light-headedness, mild dyspnea during exertion). Other symptoms and signs may include pallor and, if anemia is severe, tachycardia or hypotension.

Anemia increases risk of

• Preterm delivery Preterm Labor Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection… read more

• Low birth weight

• Postpartum maternal infections

Diagnosis of anemia begins with CBC; usually, if women have anemia, subsequent testing is based on whether the MCV is low ( 100 fL):

• For microcytic anemias: Evaluation includes testing for iron deficiency (measuring serum ferritin) and hemoglobinopathies Overview of Hemolytic Anemia At the end of their normal life span (about 120 days), red blood cells (RBCs) are removed from the circulation. Hemolysis is defined as premature destruction and hence a shortened RBC life span… read more (using hemoglobin electrophoresis). If these tests are nondiagnostic and there is no response to empiric treatment, consultation with a hematologist is usually warranted.

• For macrocytic anemias: Evaluation includes serum folate and vitamin B12 levels.

• For anemia with mixed causes: Evaluation for both types is required.

Treatment of anemia during pregnancy is directed at reversing the anemia (see below).

Transfusion is usually indicated for any anemia if severe constitutional symptoms (eg, light-headedness, weakness, fatigue) or cardiopulmonary symptoms or signs (eg, dyspnea, tachycardia, tachypnea) are present; the decision is not based on the Hct.

Pearls & Pitfalls

• Hemodilution occurs during pregnancy, but oxygen-carrying capacity remains normal throughout pregnancy.

• The most common causes of anemia during pregnancy are iron deficiency and folate acid deficiency.

• Anemia increases risk of preterm delivery and postpartum maternal infections.

• If Hb is

• Treat the cause of the anemia if possible, but if patients have severe symptoms, transfusion is usually indicated.

About 95% of anemia cases during pregnancy are iron deficiency anemia Iron Deficiency Anemia Iron deficiency is the most common cause of anemia and usually results from blood loss; malabsorption, such as occurs in celiac disease, is a much less common cause. Symptoms are usually nonspecific… read more . The cause is usually

• Inadequate dietary intake (especially in adolescent girls)

• A previous pregnancy

• The normal recurrent loss of iron in menstrual blood (which approximates the amount normally ingested each month and thus prevents iron stores from building up) before the woman became pregnant

Typically, Hct is ≤ 30%, and MCV is

One 325-mg ferrous sulfate tablet taken midmorning is usually effective. Higher or more frequent doses increase GI adverse effects, especially constipation, and one dose blocks absorption of the next dose, thereby reducing percentage intake.

About 20% of pregnant women do not absorb enough supplemental oral iron; a few of them require parenteral therapy. The iron deficit may be calculated, and the iron can often be replaced over one or two infusions. Hct or Hb is measured weekly to determine response. If iron supplements are ineffective, concomitant folate deficiency should be suspected.

Neonates of mothers with iron deficiency anemia usually have a normal Hct but decreased total iron stores and a need for early dietary iron supplements.

Although the practice is controversial, iron supplements (usually ferrous sulfate 325 mg orally once a day) are usually given routinely to pregnant women to prevent depletion of body iron stores and prevent the anemia that may result from abnormal bleeding or a subsequent pregnancy.

Folate deficiency Folate Deficiency Folate deficiency is common. It may result from inadequate intake, malabsorption, or use of various drugs. Deficiency causes megaloblastic anemia (indistinguishable from that due to vitamin… read more increases risk of neural tube defects Overview of Congenital Neurologic Anomalies Congenital brain anomalies cause a spectrum of neurologic deficits; although some may be barely noticeable, others may be fatal. Some of the most serious neurologic anomalies (eg, anencephaly… read more and possibly fetal alcohol syndrome Fetal Alcohol Syndrome Alcohol exposure in utero increases the risk of spontaneous abortion, decreases birth weight, and can cause fetal alcohol syndrome, a constellation of variable physical and cognitive abnormalities. .. read more . Deficiency occurs in 0.5 to 1.5% of pregnant women; megaloblastic macrocytic anemia Megaloblastic Macrocytic Anemias Megaloblastic anemias result most often from deficiencies of vitamin B12 and folate. Ineffective hematopoiesis affects all cell lines but particularly red blood cells. Diagnosis is usually based… read more is present if deficiency is moderate or severe.

Rarely, severe anemia and glossitis occur.

Folate deficiency is suspected if CBC shows anemia with macrocytic indices or high RBC distribution width (RDW). Low serum folate levels confirm the diagnosis.

Treatment is folic acid 1 mg orally twice a day.

Severe megaloblastic anemia may warrant bone marrow examination and further treatment in a hospital.

For prevention, all pregnant women and women who are trying to conceive are given folic acid 0.4 to 0.8 mg orally once a day. Women who have had a fetus with spina bifida should take 4 mg once a day, starting before conception.

During pregnancy, hemoglobinopathies, particularly sickle cell disease Sickle Cell Disease Sickle cell disease (a hemoglobinopathy) causes a chronic hemolytic anemia occurring almost exclusively in people with African ancestry. It is caused by homozygous inheritance of genes for hemoglobin… read more , Hb S-C disease Hemoglobin S-C Disease Hemoglobin S-C disease is a hemoglobinopathy that causes symptoms similar to those of sickle cell disease, but usually less severe. (See also Overview of Hemolytic Anemia.) The heterozygous… read more , and beta- and alpha- thalassemia Thalassemias Thalassemias are a group of inherited microcytic, hemolytic anemias characterized by defective hemoglobin synthesis. Alpha-thalassemia is particularly common among people with African, Mediterranean… read more , can worsen maternal and perinatal outcomes. Genetic screening genetic screening Genetic Screening for Some Ethnic Groups for some of these disorders is available.

Preexisting sickle cell disease, particularly if severe, increases risk of the following:

• Maternal infection (most often, pneumonia Overview of Pneumonia Pneumonia is acute inflammation of the lungs caused by infection. Initial diagnosis is usually based on chest x-ray and clinical findings. Causes, symptoms, treatment, preventive measures, and… read more , urinary tract infections [UTIs] Postpartum Pyelonephritis Pyelonephritis is bacterial infection of the renal parenchyma. Pyelonephritis may occur postpartum if bacteria ascend from the bladder. The infection may begin as asymptomatic bacteriuria during… read more , and endometritis Postpartum Endometritis Postpartum endometritis is uterine infection, typically caused by bacteria ascending from the lower genital or gastrointestinal tract. Symptoms are uterine tenderness, abdominal or pelvic pain… read more )

• Pregnancy-induced hypertension Hypertension in Pregnancy Recommendations regarding classification, diagnosis, and management of hypertensive disorders (including preeclampsia) are available from the American College of Obstetricians and Gynecologists. .. read more

• Heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular (LV) failure causes shortness of breath and fatigue, and right ventricular (RV) failure causes peripheral and abdominal… read more

• Pulmonary infarction Pathophysiology

• Fetal growth restriction Small-for-Gestational-Age (SGA) Infant Infants whose weight is < the 10th percentile for gestational age are classified as small for gestational age. Complications include perinatal asphyxia, meconium aspiration, polycythemia… read more

• Preterm delivery Preterm Labor Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection… read more

• Low birth weight Small-for-Gestational-Age (SGA) Infant Infants whose weight is < the 10th percentile for gestational age are classified as small for gestational age. Complications include perinatal asphyxia, meconium aspiration, polycythemia… read more

Anemia almost always becomes more severe as pregnancy progresses. Sickle cell trait increases the risk of UTIs but is not associated with severe pregnancy-related complications.

Treatment of sickle cell disease during pregnancy is complex. Painful crises should be treated aggressively. Prophylactic exchange transfusions to keep Hb A at ≥ 60% reduce risk of hemolytic crises and pulmonary complications, but they are not routinely recommended because they increase risk of transfusion reactions, hepatitis, HIV transmission, and blood group isoimmunization. Prophylactic transfusion does not appear to decrease perinatal risk. Therapeutic transfusion is indicated for the following:

• Symptomatic anemia

• Heart failure

• Severe bacterial infection

• Severe complications of labor and delivery (eg, bleeding, sepsis)

Hb S-C disease may first cause symptoms during pregnancy. The disease increases risk of pulmonary infarction by occasionally causing bony spicule embolization. Effects on the fetus are uncommon but, if they occur, often include fetal growth restriction.

Sickle cell–beta-thalassemia is similar to Hb S-C disease but is less common and more benign.

Alpha-thalassemia does not cause maternal morbidity, but if the fetus is homozygous, hydrops and fetal death occur during the 2nd or early 3rd trimester.

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