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Hematocrit determination

What is this test?

This test measures the volume (amount) of red blood cells (RBC) compared to other components in blood. Test results are reported as a percentage or as a decimal fraction of whole blood. This test may be used to evaluate or manage diseases such as end-stage renal (kidney) disease, or heart failure[1][2][3][4][5].

What are other names for this test?

  • Haematocrit
  • Haematocrit determination
  • Haematocrit - PCV
  • Hct - Haematocrit
  • Hct - Hematocrit
  • Hematocrit
  • Hematocrit - PCV

What are related tests?

Why do I need this test?

Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. You may need this test if you have:

  • Acute excessive bleeding
  • Acute gastrointestinal hemorrhage
  • Acute post-streptococcal glomerulonephritis
  • Burn caused by heat
  • Ehrlichiosis
  • End-stage kidney disease
  • Hantavirus pulmonary syndrome
  • Heart failure
  • Increased red blood cells
  • Iron deficiency anemia
  • Meckel's diverticulum
  • Pancreatitis
  • Pre-eclampsia
  • Shock from blood loss
  • Shock from heart not pumping blood

When and how often should I have this test?

When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.

Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.

The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.

How should I get ready for the test?

Venous or capillary blood:

Before having blood collected, tell the person drawing your blood if you are allergic to latex. Tell the healthcare worker if you have a medical condition or are using a medication or supplement that causes excessive bleeding. Also tell the healthcare worker if you have felt nauseated, lightheaded, or have fainted while having blood drawn in the past.

Avoid strenuous exercise before this test[6].

Umbilical cord blood:[6]

Ask the healthcare worker for information about how to prepare for this test.

How is the test done?

A sample of venous, capillary, or umbilical cord blood may be collected for this test.

Venous blood:

When a blood sample from a vein is needed, a vein in your arm is usually selected. A tourniquet (large rubber strap) may be secured above the vein. The skin over the vein will be cleaned, and a needle will be inserted. You will be asked to hold very still while your blood is collected. Blood will be collected into one or more tubes, and the tourniquet will be removed. When enough blood has been collected, the healthcare worker will take the needle out.

Capillary blood:

Common sites to collect a capillary blood sample are the fingertip and earlobe. Infants often have a capillary blood sample taken from the heel of the foot. Once the site is selected, the healthcare worker may heat the area with a warm compress to ensure adequate blood flow. The area will be cleaned with antiseptic. A small needle is used to make a cut in the skin surface, and the area may be squeezed gently to produce blood. The blood is collected in small collection device.

Umbilical cord blood:[6]

A method called percutaneous umbilical cord blood sampling may be used to collect an umbilical cord blood sample. For this method, a needle is inserted through the pregnant mother's abdomen and into the umbilical cord. Ultrasound is used to help guide the needle. Samples of the unborn baby’s umbilical cord blood are drawn out for testing. When enough blood is collected, the needle is removed.

How will the test feel?

The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the test. Inform the person doing the test if you feel that you cannot continue with the test.

Venous or capillary blood:

During a blood draw, you may feel mild discomfort at the location where the blood sample is being collected.

Umbilical cord blood:

There are several different ways that a cord blood sample may be collected. Depending on the procedure used to obtain the sample, the test may be uncomfortable. Ask the healthcare worker to explain how the test may feel.

What should I do after the test?

Venous blood:

After a blood sample is collected from your vein, a bandage, cotton ball, or gauze may be placed on the area where the needle was inserted. You may be asked to apply pressure to the area. Avoid strenuous exercise immediately after your blood draw. Contact your healthcare worker if you feel pain or see redness, swelling, or discharge from the puncture site.

Capillary blood:

After capillary blood collection is complete, cotton will be placed over the site and held firmly until the bleeding has stopped. A bandage or cotton may be secured over the site.

Umbilical cord blood:

Depending on the procedure used to obtain a sample of cord blood, there may be special instructions for you to follow. Ask the healthcare worker for any special instructions following this procedure.

What are the risks?

Blood: During a blood draw, a hematoma (blood-filled bump under the skin) or slight bleeding from the puncture site may occur. After a blood draw, a bruise or infection may occur at the puncture site. The person doing this test may need to perform it more than once. Talk to your healthcare worker if you have any concerns about the risks of this test.

Umbilical cord blood: Before your baby is born, umbilical cord blood may be collected by a procedure called percutaneous umbilical cord blood sampling. This procedure is done by inserting a needle through the pregnant mother’s abdomen and into the umbilical cord. Risks of this procedure include bleeding from the puncture site, fetal bradycardia (the baby’s heart rate dropping abnormally low), infection, and thrombosis (blood clot) of the umbilical vein. Another risk of this procedure is an umbilical cord hematoma (a blood-filled pocket that puts pressure on the umbilical cord and can restrict flow of blood to the baby). If you have a medical condition, or are using a medication or supplement that causes excessive bleeding, you are at a higher risk of bleeding from the puncture site. There is a risk that your baby will not survive the procedure. The person doing this procedure may need to perform it more than once. Talk to your healthcare worker if you have any concerns about the risks of having percutaneous umbilical cord blood sampling.

What are normal results for this test?

Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following are considered to be normal results for this test:

  • Adult females, whole blood: 36%-46% (0.36-0.46) [7]:
  • Adult males, whole blood: 41%-53% (0.41-0.53) [7]:
  • Fetal and cord blood [6]:
    • 18 to 20 weeks' gestation: 35.86% +/- 3.29 (0.36 +/- 0.03)
    • 21 to 22 weeks' gestation: 38.53% +/- 3.21 (0.39 +/- 0.03)
    • 23 to 25 weeks' gestation: 38.59% +/- 2.41 (0.39 +/- 0.02)
    • 26 to 30 weeks' gestation: 41.54% +/- 3.31 (0.42 +/- 0.03)
    • Cord Blood: 42%-60% (0.42-0.6)
  • Neonates, 1 day (capillary whole blood): 61% +/- 7.41 (0.61 +/- 0.07) [6]
  • Neonates, 4 days (capillary whole blood): 57% +/- 8.1 (0.57 +/- 0.08) [6]
  • Neonates, 7 days (capillary whole blood): 56% +/- 9.4 (0.56 +/- 0.09) [6]
  • Neonates, 1-2 weeks (capillary whole blood): 54% +/- 8.3 (0.54 +/- 0.08) [6]
  • Neonates, 3-4 weeks (capillary whole blood): 43% +/- 5.7 (0.43 +/- 0.06) [6]
  • Infants, 5-6 weeks (capillary whole blood): 36% +/- 6.2 (0.36 +/- 0.06) [6]
  • Infants, 7-8 weeks (capillary whole blood): 33% +/- 3.7 (0.33 +/- 0.04) [6]
  • Infants, 9-10 weeks (capillary whole blood): 32% +/- 2.7 (0.32 +/- 0.03) [6]
  • Infants, 11-12 weeks (capillary whole blood): 33% +/- 3.3 (0.33 +/- 0.03) [6]
  • Infants, 2 weeks ( whole blood): 41%-65% (0.41-0.65) [6]
  • Infants, 1 month (whole blood): 33%-55% (0.33-0.55) [6]
  • Infants, 2 months (whole blood): 28%-42% (0.28-0.42) [6]
  • Infants, 4 months (whole blood): 32%-44% (0.32-0.44) [6]
  • Infants, 6 months (whole blood): 31%-41% (0.31-0.41) [6]
  • Infants, 9 months (whole blood): 32%-40% (0.32-0.40) [6]
  • Infants, 12 months (whole blood): 33%-41% (0.33-0.41) [6]
  • Infants, 1-2 years (whole blood): 32%-40% (0.32-0.40) [6]
  • Children, 3-5 years (whole blood): 32%-42% (0.32-0.42) [6]
  • Children, 6-8 years (whole blood): 33%-41% (0.33-0.41) [6]
  • Children, 9-11 years (whole blood): 34%-43% (0.34-0.43) [6]
  • Females, 12-14 years (whole blood): 34%-44% (0.34-0.44) [6]
  • Males, 12-14 years (whole blood): 35%-45% (0.35-0.45) [6]
  • Females, 15-17 years (whole blood): 34%-44% (0.34-0.44) [6]
  • Males, 15-17 years (whole blood): 37%-48% (0.37-0.48) [6]

What might affect my test results?

  • Results increased in [6]:
    • Prolonged venous status during venipuncture
    • Strenuous exercise
    • High altitude
  • Results decreased in [6]:
    • Hematocrit is slightly lower between 5 pm and 7 am
    • Hematocrit is up to 5.7% lower in recumbent patients
    • Men aged 65 to 74 years

What follow up should I do after this test?

Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.

References:

[1] Mozaffarian D, Nye R, & Levy WC: Anemia predicts mortality in severe heart failure: the Prospective Randomized Amlodipine Survival Evaluation (PRAISE).. J Am Coll Cardiol 2003; 41:1933-1939.

[2] Gomez JM & Carrera F: What should the optimal target hemoglobin be?. Kidney Int Suppl 2002; 80:39-43.

[3] Henry JB: Clinical Diagnosis and Management by Laboratory Methods, 20th ed. Saunders, 2001.

[4] National Kidney Foundation: Guidelines for the anemia of chronic kidney disease. National Kidney Foundation. New York, New York, USA. 2000. Available from URL: http://www.kidney.org/professionals/kdoqi/guidelines_updates/doqiupan_ii.html. As accessed 7/21/2005.

[5] Collins A, Ma JZ, & Ebben J: Impact of hematocrit on morbidity and mortality. Seminars in Nephrology 2000; 20(4):345-349.

[6] Tietz NW (Ed): Clinical Guide to Laboratory Tests, 3rd ed. W. B. Saunders, Philadelphia, PA, 1995.

[7] Kratz A, Ferraro M, Sluss PM, et al: Case records of the Massachusetts General Hospital: laboratory values. N Engl J Med 2004; 351(15):1549-1563.


Last Updated: 11/4/2014

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