Hematocrit





Definition

The hematocrit is a test that measures the percentage of blood that is comprised of red blood cells.


Purpose

The hematocrit is used to screen for anemia, or is measured on a person to determine the extent of anemia. An anemic person has fewer or smaller than normal red blood cells. A low hematocrit, combined with other abnormal blood tests, confirms the diagnosis. The hematocrit is decreased in a variety of common conditions including chronic and recent acute blood loss, some cancers, kidney and liver diseases, malnutrition, vitamin B 12 and folic acid deficiencies, iron deficiency, pregnancy, systemic lupus erythematosus, rheumatoid arthritis and peptic ulcer disease. An elevated hematocrit is most often associated with severe burns, diarrhea, shock, Ad dison's disease, and dehydration, which is a decreased amount of water in the tissues. These conditions reduce the volume of plasma water causing a relative increase in RBCs, which concentrates the RBCs, called hemoconcentration. An elevated hematocrit may also be caused by an absolute increase in blood cells, called polycythemia. This may be secondary to a decreased amount of oxygen, called hypoxia, or the result of a proliferation of blood forming cells in the bone marrow (polycythemia vera).

Critically high or low levels should be immediately called to the attention of the patient's nurse or doctor. Transfusion decisions are based on the results of laboratory tests, including the hematocrit. Generally, transfusion is not considered necessary if the hematocrit is above 21%. The hematocrit is also used as a guide to how many transfusions are needed. Each unit of packed red blood cells administered to an adult is expected to increase the hematocrit by approximately 3% to 4%.


Precautions

Fluid volume in the blood affects hematocrit values. Accordingly, the blood sample should not be taken from an arm receiving IV fluid or during hemodialysis. It should be noted that pregnant women have extra fluid, which dilutes the blood, decreasing the hematocrit. Dehydration concentrates the blood, which increases the hematocrit.

In addition, certain drugs such as penicillin and chloramphenicol may decrease the hematocrit, while glucose levels above 400 mg/dL are known to elevate results. Blood for hematocrit may be collected either by finger puncture, or sticking a needle into a vein, called venipuncture. When performing a finger puncture, the first drop of blood should be wiped away because it dilutes the sample with tissue fluid. A nurse or phlebotomist usually collects the sample following cleaning and disinfecting the skin at the site of the needle stick.


Description

Blood is made up of red blood cells, white blood cells (WBCs), platelets, and plasma. A decrease in the number or size of red cells also decreases the amount of space they occupy, resulting in a lower hematocrit. Conversely, an increase in the number or size of red cells increases the amount of space they occupy, resulting in a higher hematocrit. Thalassemia minor is an exception in that it usually causes an increase in the number of red blood cells, but because they are small, it results in a decreased hematocrit.

The hematocrit may be measured manually by centrifugation. A thin capillary tube called a microhematocrit tube is filled with blood and sealed at the bottom. The tube is centrifuged at 10,000 RPM (revolutions per minute) for five minutes. The RBCs have the greatest weight and are forced to the bottom of the tube. The WBCs and platelets form a thin layer, called the buffy coat, between the RBCs and the plasma, and the liquid plasma rises to the top. The height of the red cell column is measured as a percent of the total blood column. The higher the column of red cells, the higher the hematocrit. Most commonly, the hematocrit is measured indirectly by an automated blood cell counter. It is important to recognize that different results may be obtained when different measurement principles are used. For example, the microhematocrit tube method will give slightly higher results than the electronic methods when RBCs of abnormal shape are present because more plasma is trapped between the cells.


Aftercare

Discomfort or bruising may occur at the puncture site. Pressure to the puncture site until the bleeding stops reduces bruising; warm packs relieve discomfort. Some people feel dizzy or faint after blood has been drawn, and lying down and relaxing for awhile is helpful for these people.


Risks

Other than potential bruising at the puncture site, and/or dizziness, there are no complications associated with this test.


Normal results

Normal values vary with age and sex. Some representative ranges are:

  • at birth: 42-60%
  • six to 12 months: 33-40%
  • adult males: 42-52%
  • adult females: 35-47%

Resources

BOOKS

Chernecky, Cynthia C. and Barbara J. Berger. Laboratory Tests and Diagnostic Procedures. 3rd ed. Philadelphia: W. B. Saunders Company, 2001.

Kee, Joyce LeFever. Handbook of Laboratory and Diagnostic Tests. 4th ed. Upper Saddle River, NJ: Prentice Hall, 2001.

Kjeldsberg, Carl R. Practical Diagnosis of Hematologic Disorders. 3rd ed. Chicago: ASCP Press, 2000.


ORGANIZATIONS

American Association of Blood Banks. 8101 Glenbrook Road, Bethesda, Maryland 20814. (301) 907-6977. Fax: (301) 907-6895. http://www.aabb.org .

OTHER

Uthman, Ed. Blood Cells and the CBC. 2000 [cited February 17, 2003]. http://web2.iadfw.net/uthman/blood_cells.html .


Victoria E. DeMoranville
Mark A. Best

User Contributions:

kifah
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Feb 21, 2006 @ 3:03 am
i want to ask question why centrifuge the hematocrit for only five minute

thank you
Sehar Raza
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Jan 22, 2008 @ 12:12 pm
i want to ask question why centrifuge the hematocrit for only five minute
Vivian
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Aug 14, 2008 @ 6:06 am
Why when the blood glucose level increase the hematocrit is decrease and when hematocrit increase then the blood glucose level decrease?
HENRY
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Nov 6, 2008 @ 12:00 am
please after test of hematocrit i got 51.2 am henry from spain am 23 years is it ok to my body....thanks i need reply.BYE
Cleo Pease
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May 24, 2009 @ 10:10 am
I'm a student LPN and doing a case study. Have a pt who has low RBC and hemocrit. Hemoglobin is normal. Pt has liver cancer and metastasis to bones. I'm trying to find a more definite reason for these low levels. Any help I'd appreciate it.

Thank you
Cleo
Cecille
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Nov 23, 2009 @ 7:07 am
I want to donate blood but test result showed that my hematocrit is below range by 1 point. How can i increase my hematocrit so that i can donate blood... thank you
gee1970
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Dec 28, 2009 @ 8:08 am
my wife is 7 months pregnant and has a hematocrit (PCV) of 29% with feverish feelings and headache, pls explain to me is it associated
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Oct 3, 2010 @ 4:16 pm
what to for a five months pregnancy of hematocrit pvc test of 25%
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May 27, 2011 @ 11:23 pm
basic and informative and also easy to understand.
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May 31, 2011 @ 4:04 am
I want to know hos some drugs like penicillin or chloramphenicol can affect the hematocrit
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Aug 11, 2011 @ 11:11 am
may i know manual (Microhematocrit) method packed cell volume detection,thank you
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Oct 1, 2011 @ 8:08 am
Hi,

I just got discharged from Hospital after Dengue Fever. Twice blood tranfusions were done to increase the Blood Platlet counts. Now although the Platlets have recovered to normal level of 180K, but PCV value is also increased to 46.1
I am confused as to what is normal level of PCV, as the Lab says it should be within 39 to 46. I am unaware of my normal PCV value. However I remember my Hb count was 16, around one year back when I donated blood. So is there a direct correlation o high Hb count with high PCV value.


Regards
Harish
Martin Kalumbi
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Jan 17, 2012 @ 3:15 pm
May i know factors which can falsely elevate or reduce manual PCV?
Troy
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Apr 18, 2012 @ 11:11 am
Why when the blood glucose level increase the hematocrit is decrease and when hematocrit increase then the blood glucose level decrease?
Osas
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Jul 12, 2012 @ 1:13 pm
I am pregnant, and my PVC is 28 what is the cause, and what i do to increased it?
anna
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Sep 14, 2012 @ 2:14 pm
I wanted to give plasma but my hematocrit was too low by 1 point. What can I do to safely increase it? Thank you.
Jazz
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Oct 9, 2012 @ 8:20 pm
What are the ways to perform and hematocrit test and the equipment needed?
Frank
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Oct 30, 2012 @ 8:08 am
a pregnant woman with 27 PVC, please what could be danger in her life and how does she come out it?
Rene j morin
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Oct 30, 2012 @ 6:18 pm
I have polysistic kidney disease. My latest test was 33.6 hemotrocit.Can I increase this number by diet such as iron rich food such as liver or clams? Thank you Rene Morin
philip ibonye
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Nov 2, 2012 @ 2:02 am
i have an eleven+ month old son, since 2 weeks he has falling sick having high fevers,several test has been run and the doctors keep saying he has infection that the blood PCV level is high, recently we were told that his WBC are more than his RBC, he has been on antibiotics and anti malaria almost every month, what advice can you give please.
Oby
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Nov 15, 2012 @ 2:14 pm
My pcv is30 percent? What does it mean and what do I do?
Adeosun
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Dec 28, 2012 @ 10:10 am
I'm pregnant and my pcv is 32percent is it ok or normal if is not what should i take to correct it pls i need an urgent reply thanks.
almas
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Feb 26, 2013 @ 4:04 am
what is haematocrit and mine is 31.5 so what needs to be done
Nenye
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Mar 15, 2013 @ 4:16 pm
Am in my nine months pregnant and my pcv 30%,what can i do
mrs kelechi
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Apr 29, 2013 @ 8:08 am
i am pregnant and went for my pvc test, just to find out that my pvc is 24percent, is it too poor for delivery or is it ok? what do i do?
Oby Ofoegbu
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May 10, 2013 @ 8:08 am
Hello, my hemoglobin is 7 and my Hematocrit/PCV is 20%. Is it abnormal and should I be worried? I am a 39 year old female
TaiwoAbiodun
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Aug 6, 2013 @ 4:04 am
Pls how can I improve my PVC am six month pregnant and my PVC is 30% which I know is not good for me. Pls I need help urgently. Thanks.
stella
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Aug 15, 2013 @ 7:07 am
i am 36 weeks pregnant, I take my routine drugs and eat healthy. My last PCV test was 35% at 32 weeks but at 36 I'm told that my PCV is 32%. Pls how can I improve my PCV? Tnx.
bolanle
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Sep 30, 2013 @ 12:12 pm
I want to a question, pls am 8month pregnant my PCV is 32%.what do I need to do to increase it.Reply soonest pls.
stacy
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Oct 16, 2013 @ 1:13 pm
I have. Critical high HCT 51.8 what does this mean?
Oby E
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Nov 13, 2013 @ 9:09 am
Question--i am 30 weeks pregnant and my pcv is 29%,want to know if its ok for delivery..and if not what can I do to increase it..please what's the normal pcv level that must be attained before delivery
jummy
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Dec 7, 2013 @ 4:04 am
Am 37 weeks pregnant and my pcv was 29%,and the doctor said it was low. Pls how can I increase the blood level and peradvance I went into labour, what is the risk of delivery.
Aderemi
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Dec 8, 2013 @ 5:05 am
I am 30-33 weeks(My LMP was 17th April 2013 snd today is 08/12/2013)My scan results keeps showing 30 weeks)but my PCV level is 27percent)pls am I okay?I hope I am good with it?pls respond quickly.
Murja
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Dec 10, 2013 @ 1:13 pm
What is the nomal pcv for a pregnant women.pls i need ugent answer.
nikky
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Dec 18, 2013 @ 8:08 am
Am in my 7th month pregnancy and My blood pcv is 28%,is it ok?
lizz
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Jan 27, 2014 @ 9:21 pm
Please Am 8 months pregnant and my pcv is 32% Please how can I improve it
afolasade
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Mar 27, 2014 @ 8:08 am
Am in my 17wks pregancy and my pvc is 28%,please how can i improve it.
pouliwe bennair
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Apr 25, 2014 @ 6:18 pm
What does prolonged bleeding time signify and also the complications in blood transfusion and also the aspect of homeostasis does in clotting time assess.
Laide
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Jun 9, 2014 @ 2:14 pm
I am almost six month pregnant my PCV is 30% is it ok any precaution and how do I increase it if need be.
benneth
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Aug 21, 2014 @ 8:08 am
3 months pregnant and pcv is 32% is it very low , ok ;if too low how can i increase

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