Hematocrit (HCT)


Article Author:
Himel Mondal


Article Editor:
Deepa Budh


Editors In Chief:
Alexandra Caley
Sameh Boktor


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Trevor Nezwek
Radia Jamil
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes


Updated:
6/3/2019 9:59:35 AM

Introduction

The term "hematocrit (HCT)" originated from English “hemato-“ and Greek “krites.” HCT measures the volume of packed red blood cells (RBC) relative to whole blood. Hence, it is also known and reported as a packed cell volume (PCV). It is a simple test to identify conditions like anemia or polycythemia and also to monitor response to the treatment. A glass tube and a centrifuge machine are sufficient to measure HCT. After centrifugation, the component of blood separates into three distinct parts. From below upwards, the layers are - a layer of red blood cells (RBC), a layer of white blood cells(WBC) and platelets, and a layer of plasma at the top. This method of determining HCT by Wintrobe hematocrit tube is known as the “macro-hematocrit” method.[1]  A Wintrobe tube is a narrow glass tube measuring 110-mm-long, with graduation from 0 to 100 mm in both ascending and descending order.   This method has been succeeded by the “micro-hematocrit” method which uses a small capillary tube instead of a Wintrobe hematocrit tube. It requires less quantity of blood as well as less time requirement for the testing procedure. It is beneficial for patients from whom blood collection is difficult (e.g., pediatric patients/hypovolemia). However, the principle of the test remains the same as the “macro-hematocrit” method. HCT calculation is by dividing the lengths of the packed RBC layer by the length of total cells and plasma. As it is a ratio, it doesn’t have any unit. Multiplying the ratio by 100 gives the accurate value, which is the accepted reporting style for HCT. A normal adult male shows an HCT of 40% to 54% and female shows 36% to 48%.[2] Though these two methods are still in use in some settings of primary care and medical teachings, they are widely replaced in the majority of settings by an automated analyzer, where HCT reports get generated along with the complete blood count.  

Specimen Requirements and Procedure

For the macro-hematocrit method, venous blood is taken as a random sample (i.e., no special precautions needed) maintaining proper aseptic precautions. The blood is either collected in a commercially available vacutainer containing ethylenediaminetetraacetic acid (EDTA) or in a vial/test tube with EDTA where vacutainer is not available[3]. For the microhematocrit method, the blood requirement is less, and single finger-prick blood is sufficient. Heparin filled capillary tube may is used to collect blood. However, if there is available blood with anticoagulant for other hematologic tests, a capillary tube without heparin can be used. For measurement of HCT in automated hematologic cell counter, blood with anticoagulant used for CBC is necessary.

Testing Procedures

The macro-hematocrit method uses a Wintrobe hematocrit tube, a centrifuge machine, and a Pasteur pipette. Blood is filled in Wintrobe hematocrit tube up to 100 mm mark by the help of Pasteur pipette. Care is taken not to leave any bubble in the blood column. For this, the tube is filled slowly with the tip of the pipette being always below the highest position of the blood column. Then, the tube gets placed in the centrifuge machine. When testing a single specimen, another blood-filled Wintrobe hematocrit tube is kept on the opposite holder to counterbalance. The spin setting is 3000 rpm for 30 min. After completion of the centrifugation, the tube is taken out, and RBC column height is reported as HCT. During the reporting, special precaution is necessary to omit the buffy coat, which is a combination of WBC and platelets. This layer should not be included in the HCT, as it may lead to false positive results.

For the microhematocrit method, after filling the blood in a capillary tube, the two ends of the tube (commonly 75 mm long, 1 mm diameter) are sealed with clay sealant or heat. Then, it is centrifuged at a rate of 11000 to 12000 rpm for 4 to 5 min. Reading is with the help of the scale on a tube holder or microhematocrit card reader.

The automated analyzer measures the average RBC size and number by the “Coulter principle”[4]. In this method, the size and number of the RBCs is measurable by detecting impedance while the blood passes through a passage between two electrodes.

Interfering Factors

There are several physiological and pathological conditions where the HCT may deviate from its normal range. New-born babies show a high HCT, and it gradually decreases during the neonatal period[5]. Adult male shows higher HCT than an adult female.[6] Pregnant women show lower HCT due to hemodilution. In high altitude, the number of RBC becomes high due to persistent hypoxia; hence, the inhabitant of high altitude shows higher HCT. Methodological variation may provide a minor deviation of HCT tested for the same sample. In the macro-hematocrit method, there is an increased amount of trapped plasma (approximately 2%) in the packed RBC, which may give a higher HCT. This factor becomes minimized in the microhematocrit method, where the amount of trapped plasma is less as the diameter of the capillary tube is less than that of the Wintrobe hematocrit tube. Blood collected from different sources may also show variation. Venous blood shows higher HCT than arterial blood. However, there is no difference in HCT between venous blood and finger prick blood.[7]

Results, Reporting, Critical Findings

Wintrobe hematocrit tube has graduation 0 to 100 from below upwards. Hence, the highest level of packed RBC is the HCT in percentage. For the microhematocrit method, the reading is from the HCT card or scale. However, for these two methods, even without any graduation or scale, the HCT value can be calculated with a simple scale as we compare the length of the RBC column with the total length of the fluid column. The final report is a percentage. HCT, along with RBC count and hemoglobin (Hb) concentration, is used to report other blood indices manually as follows:

The mean corpuscular volume (MCV) calculation uses HCT and RBC count.

  • MCV (fL) = HCT (%) × 10 / RBC count (10^12/L)

Mean corpuscular hemoglobin concentration (MCHC) is calculated with Hb concentration and HCT.

  • MCHC (%) = Hb concentration (g/dL) / HCT (%) × 100

Clinical Significance

In primary health care settings, especially in resource-limited settings, macro-hematocrit and micro-hematocrit methods are two low-cost and simple tests for determining RBC in blood. Clinically, HCT is used to identify anemia and polycythemia along with other parameters (e.g., RBC count, Hb concentration). In anemia, where there are fewer RBCs in the circulating blood relative to the total volume of the blood, the HCT decreases.[8] In polycythemia, there is a higher number of RBCs in the blood; HCT increases. Smokers and chronic obstructive pulmonary disease (COPD) patients also have high HCT due to chronic hypoxia. The increase in HCT increases the viscosity of the blood, so does the peripheral resistance. Hence, patients with higher HCT may have higher blood pressure.

Quality control and Lab Safety

Handling of blood should take place with the maintenance of proper aseptic precautions. The collected blood should be tested as soon as possible after collection. Prolonged storage at the room temperature would result in a change in the shape of the RBCs due to metabolism. After about 6 hours, the chances of hemolysis increase, which would give an erroneous result. In the macro-hematocrit method, the filing of the Wintrobe hematocrit tube requires proper care. In the microhematocrit method, the sealing of the capillary tube should be secure to prevent any leakage. The centrifuge machine should not be opened during the test to avoid erroneous results. The chances of error in the result will increase if the centrifugation is interrupted. Immediately after completion of the rotation, the operator should not open the lid should until after the complete stoppage of the rotation. For reuse of the Wintrobe hematocrit tube, proper cleaning is necessary as any foreign particle inside the tube would be counted either in the RBC column or plasma column.

Enhancing Healthcare Team Outcomes

After the introduction of the automated hematology cell counters, the usage of macro-hematocrit and microhematocrit method is less used nowadays. However, in many resource-poor settings, it is still used for the diagnosis of anemia and polycythemia and monitoring response to treatment. In a rural healthcare facility, it is a more accurate method for identifying anemia than the total RBC count, as chances of error in manual RBC count is very high. The micro-hematocrit method is more acceptable as it requires less amount of blood, and the testing time is very less in comparison to the macro-hematocrit method. Due to the requirement of less amount of blood and less time for the test, it may be useful in a mass survey.


  • Image 10012 Not availableImage 10012 Not available
    Contributed by Shaikat Mondal, MD
Attributed To: Contributed by Shaikat Mondal, MD

Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Hematocrit (HCT) - Questions

Take a quiz of the questions on this article.

Take Quiz
A 58-years-old male patient presents with chief complaints of fatigue and pinpoints rash over the body. Clinical examination reveals pallor, enlarged lymph nodes, swollen gums, and an enlarged liver. The peripheral blood smear shows 32% blast cells. What is the expected hematocrit in this patient if the blood is tested by the macrohematocrit method?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 6-year-old boy with severe pallor requires a quick check of his hematocrit. Which method is most suitable for the measurement of hematocrit in this case?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A clinical pathologist is investigating the different methods of hematocrit measurement. Venous and arterial blood samples are collected from a subject and hematocrit is measured by macrohematocrit method. Which of the following would be the most likely expected finding?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A hematology researcher is calculating different blood indices from a patient's incomplete blood count. He has the hemoglobin concentration and hematocrit value of a patient. Which of the following parameters can he most accurately calculate?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A blood sample was collected at 6 am and tested at 4 pm. The blood was kept at room temperature (30 C) between collection and testing. What changes would be expected in hematocrit (HCT) if the measurement is done by the macrohematocrit method?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 32 weeks pregnant woman was tested for hemoglobin (Hb) level and hematocrit (HCT). What changes are expected in comparison to non-pregnant state?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up

Hematocrit (HCT) - References

References

Fred HL, Maxwell Myer Wintrobe: new history and a new appreciation. Texas Heart Institute journal. 2007;     [PubMed]
Billett HH, Hemoglobin and Hematocrit 1990;     [PubMed]
Bamberg R,Gwyn T,Miller J,Thompson M,Transou P, The effects of over-anticoagulated blood on hematocrit values by the microcentrifuge method. Clinical laboratory science : journal of the American Society for Medical Technology. 2008 Summer;     [PubMed]
Peng L,Wang W,Bai L, Performance evaluation of the Z2 coulter counter for WBC and RBC counting. International journal of laboratory hematology. 2007 Oct;     [PubMed]
Jopling J,Henry E,Wiedmeier SE,Christensen RD, Reference ranges for hematocrit and blood hemoglobin concentration during the neonatal period: data from a multihospital health care system. Pediatrics. 2009 Feb;     [PubMed]
Zeng SM,Yankowitz J,Widness JA,Strauss RG, Etiology of differences in hematocrit between males and females: sequence-based polymorphisms in erythropoietin and its receptor. The journal of gender-specific medicine : JGSM : the official journal of the Partnership for Women's Health at Columbia. 2001;     [PubMed]
Yang ZW,Yang SH,Chen L,Qu J,Zhu J,Tang Z, Comparison of blood counts in venous, fingertip and arterial blood and their measurement variation. Clinical and laboratory haematology. 2001 Jun;     [PubMed]
Malenica M,Prnjavorac B,Bego T,Dujic T,Semiz S,Skrbo S,Gusic A,Hadzic A,Causevic A, Effect of Cigarette Smoking on Haematological Parameters in Healthy Population. Medical archives (Sarajevo, Bosnia and Herzegovina). 2017 Apr     [PubMed]

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of CNS-Public Community Health. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for CNS-Public Community Health, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in CNS-Public Community Health, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of CNS-Public Community Health. When it is time for the CNS-Public Community Health board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study CNS-Public Community Health.