Hematocrit – StatPearls – NCBI Bookshelf

Himel Mondal; Saran Lotfollahzadeh.

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Last Update: January 2, 2023.

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 a 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, and 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.

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

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.

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Figure

Wintrobe hematocrit tube containing components of blood after centrifugation. Contributed by Shaikat Mondal, MD

References

1.

Fred HL. Maxwell Myer Wintrobe: new history and a new appreciation. Tex Heart Inst J. 2007;34(3):328-35. [PMC free article: PMC1995040] [PubMed: 17948084]

2.

Billett HH. Hemoglobin and Hematocrit. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd ed. Butterworths; Boston: 1990. [PubMed: 21250102]

3.

Bamberg R, Gwyn T, Miller J, Thompson M, Transou P. The effects of over-anticoagulated blood on hematocrit values by the microcentrifuge method. Clin Lab Sci. 2008 Summer;21(3):146-50. [PubMed: 18678135]

4.

Peng L, Wang W, Bai L. Performance evaluation of the Z2 coulter counter for WBC and RBC counting. Int J Lab Hematol. 2007 Oct;29(5):361-8. [PubMed: 17824917]

5.

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;123(2):e333-7. [PubMed: 19171584]

6.

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. J Gend Specif Med. 2001;4(1):35-40. [PubMed: 11324238]

7.

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. Clin Lab Haematol. 2001 Jun;23(3):155-9. [PubMed: 11553055]

8.

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. Med Arch. 2017 Apr;71(2):132-136. [PMC free article: PMC5511531] [PubMed: 28790546]

Disclosure: Himel Mondal declares no relevant financial relationships with ineligible companies.

Disclosure: Saran Lotfollahzadeh declares no relevant financial relationships with ineligible companies.

Hematocrit test | Beacon Health System

Overview

A hematocrit (he-MAT-uh-krit) test measures the proportion of red blood cells in your blood. Red blood cells carry oxygen throughout your body. Having too few or too many red blood cells can be a sign of certain diseases.

The hematocrit test, also known as a packed-cell volume (PCV) test, is a simple blood test.

Why it’s done

A hematocrit test is part of a complete blood count (CBC). Measuring the proportion of red blood cells in your blood can help your doctor make a diagnosis or monitor your response to a treatment.

A lower than normal hematocrit can indicate:

• An insufficient supply of healthy red blood cells (anemia)
• A large number of white blood cells due to long-term illness, infection or a white blood cell disorder such as leukemia or lymphoma
• Vitamin or mineral deficiencies
• Recent or long-term blood loss

A higher than normal hematocrit can indicate:

• Dehydration
• A disorder, such as polycythemia vera, that causes your body to produce too many red blood cells
• Lung or heart disease

How you prepare

The hematocrit is a simple blood test. You won’t need to fast before the test or make other preparations.

What you can expect

The blood sample is generally drawn with a needle from a vein in your arm. You may feel some tenderness at the site, but you’ll be able to resume normal activities afterward.

Results

Results from your hematocrit test are reported as the percentage of your blood volume that’s composed of red blood cells. Normal ranges vary substantially with race, age and sex. The definition of normal red-blood cell percentage also varies from one medical practice to another.

Generally, a normal range is considered to be:

• For men, 38.3 to 48.6 percent
• For women, 35.5 to 44.9 percent

For children ages 17 and younger, the normal range varies by age and sex.

Your hematocrit test provides just one piece of information about your health. Talk to your doctor about what your hematocrit test result means in light of the symptoms you’re experiencing and the results of other diagnostic tests.

Accuracy of test results

A number of factors can affect the outcome of a hematocrit test and yield inaccurate or misleading results, including:

• Living at a high altitude
• Pregnancy
• Significant recent blood loss
• Recent blood transfusion
• Severe dehydration

Your doctor will take into account possible complicating factors when interpreting the results of your hematocrit test. Your doctor may want to repeat the hematocrit test and do other blood tests if results provide conflicting or unexpected information.

Last Updated: December 14th, 2021

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Hematocrit – Blood test – Deciphering tests online

Synonyms : hematocrit, HCT, Ht, Crit, packed cell volume, PCV

What is hematocrit?

Hematocrit is the percentage (%) of the total blood volume that is made up of erythrocytes, that is, it is the ratio of erythrocytes to blood plasma.

Decipher “Biochemical analysis of blood”
Decipher “General analysis of urine”

Erythrocytes carry oxygen throughout the body. Having too many or too few red blood cells in the blood can be a sign of certain medical conditions.

The hematocrit value is often used to assess the severity of anemia, due to which it can drop to 15-25%. Hematocrit should not be assessed immediately after a blood transfusion or blood loss, as this may cause a falsely high or falsely low result.

Measurement units

Hematocrit (Ht) is expressed as a percentage (%) of the total blood volume or in liters per liter (l/l) – the corresponding proportion of formed elements in 1 liter of blood (480 ml of cells in 1 liter of blood = 0, 48 liter/liter = 48%).

Under normal conditions, there is a linear relationship between hematocrit and hemoglobin concentration.

Normal hematocrit

Normal hematocrit values ​​may vary slightly depending on age, gender, pregnancy, place of residence, use of different diagnostic methods.

The following hematocrit values ​​are generally considered normal:

• Adult men: 42-54%
• Adult women: 38-46%0032

For residents of high altitudes, hematocrit norms increase as the altitude at which people live increases. This is a consequence of the lower concentration of oxygen in the atmosphere, which requires more red blood cells to provide the body with the necessary amount of oxygen.

Hematocrit can be low or high for various reasons. But it should be remembered that its level in some cases may be assessed incorrectly (with loss of blood, during transfusion, in the mountains). According to the study, moving from a supine position to a sitting position can cause clinically significant increases in hemoglobin, hematocrit, and red blood cell count.

Hematocrit during pregnancy

Blood volume increases during pregnancy. But the volume of plasma increases more than the volume of erythrocytes, which leads to relative anemia. There is a physiological decrease in the number of erythrocytes (RBC), as well as the level of hemoglobin (Hb) and hematocrit (Hct). Different laboratories may have different hematocrit reference values. Below is the approximate content of hematocrit in the blood during pregnancy.

In the first trimester of pregnancy, hematocrit is normally 31-41%. By 6-12 weeks, the volume of blood plasma has already increased by approximately 10-15%. The blood thins, and the concentration of cells in it decreases. Therefore, in a pregnant woman, a slight decrease in hematocrit and hemoglobin is allowed by the end of the first / middle of the second month of pregnancy. If the indicator falls below the norm, then we can talk about the manifestation of anemia.

In the second trimester, the volume of circulating blood steadily increases. The risk of developing iron deficiency anemia at this time increases. Therefore, obstetrician-gynecologists attach particular importance to the mandatory regular monitoring of the expectant mother and hematocrit indicators. Reference hematocrit values ​​in the second trimester are 30-39%.

Hematocrit reaches its lowest level in the third trimester. From 30 to 34 weeks of pregnancy, the fastest rate of increase in circulating blood volume is observed, after which this volume changes slightly until delivery. Hematocrit peaks at 33 weeks. Hematocrit below the normal level (28-40%) should be considered as a pathology.

Hematocrit values ​​above normal during pregnancy are also classified as pathological.

Normal hematocrit in children

In newborns and especially premature babies, high hematocrit values ​​are normal. If the hematocrit level in a blood test from a vein exceeds 65%, then polycythemia is diagnosed (an increased level of red blood cells). Closer to the age of three months, the hematocrit drops. Reference values ​​for hematocrit are approximately 30-44%, depending on the age of the child.

Reduced or increased hematocrit in a child with minor deviations from the norm, most often caused by the influence of external factors. If these deviations are significant, then it is necessary to look for the causes of such a state.

Hematocrit above normal

A high hematocrit may reflect an absolute increase in red blood cells or a decrease in plasma volume. An increase in hematocrit means that the blood thickens, which means that the risk of blood clots increases. This causes oxygen deficiency of the organ in which the thrombus has formed, and, accordingly, a violation of its functions (stroke, heart attack).

Causes of increased hematocrit:

• Dehydration (for burns, diarrhea, taking diuretics). With sufficient fluid intake, the hematocrit returns to normal.
• Diseases of the heart and lungs. The body tries to compensate for the lack of oxygen in the blood by producing more red blood cells.
• Smoking, living high above sea level (compensation for a decrease in the level of oxygen in the body)
• Neoplasms in the kidneys, accompanied by increased production of erythropoietin.
• Polycythemia vera (polycythemia vera) is a rare disorder that causes an abnormal production of red blood cells.

High hematocrit during pregnancy

Elevated hematocrit in pregnancy signals blood clotting, increasing the burden on the cardiovascular system and increasing the likelihood of blood clots.

High hematocrit may be a sign of preeclampsia (preeclampsia).

High hematocrit in a child

If, when determining the results of a blood test, the hematocrit is very high (more than 65%) in a newborn child, it means that the baby was in a state of hypoxia. That is, the child experienced oxygen deficiency during the prenatal period or during childbirth. The future development of the baby depends on the duration of the hypoxia period, because during oxygen starvation, the blood supply to the brain is disturbed.

At an older age, the same pathological conditions as in adults can become the reasons for the increase.

Hematocrit below normal

A low hematocrit reflects a low number of circulating red blood cells and is an indication of reduced oxygen carrying capacity. In this condition, patients have shortness of breath, a constant feeling of fatigue, palpitations, pale skin, hair loss. With a decrease in hematocrit, anemia is diagnosed.

Reasons for low hematocrit:

• Significant blood loss (due to trauma, chronic bleeding).
• Deficiency of nutrients in the body (iron, folic acid, vitamins B12, B6).
• Increased destruction of red blood cells (hemolytic anemia, sickle cell anemia).
• Bone marrow disorders (aplastic anemia, cancer, chemotherapy).
• Kidney disease resulting in decreased production of erythropoietin, a hormone that stimulates the bone marrow to produce red blood cells.

Low hematocrit during pregnancy

A slight decrease in hematocrit due to increased blood volume is normal during pregnancy. With a decrease in hematocrit below the reference values, one speaks of anemia.

In 90% of cases, the cause of low hematocrit during pregnancy is iron deficiency anemia. The state of health of a pregnant woman with a low hematocrit worsens, since the cells of all organs experience oxygen starvation (hypoxia), the alkaline balance is disturbed. You may experience fatigue, weakness, headache, palpitations and shortness of breath. The heart and blood vessels work in an increased load mode, the work of other organs and systems is disrupted.

Low hematocrit in a child

A decrease in hematocrit in children may be due to malnutrition (lack of nutrients) and is also observed with a significant growth spurt. These changes are easily correctable.

In children over 1 year of age and adolescents, acquired types of anemia are more common, especially iron deficiency anemia. In term infants under 6 months of age, iron deficiency is an unlikely cause of anemia.

Deciphering a blood test on the analyzer – Article in Yekaterinburg

In modern hematological analyzers, the ability to decipher from 5 to 24 blood parameters is implemented:

• WBC (white blood cells – white blood cells, leukocytes). The indicator characterizes the absolute content of leukocytes.
• RBC (red blood cells – red blood cells, erythrocytes) shows the absolute content of erythrocytes in the blood.
• HGB (Hb, hemoglobin, hemoglobin) — the concentration of hemoglobin in whole blood.
• HCT (hematocrit, hematocrit). Hematocrit determines the ratio of the volume of formed elements to plasma.
• PLT (platelets, platelets) – absolute number of platelets

Erythrocyte indices

• MCV – average volume of erythrocyte in microns or fl. Using the analysis, you can determine the presence of microcytosis, normocytosis, macrocytosis.
• MCH is the average amount of hemoglobin in an erythrocyte in absolute units. The analysis indicates the color index.
• MCHC is the average concentration of hemoglobin in one erythrocyte, i.e. its degree of saturation with hemoglobin.

Platelet indices

• MPV (mean platelet volume) – the average number of platelets
• PDW – characterizes platelet heterogeneity, i. e. their relative width of distribution in volume.
• PCT (platelet crit) – thrombocrit – the percentage of whole blood volume occupied by platelets.

Leukocyte indices

• LYM% (LY%) (lymphocyte) — percentage of lymphocyte concentration.
• LYM# (LY#) (lymphocyte) — absolute number of lymphocytes.
• MXD% is the relative percentage of a mixture consisting of monocytes, basophils and eosinophils.
• MXD# is the absolute amount of a mixture consisting of monocytes, basophils and eosinophils.
• NEUT% (NE%) (neutrophils) – percentage of neutrophils.
• NEUT# (NE#) (neutrophils) — absolute number of neutrophils.
• MON% (MO%) (monocyte) – percentage of monocytes
• MON# (MO#) (monocyte) – absolute number of monocytes
• EO% – relative percentage of eosinophils.
• EO# is the absolute number of eosinophils.
• BA% – relative percentage of basophils.
• BA# is the absolute number of basophils.
• IMM% – relative percentage of immature granulocytes.
• IMM# is the absolute number of immature granulocytes.
• ATL% – relative percentage of atypical lymphocytes.
• ATL# is the absolute number of atypical lymphocytes.
• GR% – relative percentage of granulocytes.
• GR# is the absolute number of granulocytes.

RBC indices

• RBC/HCT – mean volume of red blood cells.
• HGB/RBC is the average amount of hemoglobin in an erythrocyte.
• HGB/HCT — average saturation of erythrocyte hemoglobin.
• RDW – Red cell Distribution Width – “the width of the red blood cell distribution.” Characterizes the heterogeneity of erythrocytes.
• RDW-SD is the standard deviation of the distribution width of erythrocytes by volume.
• RDW-CV – coefficient of variation in the relative width of the distribution of erythrocytes by volume.
• P-LCR is a coefficient indicating the number of large platelets.