What is hct on lab results: Hematocrit Test: MedlinePlus Medical Test

07.12.202113.07.2023 by alexxlab

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Hematocrit – StatPearls – NCBI Bookshelf

Himel Mondal; Saran Lotfollahzadeh.

Author Information and Affiliations

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: Uses, Procedure, and Results

What is hematocrit?

Hematocrit is the percentage of red blood cells in the total blood volume. Red blood cells are vital to your health. Imagine them as the subway system of your blood. They transport oxygen and nutrients to various locations in your body. For you to stay healthy, your body needs to have the correct proportion of red blood cells.

Your doctor may order a hematocrit, or Hct, test if they think you have too few or too many red blood cells.

A hematocrit test can help your doctor diagnose you with a particular condition, or it can help them determine how well your body is responding to a certain treatment. The test can be ordered for a variety of reasons, but it’s most often used to test for:

anemia
leukemia
dehydration
dietary deficiencies

If your doctor orders a complete blood count (CBC) test, the hematocrit test is included. Other tests in a CBC are a hemoglobin and reticulocyte count. Your doctor will look at your overall blood test results to gain an understanding of your red blood cell count.

Learn more: CBC (complete blood count) »

First you will receive a blood test. Afterward, it will be sent to a laboratory for evaluation.

Blood sample

A medical provider will need a small sample of blood to test your hematocrit. This blood can be drawn from a finger prick or taken from a vein in your arm.

If the hematocrit test is part of a CBC, a lab technician will draw blood from a vein, typically from the inside of your elbow or from the back of your hand. The technician will clean the surface of your skin with an antiseptic and place an elastic band, or tourniquet, around your upper arm to help the vein swell with blood.

They’ll then insert a needle in the vein and collect a blood sample in one or more vials. The technician will remove the elastic band and cover the area with a bandage to stop the bleeding. A blood test can be slightly uncomfortable. When the needle punctures your skin, you might feel a prick or pinching sensation. Some people also feel faint or lightheaded when they see blood. You may experience minor bruising, but this will clear up within a few days. The test will take only a few minutes, and you can resume everyday activities after it’s finished. Your sample will be sent to a lab for analysis.

Evaluation

In the laboratory, your hematocrit is evaluated using a centrifuge, which is a machine that spins at a high rate to cause the contents of your blood to separate. A lab specialist will add a special anticoagulant to keep your blood from clotting.

When the test tube is taken out of the centrifuge, it will have settled into three parts:

red blood cells
anticoagulant
plasma, or the fluid in your blood

Each component will settle in a different part of the tube, with the red blood cells moving to the bottom of the tube. The red blood cells are then compared to a guide that tells what proportion of your blood they make up.

While the laboratory that tests the blood sample may have its own ranges, generally accepted ranges for hematocrit depend on your gender and age. Typical ranges are as follows:

adult men: 38. 8 to 50 percent
adult women: 34.9 to 44.5 percent

Children ages 15 and under have a separate set of ranges, as their hematocrit levels change rapidly with age. The specific lab that analyzes the results will determine the normal hematocrit range for a child of a certain age.

If your hematocrit levels are too low or too high, it can indicate various problems.

Low hematocrit levels may be a sign of:

bone marrow diseases
chronic inflammatory disease
deficiencies in nutrients such as iron, folate, or vitamin B-12
internal bleeding
hemolytic anemia
kidney failure
leukemia
lymphoma
sickle cell anemia

High hematocrit levels can indicate:

congenital heart disease
dehydration
kidney tumor
lung diseases
polycythemia vera

Before getting the test, let your doctor know if you’ve recently had a blood transfusion or are pregnant. Pregnancy can decrease your blood urea nitrogen (BUN) levels due to increased fluid in your body. A recent blood transfusion can also affect your results. If you live at a high altitude, your hematocrit levels tend to be higher due to reduced amounts of oxygen in the air.

Your doctor will likely compare the results of your hematocrit test to the other parts of the CBC test and your overall symptoms before making a diagnosis.

A hematocrit test is not associated with any major side effects or risks. You may have some bleeding or throbbing at the site where the blood is drawn. Let your doctor know if you experience any swelling or bleeding that doesn’t stop within a few minutes of pressure being applied to the puncture site.

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Red blood cells (RBCs) are red blood cells that contain the protein hemoglobin. The average lifespan of erythrocytes is 110-130 days. The main function of red blood cells is to carry oxygen from the lungs to other organs and tissues. An increase in the number of red blood cells (erythrocytosis) occurs with tissue hypoxia, polycystic kidney disease, renal artery stenosis, hydronephrosis, tumors, etc. A decrease in the number of red blood cells (erythrocytopenia) occurs after blood loss, with anemia, after radiation exposure, with increased breakdown of red blood cells, with diseases of the kidneys and liver, against the background of infectious diseases.

Hemoglobin (Hb) increases with dehydration, with an increase in the number of red blood cells. The concentration of hemoglobin decreases with anemia and with hyperhydration.

Hematocrit (HCT) is an indicator that is determined by calculating the ratio of the volume of erythrocytes to the volume of the liquid part of the blood. Hematocrit increases with an increase in the number of red blood cells, with burn disease and dehydration of the body. HCT decreases with anemia, overhydration, pregnancy.

Mean cell volume (MCV) is a measure of the average volume of the entire population of red blood cells. According to this indicator, the doctor determines the type of anemia (normocytic, microcytic and macrocytic). A decrease in MCV is more common in iron deficiency anemia, and an increase in B12 deficiency anemia or folate deficiency anemia.

Mean erythrocyte hemoglobin (MCH) is an indicator of the average content of hemoglobin protein in 1 erythrocyte. Analogue of the obsolete color index (CPU). According to this indicator, the doctor divides anemia into normochromic, hypochromic and hyperchromic. MCH decreases with iron deficiency anemia, porphyria, and increases with macrocytic anemia.

Average concentration of hemoglobin in erythrocytes (MCHC) – the indicator reflects the saturation of erythrocytes with hemoglobin. MCHC increases with spherocytosis, cold agglutination of erythrocytes, after chemotherapy, decreases with hemoglobinopathies, anemia of chronic disease, iron deficiency anemia.

Distribution of erythrocytes by volume (RDW CV) – the indicator reflects the degree of anisocytosis of erythrocytes (change in the size of an erythrocyte). An increase in RDW occurs with a combination of red blood cells of different sizes (for example, normocytes and microcytes).

Platelets (PLT) are nuclear-free small blood cells that are involved in the formation of blood clots in normal conditions (in case of damage to the vessel) and in pathology (when an atherosclerotic plaque is “opened”). The number of platelets increases with increased physical exertion, after surgical interventions, against the background of oncological diseases, in acute and chronic inflammatory processes in the body. A decrease in the number of platelets occurs with bacterial and viral infections, pregnancy, enlarged spleen, autoimmune diseases, etc.

Mean platelet volume (MPV) is a measure of the average volume of the entire population of platelets. An increase in MPV is observed in patients with idiopathic thrombocytopenic purpura, hyperthyroidism, diabetes mellitus, smokers, and alcohol abuse.