Hematocrit test is a clinical study that allows you to obtain information about the ratio of the volume of red blood cells and the liquid part of the blood. Reflects the level of oxygen exchange between the lungs and tissues of the body, the degree of hemoconcentration. Hematocrit examination is part of a general blood test. The results are used for the diagnosis and monitoring of anemia and polycythemia, evaluating the effectiveness of therapeutic measures, in particular blood transfusions, determining the degree of dehydration, thickening or thinning of blood, determining the need for blood transfusion. Blood sampling for analysis is performed from a vein or capillaries. The hematocrit value is determined using standard centrifugation or in an automatic hematology analyzer. Reference values for men are 39-51%, for women – 35-47%. The timing of the analysis does not exceed a day.
Hematocrit is a laboratory indicator of the total blood count, which reflects the ratio of the volume of red blood cells to the volume of plasma. The final value is expressed as a percentage and indicates the ability of the blood to carry oxygen. An increase in hematocrit is determined in cases when the level of red blood cells in the blood increases or the amount of its liquid part decreases. Such conditions can be triggered by both diseases, for example, polycythemia, and physiological conditions. Hematocrit decreases with a decrease in the level of red blood cells and the intake of a large amount of fluid, which increases the volume of plasma. Changes of this nature occur, for example, with blood loss followed by the introduction of saline.
The hematocrit index depends not only on the concentration of red blood cells, but also on their size. So, with iron deficiency anemia, the size of red blood cells decreases, hematocrit decreases. In clinical and laboratory practice, to determine this indicator, blood is taken from capillaries, less often from a vein. The result is expressed as a percentage or a fractional number reflecting the concentration of red blood cells – l/L. The examination procedure is performed in two ways – hematocrit can be determined using standard centrifugation or using a hematological analyzer. The test results are used in general therapeutic practice, in pediatrics, hematology, intensive care, surgery and other fields of medicine.
Hematocrit test is part of the general blood test. The study is performed during preventive examinations for the purpose of early detection of diseases and conditions accompanied by anemia, dehydration, polycythemia, polyglobulia, bleeding (hidden). Purposefully, the analysis is prescribed if anemia is suspected, the symptoms of which are weakness, fatigue, headache and dizziness, objectively determined pallor and dryness of the skin, brittle nails, weight loss. The results of the hematocrit make it possible to identify the pathology, determine the degree of its severity and track the effectiveness of treatment, but do not indicate its cause.
Other indications for a general blood test with the determination of hematocrit include primary and secondary polycythemia. In these diseases, there is an increase in the number of red blood cells in the blood. The hematocrit test is performed in primary polycythemia, when an increase in the concentration of erythrocytes is associated with an increase in their production in the red bone marrow, and in secondary polycythemia associated with diseases of the cardiovascular and respiratory system, kidney pathologies, tumors. The determination of the hematocrit value is used in the diagnosis of dehydration conditions, bleeding, to address the need for blood transfusion and the introduction of saline solution, to monitor the effectiveness of these procedures.
A hematocrit test without examining the level of red blood cells and their morphology does not provide enough information to identify various hematological disorders. To diagnose anemia and polycythemia, it is necessary to determine several indicators, including the number of red blood cells, hemoglobin, ferritin, serum iron, transferrin, erythropoietin, and OHSS. In clinical practice, the study of hematocrit has become widespread due to the cost-effectiveness of the procedure, its reproducibility and accessibility. These three criteria are especially important in primary, including preventive examinations of large groups of patients.
Preparation for analysis and material collection
When performing a general blood test with the determination of hematocrit, blood is taken in the morning, on an empty stomach. It is not necessary to carry out special preparation for the sampling procedure, but it is important to follow several recommendations: the day before the study, you should refrain from drinking alcohol, at least 8-12 hours should pass after eating, smoking and physical exertion should be stopped in half an hour, and stress factors should be avoided. During a conversation with a doctor, it is worth informing him about the medications taken so that their possible effect on the hematocrit index is taken into account when interpreting the results. There are no restrictions on the use of clean water.
Most often, blood for hematocrit examination is taken from the ring finger. The procedure is performed using a scarifier pen or a lancet. If venous blood sampling is recommended by the doctor, then a puncture of the ulnar vein is performed. After taking the biomaterial is mixed with an anticoagulant to prevent the clotting process. In laboratories, two methods are used to determine hematocrit – standard centrifugation and with the use of a hematological analyzer. Their essence lies in the fact that in the process of centrifugation (rapid rotation), heavier and bulkier particles (red blood cells) settle to the bottom. Then the height of the lower layer is determined and its percentage ratio to the total height of the liquid is calculated. The preparation of the results of this study takes no more than 1 working day.
Hematocrit indicators are expressed as percentages or fractions. The values of the norm depend on age and gender. For men, they range from 39 to 51% or from 0.39 to 0.51. In women, the hematocrit is lower, since the blood is renewed more often, the norm values are from 35 to 47% or from 0.35 to 0.47. In children, the indicator is determined by age:
- from birth to 7 days – 42-66%;
- from 7 days to 1 month – 36-63%;
- from 1 to 6 months – 30-48%;
- from 6 months to 2 years – 33-39%;
- from 2 to 6 years – 33-39%;
- from 6 to 12 years – 35-45%;
- from 12 to 15 years – 36-49%;
- from 15 to 18 years – 37-49% for boys, 36-46% for girls.
A physiological change in the hematocrit value is observed during pregnancy, from the 20th week the indicators gradually decrease, and before childbirth they rise to normal values. Some increase in the indicator is possible with oxygen starvation caused by frequent smoking, staying in high-altitude areas.
Increasing the value
The reason for the increase in hematocrit may be an increase in the volume of red blood cells in the blood. Changes of this nature are observed in diseases accompanied by an increase in the number or size of red blood cells – with redistributive and true erythrocytosis, primary and secondary polycythemia, compensatory reactions of the cardiovascular system. Another reason for an increase in hematocrit is a decrease in the liquid part of the blood. Dehydration can be caused by burn disease, peritonitis, profuse diarrhea, vomiting, intestinal obstruction, hyperhidrosis.
Reducing the value
One of the reasons for the decrease in hematocrit values is erythropenia – a decrease in the number of red blood cells in the blood. The level of red blood cells drops when their production in the red bone marrow is disrupted with anemia, leukemia, prolonged use of cytostatics and antitumor drugs. Sometimes the number of red blood cells in the blood is reduced due to their intense destruction. Such changes occur with hemolytic anemia, poisoning with hemolytic poisons, typhoid fever, malaria. After bleeding and restoring the volume of circulating blood, a temporary decrease in the level of red blood cells and hematocrit values is also determined by saline.
Another reason for the decrease in hematocrit values is the excessive intake of fluid into the body, which leads to a “dilution” of blood, a change in the percentage of red blood cells and plasma. The cause of hyperhydration may be water intoxication with circulatory insufficiency, impaired kidney function. Another reason for the decrease in hematocrit values is hyperproteinemia or an increase in the level of proteins in the blood. With such changes, binding and retention of water in the body occurs. Hyperproteinemia develops in various conditions – vomiting, diarrhea, acute infections, myeloma, Hodgkin’s lymphoma, paraproteinemic hemoblastosis.
Treatment of abnormalities
Hematocrit tes is performed routinely as part of a general blood test. The test is an economical way to diagnose and monitor hematological disorders (anemia, polycythemia), dehydration conditions. If the final indicator deviates from the norm, then it is necessary to consult a general practitioner, pediatrician, hematologist to determine the cause of violations and prescribe treatment. It is possible to prevent the influence of physiological factors on the hematocrit index if you follow the rules of preparation for the blood donation procedure – to give up smoking, heavy physical exertion.