Hematocrit

Understanding hematocrit is essential for assessing blood health and diagnosing various medical conditions. Hematocrit, often abbreviated as Hct, is a key component of a complete blood count (CBC) test, providing valuable insights into the composition and quality of blood.

Hematocrit refers to the proportion of red blood cells (erythrocytes) in the total volume of blood. It is typically expressed as a percentage and represents the volume of red blood cells relative to the total blood volume.

Hematocrit plays a crucial role in oxygen transport throughout the body. By carrying oxygen-rich red blood cells, hematocrit ensures that vital organs and tissues receive the oxygen they need to function optimally. Additionally, hematocrit levels are indicative of blood viscosity and hydration status, offering insights into overall blood health.

Hematocrit is an essential biomarker in assessing the fundamental health status of an individual.  

Definition and Function of Hematocrit

What is Hematocrit?  [2., 6.]

Hematocrit (HCT), derived from "hemato-" and Greek "krites," measures the proportion of packed red blood cells (RBC) in whole blood, also termed packed cell volume (PCV). It's commonly used to diagnose anemia or polycythemia and to monitor treatment response.

Typically determined via centrifugation, it separates blood into layers, with RBCs at the bottom and plasma at the top. While traditionally measured using a Wintrobe tube or capillary tube, automated analyzers are now more prevalent. 

Hematocrit levels indicate conditions like anemia or erythrocytosis and may guide transfusion decisions, with changes over time reflecting treatment response. However, factors like plasma trapping, hyperglycemia, or pregnancy can influence results.

What is the Significance of Hematocrit?

Hematocrit is a foundational marker of blood health; it can signify an excess or deficiency of red blood cells.  Changes in the hematocrit may occur as part of a physiological process, as in pregnancy, or as part of a pathologic process, as in anemia or some chronic diseases.  

High Hematocrit (Polycythemia): Elevated hematocrit levels may indicate polycythemia, a condition characterized by an excess of red blood cells. This could result from factors like dehydration, chronic hypoxia, smoking, or underlying diseases like polycythemia vera. 

Clinically, high hematocrit can increase blood viscosity, leading to complications such as thrombosis, stroke, or heart attack.

Low Hematocrit (Anemia): Conversely, low hematocrit levels may indicate anemia, which signifies a reduced number of red blood cells or decreased hemoglobin levels. 

Anemia can result from various causes, including nutritional deficiencies (such as iron, vitamin B12, or folate deficiency), chronic diseases (like chronic kidney disease or inflammatory conditions), or blood loss (either acute or chronic). 

Clinically, anemia can lead to symptoms such as fatigue, weakness, shortness of breath, and impaired exercise tolerance.

Hematocrit Changes in Pregnancy: During pregnancy, hematocrit levels typically decrease due to expansion of plasma volume, which is a physiological adaptation to support the growing fetus and maintain adequate circulation. 

This dilutional effect can result in lower hematocrit values, commonly observed in the second and third trimesters. While mild decreases are normal, significant deviations may indicate conditions like anemia or gestational hypertension, necessitating further evaluation.

Hematocrit Changes in Chronic Disease: In chronic diseases, hematocrit levels may be influenced by various factors. For instance, in chronic kidney disease, reduced erythropoietin production can lead to decreased red blood cell production and subsequently lower hematocrit levels, contributing to anemia. 

Similarly, chronic inflammatory conditions like rheumatoid arthritis or inflammatory bowel disease can trigger immune-mediated mechanisms that disrupt erythropoiesis, resulting in anemia and lower hematocrit levels.  [4., 11.]

Conversely, certain chronic conditions associated with hypoxia, such as chronic obstructive pulmonary disease (COPD), may stimulate erythropoiesis and lead to elevated hematocrit levels as a compensatory response to tissue hypoxia. However, it’s important to note that COPD can manifest either high or low hematocrit.  [9.] 

These hematocrit fluctuations serve as important diagnostic and prognostic indicators in the management of chronic diseases.

Laboratory Testing for Hematocrit

Procedure for the Hematocrit Blood Test

The hematocrit test is typically performed as part of a complete blood count (CBC) analysis. During the procedure, a small sample of blood is drawn from a vein in the arm using a needle. The blood sample is then sent to a laboratory for analysis. 

Preparation for the Hematocrit Blood Test

No special preparation is usually required for the hematocrit test. Patients can typically eat and drink normally before the test and do not need to fast. 

Interpreting Test Results

Reference Range for Hematocrit Tests

It is important to consult with the ordering laboratory company for their reference ranges used.  However, typical reference ranges for hematocrit include:  [5.]

Reference ranges (SI units/conventional units) are as follows:

Males - 0.40-0.54/40-54%

Females - 0.36-0.46/36-46%

Newborns - 0.53-0.69/53-69%

Clinical Significance of High Hematocrit: What Does High Hematocrit Mean?

Elevated hematocrit levels indicate an increase in the concentration of red blood cells.  Elevations in hematocrit are associated with polycythemia, which is characterized as absolute or relative.

Polycythemia is a condition characterized by an elevated level of red blood cells (erythrocytes) in the bloodstream, which can be caused by various factors such as increased production of red blood cells, decreased plasma volume, or other underlying medical conditions.  

Absolute polycythemia refers to an increase in the total mass of red blood cells in the body, leading to higher-than-normal levels of red blood cells in the bloodstream. This can result from factors such as increased production of red blood cells (erythropoiesis) due to conditions like polycythemia vera or secondary polycythemia.

Relative polycythemia, on the other hand, is characterized by an increase in the concentration of red blood cells in the bloodstream due to a decrease in plasma volume, without a corresponding increase in the total mass of red blood cells. This reduction in plasma volume can occur due to dehydration, shock, or certain medications like diuretics.

Causes of elevated hematocrit include: 

Absolute polycythemia:  [8.]

• Hypoxia: low oxygen levels in the blood stimulate the production of red blood cells, leading to increased hemoglobin levels.

• Inappropriate erythropoietin production: abnormal secretion of erythropoietin, a hormone that regulates red blood cell production, results in an excess of red blood cells and elevated hemoglobin.

• Genetic polycythemia: inherited genetic mutations can cause the bone marrow to produce too many red blood cells, resulting in elevated hemoglobin levels.

• Polycythemia vera: a rare blood disorder characterized by the overproduction of red blood cells by the bone marrow, leading to increased hemoglobin levels.

• Smoking: smoking increases carbon monoxide levels in the blood, which binds to hemoglobin more readily than oxygen.  This leads to reduced oxygen-carrying capacity and compensatory increased production of red blood cells, resulting in elevated hemoglobin levels.

Relative polycythemia:  [1.] 

• Dehydration: reduced plasma volume due to dehydration leads to a relative increase in the concentration of red blood cells and hemoglobin in the blood.

• Shock: in conditions of shock, such as hypovolemic shock, there is a decrease in blood volume relative to the number of red blood cells, resulting in elevated hemoglobin levels.

• Diuretic therapy: certain diuretic medications can cause dehydration by increasing urine output, leading to relative polycythemia and elevated hemoglobin levels.

• Spurious polycythemia (Gaisböck syndrome): this condition is characterized by an increase in red blood cell count and hemoglobin levels due to factors such as stress, smoking, and obesity, rather than an actual increase in red blood cell mass.

Clinical Significance of Low Levels of Hematocrit: What Does Low Hematocrit Mean?  [10.]

Low levels of hematocrit signify anemia and hold significant clinical importance due to their impact on overall health and physiological function.  Essentially, low hemoglobin also means that the tissues of your body are not getting enough oxygen.  

Anemia carries significant clinical implications. Anemia can lead to symptoms such as fatigue, weakness, and shortness of breath, impacting daily functioning and quality of life. 

Severe anemia may present with syncope, reduced exercise tolerance, and exacerbation of underlying health conditions, including cardiovascular disease. Additionally, anemia can result in tissue hypoxia, further complicating existing comorbidities and increasing the risk of adverse outcomes, such as heart failure or cognitive impairment. 

Microcytic Anemia (MCV < 80 fl):

• Iron deficiency anemia: typically due to inadequate dietary iron intake or chronic blood loss

• Anemia of chronic disease (AOCD): associated with chronic inflammatory conditions

• Sideroblastic anemia: characterized by defective heme synthesis

• Thalassemia: genetic disorders affecting hemoglobin production

• Lead poisoning: inhibits enzymes involved in heme synthesis

Normocytic Anemia (MCV 80-100 fL):

• Anemia of chronic disease (AOCD): resulting from chronic inflammation

• Renal failure: impaired erythropoietin production

• Aplastic anemia: bone marrow failure

• Pure red cell aplasia: selective suppression of erythropoiesis

• Myelofibrosis or myelophthisic processes: replacement of bone marrow by fibrous tissue

• Multiple myeloma: plasma cell disorder affecting bone marrow function

Macrocytic Anemia (MCV > 100 fL):

• Alcohol: direct toxic effect on bone marrow

• Liver disease: impaired metabolism of folate and vitamin B12

• Hypothyroidism: altered erythrocyte metabolism

• Folate and Vitamin B12 deficiency: essential for DNA synthesis in erythropoiesis

• Myelodysplastic syndrome (MDS): clonal disorders of hematopoietic stem cells

Hemolytic Anemia:

• Extravascular hemolysis: spleen and liver remove damaged red blood cells prematurely

• Hemoglobinopathies, enzymopathies, and membrane defects: genetic disorders affecting red blood cell structure and function

• Drug-induced hemolysis: certain medications can trigger immune-mediated destruction of red blood cells

• Intravascular hemolysis: red blood cells lyse within the circulation

• Paroxysmal nocturnal hemoglobinuria (PNH): deficiency in complement regulatory proteins on red blood cells

• Autoimmune hemolytic anemia (AIHA): immune system attacks its own red blood cells

• Transfusion reactions, microangiopathic hemolytic anemias, disseminated intravascular coagulation (DIC): conditions leading to intravascular hemolysis

Related Biomarkers

The hematocrit test is a standard part of the Complete Blood Count (CBC) test, a routine blood panel.  

Related biomarkers such as hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) are routinely evaluated alongside hematocrit levels. These additional parameters provide valuable insights into the size, volume, and concentration of red blood cells, aiding in the diagnosis and classification of various types of anemia.

Other biomarkers to consider include: 

Serum Iron: measures the concentration of iron in the blood. Low levels may indicate iron deficiency anemia, while high levels could be suggestive of hemochromatosis or iron overload disorders.

Total Iron-Binding Capacity (TIBC): reflects the blood's capacity to bind and transport iron. Elevated TIBC levels are seen in iron deficiency anemia, while decreased levels may indicate iron overload conditions.

Ferritin: reflects the body's iron stores. Low ferritin levels are indicative of iron deficiency anemia, whereas elevated levels may suggest inflammation, liver disease, or iron overload disorders.

Transferrin Saturation (TSAT): represents the percentage of transferrin saturation with iron. Helps assess iron availability for erythropoiesis, with low TSAT levels observed in iron deficiency anemia.

Serum Vitamin B12 and Folate Levels: assess levels of vitamin B12 and folate, essential for erythropoiesis. Deficiencies in these vitamins can lead to macrocytic anemia.

Erythropoietin (EPO) Levels: measure the concentration of erythropoietin, a hormone that stimulates red blood cell production. Elevated levels may indicate anemia due to renal failure or chronic hypoxia.

Peripheral Blood Smear: provides a qualitative assessment of red blood cell morphology, allowing identification of abnormal cell shapes, sizes, and inclusions. Helpful for diagnosing hemolytic anemias and other hematological disorders.

Natural Ways to Support Healthy Hematocrit Levels  [3., 7.]

Maintaining healthy iron levels is an essential component to healthy blood tests.  

• Incorporate iron-rich foods into your diet, such as lean meats, poultry, fish, beans, lentils, tofu, spinach, kale, and fortified cereals.

• Pair iron-rich foods with sources of vitamin C, like citrus fruits, strawberries, bell peppers, and tomatoes, to enhance iron absorption.

• Avoid drinking tea or coffee with meals, as they contain compounds that can inhibit iron absorption.

• Cook in cast-iron pots and pans, as they can increase the iron content of food.

• Consume fermented foods like yogurt, kefir, and sauerkraut, which can improve gut health and enhance iron absorption.

• Limit consumption of calcium-rich foods and supplements during meals, as calcium can interfere with iron absorption.

• Eat foods rich in folate, vitamin B12, and vitamin A, as they play crucial roles in red blood cell production and iron metabolism.

• Consider incorporating iron supplements under the guidance of a healthcare professional if dietary sources alone are insufficient to meet your iron needs.

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