Noble Institute
Pharmacy Department
Practical Human Physiology& Anatomy
First Stage
Hematocrit
Prepared by
Mohammed Kamal
Supervised by
Dr. Rabar Mohammed
1. Introduction to Hematocrit: Definition, Importance, and
Measurement Techniques.
1.1. Definition:
Hematocrit, often abbreviated as HCT or Ht, refers to the volume percentage of red
blood cells in whole blood. It represents the ratio of the volume of red blood cells to
the total volume of blood, including plasma. It's expressed as a percentage or as a
fraction.
1.2. Importance:
1. Oxygen Transport: Red blood cells are responsible for transporting oxygen
from the lungs to tissues throughout the body. A normal hematocrit level
ensures adequate oxygen delivery to tissues, supporting overall metabolic
functions.
2. Diagnosis of Anemia and Polycythemia: Hematocrit levels are pivotal in
diagnosing conditions such as anemia (low hematocrit) and polycythemia
(high hematocrit), which can have significant implications for overall health.
3. Monitoring Health Conditions: Hematocrit levels are monitored in various
medical conditions, including kidney disease, heart disease, and chronic lung
disorders, to assess disease severity and treatment efficacy.
4. Surgical and Transfusion Considerations: Hematocrit levels help determine
the need for blood transfusions during surgeries and assist in evaluating the
response to transfusion therapy.
5. Assessing Hydration Status: In conjunction with other parameters, hematocrit
levels can indicate dehydration or fluid overload, aiding in the management
of fluid balance.
1.3. Measurement Techniques:
1. Centrifugation: The most common method involves centrifuging a blood
sample in a calibrated tube. The denser red blood cells settle at the bottom,
while the less dense plasma rises to the top. The hematocrit level is then
determined by measuring the height of the red blood cell column relative to
the total blood volume.
2. Automated Hematology Analyzers: Modern hematology analyzers automate
the measurement of hematocrit along with other blood parameters. These
machines use various techniques such as impedance, flow cytometry, or
optical methods to quantify the hematocrit level accurately.
3. Microhematocrit Method: In this technique, a capillary tube filled with blood
is sealed at one end and centrifuged to separate the components. The
hematocrit is then determined by measuring the length of the red blood cell
column relative to the total length of the column.
2. Physiological Significance of Hematocrit in Blood
Oxygenation and Transport.
2.1. Oxygen Carrying Capacity:
1. Hematocrit directly affects the oxygen-carrying capacity of blood. Since red
blood cells (RBCs) contain hemoglobin, the protein responsible for binding
and transporting oxygen, a higher hematocrit indicates a greater number of
RBCs available for oxygen transport.
2. An increase in hematocrit (polycythemia) results in enhanced oxygencarrying capacity, potentially beneficial in situations where there's a need for
increased oxygen delivery, such as at high altitudes or during strenuous
physical activity.
3. Conversely, a decrease in hematocrit (anemia) diminishes the blood's oxygencarrying capacity, leading to reduced oxygen delivery to tissues, which can
result in symptoms like fatigue, weakness, and shortness of breath.
2.2.
Tissue Oxygenation:
1. Hematocrit plays a crucial role in ensuring adequate oxygenation of tissues.
As blood circulates through the body, oxygen diffuses from hemoglobin in
RBCs into surrounding tissues, supporting cellular metabolism and energy
production.
2. Higher hematocrit levels facilitate efficient oxygen delivery to tissues,
ensuring optimal cellular function and tissue viability.
3. Lower hematocrit levels can compromise tissue oxygenation, leading to tissue
hypoxia, which can have deleterious effects on organ function and overall
health.
2.3. Oxygen Dissociation Curve
1. Hematocrit influences the shape and position of the oxygen dissociation
curve, which illustrates the relationship between the partial pressure of oxygen
(PO2) and the saturation of hemoglobin with oxygen (SaO2).
2. Changes in hematocrit can alter the affinity of hemoglobin for oxygen,
affecting the ease with which hemoglobin binds to and releases oxygen in
response to changes in tissue oxygen demand.
3. For example, a higher hematocrit shifts the oxygen dissociation curve to the
left, indicating increased hemoglobin affinity for oxygen, whereas a lower
hematocrit shifts the curve to the right, indicating decreased affinity.
2.4. Regulation of Hematocrit
1. The body tightly regulates hematocrit levels to maintain optimal oxygen
transport capacity. Hormonal signals, primarily erythropoietin (EPO) released
by the kidneys in response to low tissue oxygenation, stimulate red blood cell
production in the bone marrow.
2. This regulatory mechanism ensures that hematocrit levels adjust appropriately
to changes in oxygen demand, such as during periods of hypoxia or increased
metabolic activity.
3. Understanding Normal Hematocrit Levels and Variations Based
on Age and Sex
Hematocrit, the proportion of red blood cells (RBCs) in the blood, serves as a vital
parameter in assessing overall health and oxygen-carrying capacity. Normal
hematocrit levels vary based on factors such as age and sex, reflecting the
physiological differences and developmental stages across populations.
3.1. Normal Hematocrit Levels:
1. In adults, the typical range for hematocrit levels is approximately 38% to 52%
for males and 35% to 47% for females.
2. Newborn infants typically have higher hematocrit levels, ranging from 45%
to 60%, which gradually decline over the first few months of life.
3. Children and adolescents may exhibit variations in hematocrit levels as they
grow, with levels generally lower than those of adults until puberty.
4. During pregnancy, maternal hematocrit levels may decrease due to
hemodilution caused by increased plasma volume, resulting in a lower
hematocrit range compared to non-pregnant females.
5.
3.2. Variations Based on Age and Sex:
Neonates and Infants:
Newborns often have higher hematocrit levels compared to adults, reflecting their
higher RBC mass at birth.
Hematocrit levels gradually decrease during the first few months of life as RBC
production slows and plasma volume expands.
Premature infants may have lower hematocrit levels due to reduced RBC production
and increased erythrocyte turnover.
Children and Adolescents:
Hematocrit levels in children and adolescents tend to be lower than those in adults,
primarily due to their smaller RBC mass relative to total blood volume.
Hematocrit levels gradually increase with age, reaching adult levels by late
adolescence or early adulthood.
Pubescent females may experience temporary fluctuations in hematocrit levels due
to menstrual blood loss and hormonal changes.
Adults:
Adult males typically have higher hematocrit levels compared to females, attributed
to androgen-mediated stimulation of erythropoiesis.
Hematocrit levels in females are influenced by menstrual cycles, pregnancy, and
hormonal fluctuations, leading to variations within the normal range.
Elderly Population:
Hematocrit levels may decrease with advancing age due to age-related decline in
erythropoiesis and changes in bone marrow composition.
Age-related comorbidities and medication use can also impact hematocrit levels in
the elderly population.
4. Impact of Altitude, Chronic Diseases, and Medications on
Hematocrit Levels.
The impact of altitude, chronic diseases, and medications on hematocrit levels can
significantly influence blood oxygenation, overall health, and the interpretation of
hematological parameters. Here's an overview of how each factor affects hematocrit:
4.1. Altitude:
High Altitude
- At higher altitudes, the partial pressure of oxygen (PO2) in the atmosphere
decreases, resulting in decreased oxygen availability.
- To compensate for reduced oxygen levels, the body initiates adaptive responses,
including increased production of erythropoietin (EPO) by the kidneys.
- Elevated EPO levels stimulate bone marrow to produce more red blood cells,
leading to an increase in hematocrit levels over time.
- This adaptive response, known as altitude acclimatization, helps enhance oxygencarrying capacity and improve tissue oxygenation at high altitudes.
4.2. Chronic Diseases:
- Chronic Kidney Disease (CKD):
- In CKD, impaired kidney function leads to decreased production of erythropoietin
(EPO), which stimulates red blood cell production.
- Consequently, patients with CKD often develop anemia due to reduced
erythropoiesis, resulting in lower hematocrit levels.
- Anemia in CKD may also be exacerbated by other factors such as inflammation,
iron deficiency, and blood loss.
- Chronic Respiratory Diseases (e.g., COPD): - Chronic respiratory diseases, such
as chronic obstructive pulmonary disease (COPD), can impact hematocrit levels
through mechanisms such as chronic hypoxemia and polycythemia.
- Chronic hypoxemia stimulates the production of erythropoietin, leading to
increased red blood cell production and elevated hematocrit levels (secondary
polycythemia) as a compensatory mechanism to improve oxygen-carrying capacity.
- However, in advanced stages of COPD, patients may experience chronic
respiratory failure and subsequent hypoxemia, which can lead to a decrease in
hematocrit levels due to impaired erythropoiesis.
4.3. Medications:
- Erythropoiesis-Stimulating Agents (ESAs):
- ESAs, such as recombinant human erythropoietin (epoetin alfa, darbepoetin alfa),
are synthetic forms of erythropoietin used to stimulate red blood cell production in
conditions associated with anemia.
- Administration of ESAs can lead to an increase in hematocrit levels by stimulating
bone marrow erythropoiesis and promoting the maturation of red blood cells.
- However, ESA therapy must be carefully monitored to avoid excessive increases
in hematocrit levels, which can increase the risk of adverse cardiovascular events
such as thrombosis and hypertension.
- Diuretics:
- Diuretics, commonly used to treat conditions such as hypertension and heart
failure, can lead to dehydration and hemoconcentration, resulting in an increase in
hematocrit levels.
- By promoting fluid loss, diuretics can cause a relative increase in the proportion
of red blood cells within the blood volume, leading to higher hematocrit values.
Conclusion
In conclusion, understanding normal hematocrit levels and variations based on age
and sex is crucial for accurate interpretation of hematological parameters and clinical
assessment of overall health and well-being across different populations.
Understanding the impact of altitude, chronic diseases, and medications on
hematocrit levels is essential for accurate interpretation of hematological parameters
and appropriate management of patients with various health conditions. Monitoring
hematocrit levels in clinical practice can help assess oxygen-carrying capacity,
identify underlying pathologies, and guide therapeutic interventions as needed.