FAQ ON HEMATOCRIT (HCT) AND ITS CLINICAL SIGNIFICANCE
WHAT IS HAEMATOCRIT (HCT), AND WHY IS IT IMPORTANT IN A FULL BLOOD COUNT (FBC)?
Haematocrit (HCT) is a measure of the proportion of your blood that is made up of red blood cells. It is expressed as a percentage, indicating how much of your blood's volume is occupied by red blood cells. For example, a haematocrit of 45% means that 45% of the volume of blood is made up of red blood cells. Haematocrit is an important parameter in a Full Blood Count (FBC) because it provides information about your blood's ability to carry oxygen. Red blood cells contain haemoglobin, the protein responsible for oxygen transport, so the haematocrit level can give doctors insights into whether your body is getting enough oxygen or if there are any underlying conditions affecting your blood.
WHAT IS THE NORMAL RANGE FOR HAEMATOCRIT IN AN FBC?
The normal range for haematocrit varies depending on age, gender, and individual health factors. For adult men, the typical range is between 40% and 52%, while for adult women, it is generally between 36% and 48%. These ranges may differ slightly depending on the laboratory's reference values. It's also important to consider that factors like pregnancy, living at high altitudes, or dehydration can influence haematocrit levels. During pregnancy, haematocrit levels might decrease due to the increased plasma volume, while living at high altitudes may result in higher haematocrit levels as the body adapts to lower oxygen levels in the environment.
WHAT DOES A LOW HAEMATOCRIT LEVEL INDICATE?
A low haematocrit level, known as anaemia, indicates that there are fewer red blood cells in the blood than normal, which means the body might not be getting enough oxygen. Anaemia can have various causes. One common cause is a deficiency in essential nutrients like iron, vitamin B12, or folate, all of which are necessary for red blood cell production. Iron-deficiency anaemia is the most prevalent form of anaemia and occurs when the body doesn't have enough iron to produce sufficient haemoglobin.
Chronic diseases, such as kidney disease or chronic inflammation, can also lead to low haematocrit levels. The kidneys produce erythropoietin, a hormone that stimulates the bone marrow to produce red blood cells. When kidney function is impaired, erythropoietin production may decrease, leading to lower haematocrit levels. Additionally, significant blood loss from surgery, injury, or internal bleeding can reduce haematocrit. Inherited conditions like thalassaemia or sickle cell disease can also result in anaemia by affecting the production or lifespan of red blood cells. Symptoms of low haematocrit often include fatigue, weakness, pale skin, shortness of breath, and dizziness, all due to the reduced oxygen-carrying capacity of the blood.
WHAT DOES A HIGH HAEMATOCRIT LEVEL INDICATE?
A high haematocrit level, known as polycythaemia, indicates that there are more red blood cells in the blood than normal. This can make the blood thicker and increase the risk of blood clots, which can lead to complications such as stroke or heart attack. One common cause of high haematocrit is dehydration. When the body loses fluids, the volume of plasma in the blood decreases, making the red blood cells more concentrated and increasing the haematocrit level.
Living at high altitudes can also lead to a higher haematocrit level because the body produces more red blood cells to compensate for the lower oxygen levels in the environment. This adaptation helps deliver sufficient oxygen to tissues despite the thinner air. However, certain medical conditions can also cause polycythaemia. For example, polycythaemia vera is a type of blood cancer where the bone marrow produces too many red blood cells, leading to elevated haematocrit. Chronic lung diseases and heart conditions that reduce oxygen levels in the blood can also trigger an increase in haematocrit as the body attempts to improve oxygen delivery by producing more red blood cells.
HOW DOES HAEMATOCRIT RELATE TO OTHER FBC PARAMETERS?
Haematocrit is closely related to other parameters in the Full Blood Count (FBC), such as haemoglobin levels, red blood cell (RBC) count, and red cell indices like mean corpuscular volume (MCV) and mean corpuscular haemoglobin (MCH). Haemoglobin is the protein in red blood cells that carries oxygen, so its levels are usually correlated with haematocrit. If your haematocrit is low, your haemoglobin levels are likely also low, suggesting anaemia.
The RBC count measures the number of red blood cells in your blood. Haematocrit is essentially a reflection of this count, showing the volume percentage that these cells occupy. Therefore, changes in RBC count are often mirrored by changes in haematocrit. For example, a low RBC count will usually result in a low haematocrit, indicating anaemia.
Red cell indices, including MCV and MCH, provide further details about the characteristics of your red blood cells. MCV measures the average size of your red blood cells, while MCH indicates the average amount of haemoglobin in each red blood cell. These indices help doctors understand the type and cause of anaemia. For example, microcytic anaemia, often due to iron deficiency, is characterised by a low MCV. Meanwhile, macrocytic anaemia, which can be caused by vitamin B12 or folate deficiency, shows a high MCV. The relationship between haematocrit and these other parameters helps doctors diagnose and monitor conditions affecting red blood cells and overall blood health.
WHAT IS THE SIGNIFICANCE OF HAEMATOCRIT LEVELS IN CLINICAL PRACTICE?
Haematocrit levels are a key indicator of overall blood health and are used in clinical practice to diagnose and monitor a variety of conditions. Low haematocrit levels are a common sign of anaemia, prompting further investigation to determine the underlying cause. Depending on the cause, treatment may involve dietary changes, supplements, or managing underlying conditions like kidney disease or chronic blood loss.
High haematocrit levels, on the other hand, can indicate polycythaemia, which may require treatment to reduce the risk of complications like blood clots. This might involve therapeutic phlebotomy (removal of blood from the body) or medications to decrease red blood cell production. In some cases, treating the underlying condition, such as improving oxygenation in lung disease, can help normalise haematocrit levels.
Monitoring haematocrit levels is also crucial in managing chronic conditions that affect red blood cell production or oxygen transport. For example, in patients with chronic kidney disease or heart failure, regular monitoring of haematocrit can help doctors adjust treatment plans to ensure the body is receiving enough oxygen.
CAN HAEMATOCRIT LEVELS FLUCTUATE, AND WHAT FACTORS INFLUENCE THESE FLUCTUATIONS?
Yes, haematocrit levels can fluctuate due to various factors. Dehydration can cause a temporary increase in haematocrit by reducing plasma volume, making the blood more concentrated. Conversely, overhydration can dilute the blood, leading to a lower haematocrit level. Physical activity, particularly endurance exercise, can also influence haematocrit levels, as the body adapts to increased oxygen demand.
Living at high altitudes is another factor that can raise haematocrit levels, as the body compensates for lower oxygen levels by producing more red blood cells. Smoking can also increase haematocrit levels, as the body responds to reduced oxygen levels caused by carbon monoxide exposure by producing more red blood cells. Certain medications, such as erythropoiesis-stimulating agents used in chronic kidney disease, can also elevate haematocrit by stimulating red blood cell production.
