How much blood do you have in your body? Let's learn about the Blood Volume Test in simple terms (Blood Volume Testing)

We all talk about our blood pressure and blood sugar levels and check them regularly. But have you ever wondered how much blood you have in your body? That is, is that amount of blood just right for your body? Or is it too much? Or is it too little? Today we are going to talk about a special test that seeks to answer that question.

What is this Blood Volume Test?

Simply put, a Blood Volume Test is a test that measures the total amount of blood in your body. This is not like a regular blood test. This belongs to a field called Nuclear Medicine. Don't be scared by the word "nuclear." This involves using a very small, harmless radioactive substance to study how certain processes occur in the body. It's like shining a small torch inside the body.

Let's first look at what our blood is made of.

Before we understand this test, let's briefly remind ourselves what's in our blood. Our blood is not a single substance. It's a collection of several components.

Of these components, white blood cells and platelets make up less than 1% of the blood volume. Therefore, the Blood Volume Test mainly measures the amount of plasma and red blood cells . Therefore, this test is sometimes called ``Plasma Volume Test``.

How does our body control this amount of blood?

Our body is an amazing machine. Inside it, a very complex system operates to keep this blood volume at the right level.

• Red blood cells: New red blood cells are made in the bone marrow inside our bones. Old cells are destroyed and removed by our liver . This process takes a while. If a large amount of blood is lost from an accident, it can take days, or even months, for new red blood cells to be made.
• Plasma: Plasma is mostly water. So it is much faster to control than to make red blood cells. The body gets fluids from the water we drink and the food we eat. Fluid is lost from the body through sweat, urine, and breathing. Our kidneys are the main ones that keep this fluid level in balance.

An average adult has about 5 liters of blood in their body. However, this amount can vary due to various diseases or other reasons.

Increased blood volume (Hypervolemia) and decreased blood volume (Hypovolemia)

There are two main conditions that occur when blood volume exceeds normal levels. Let's look at these two separately.

What is the relationship between blood volume and blood pressure?

This is very easy to understand. Think of a pipe that is being pumped with water by a water motor.

• When blood volume increases (Hypervolemia): It's like putting more water pressure on a pipe. The pressure inside the blood vessels increases. That means blood pressure rises.
• When the blood volume decreases (Hypovolemia): Just like the amount of water in a tube decreases, the pressure inside the blood vessels decreases. That means the blood pressure drops. The body tries to maintain the pressure by causing the blood vessels to contract. But if the blood loss is severe, the body cannot control it.

So when should this test be done?

This is not a routine test for everyone. Doctors recommend this test especially for patients in the Emergency Treatment Unit (ETU) or Intensive Care Unit. It may also be necessary in the following cases:

• In case of severe bleeding
• In case of severe dehydration
• In heart conditions
• In case of kidney or liver diseases
• In severe burn injuries
• For patients in shock
• To find the cause of anemia
• To find the cause of frequent syncope
• If you have uncontrolled high or low blood pressure
• To check the patient's condition before major surgery

Let's learn step by step how to do the test.

This test is usually done in the hospital. It may be done right at your bedside, or you may need to go to the nuclear medicine department.

How do you prepare before the test?

Your doctor will advise you on this. Usually,

• You will be asked to refrain from eating or drinking for a few hours before the test.
• Do not drink beverages containing caffeine, such as coffee or tea, on the day of the test. Caffeine is a diuretic.
• If you are taking any medications, be sure to ask your doctor if you need to stop them before the test.

What happens during the test?

This process is very simple. There is nothing to worry about.

1. First, a technician will measure your height and weight.

2. Then a cannula (IV line) will be inserted into a vein in your arm.

3. You should be lying comfortably in bed.

4. Next, a very small amount of the radioactive substance I mentioned earlier (`Iodine-131 human serum albumin (HSA)`) is injected into the body through the cannula.

5. Wait about 12 minutes for this substance to mix well with your blood.

6. After that, several blood samples are taken about every 6 minutes and sent to the laboratory.

7. The entire process usually takes no more than 90 minutes.

What do you do after the test?

When the test is finished, the cannula will be removed. You can go home. Some of the radioactive material that was put into your body will be excreted in your urine, while the rest will naturally break down and disappear in your body. It is very important to drink plenty of water to speed up this process.

Are there any risks with this test?

As with any medical test, there are a few things to keep in mind.

• If you are pregnant or breastfeeding: This test is not recommended if you are pregnant or breastfeeding. Therefore, you can take a pregnancy test before the test to confirm whether you are pregnant.
• Allergies: If you have any allergies to iodine, shellfish, or eggs , be sure to tell your doctor. If so, your doctor may be able to modify the test to avoid causing an allergic reaction.
• Effects on the thyroid gland: The radioactive iodine used in the test can damage your thyroid gland. To prevent this, you will be given an iodine tablet to drink before the test. Then, your thyroid gland absorbs the iodine, blocking the absorption of the radioactive iodine.

What do the results say?

The test report clearly shows whether your blood volume is normal, low, or high.

This information is very important to your doctor. It can be a big clue to help you find the cause of your illness. For example:

• If you have low blood volume (hypovolemia) , you may be given fluids such as saline or, if necessary, blood transfusions.
• If you have high blood volume (hypervolemia) , you may be given medication to help you eliminate excess fluid from your body through urine.

In this way, the results of this test are of great help to doctors in accurately determining what treatment to give the patient and in what dosage.

Blood Volume, Blood Volume Test, Blood Tests, Hypervolemia, Hypovolemia, Blood Pressure, Dehydration, Kidney Disease, Heart Attack