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What is a Blood Volume Test? Procedure & Risks

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A blood volume test (also called a plasma volume test or a red cell mass test) is a nuclear lab procedure used to measure the volume (amount) of blood in the body. The test also measures the volume of plasma and of red cells in the blood.

blood volume test 

What is syncope?

Syncope (pronounced "sin ko pea") is the brief loss of consciousness and posture caused by a temporary decrease in blood flow to the brain. Syncope may be associated with a sudden fall in blood pressure, a decrease in heart rate or changes in blood volume or distribution. The person usually regains consciousness and becomes alert right away, but may experience a brief period of confusion.

Syncope is often the result of an underlying medical condition that could be related to your heart, nervous system or blood flow to the brain.

A blood volume test can be used in the diagnosis of these conditions:

  • Hypovolemia (low blood volume)
  • Hypervolemia (high blood volume)
  • Anemia (low red cell volume)
  • Polycythemia (high red cell volume)

A blood volume test also helps in the evaluation and treatment of these conditions:

  • Orthostatic hypotension (low blood pressure while upright)
  • Hypertension (high blood pressure)
  • Heart failure (decreased pumping power of the heart)
  • Shock
  • Medical conditions associated with acute blood loss

A blood volume test may be used in the evaluation of these treatments:

  • Kidney dialysis
  • Pre-operative hemodilution (blood dilution) therapy
  • Pre- and post-evaluation of fluid status
  • Pseudo-anemia detection secondary to fluid retention
  • Blood transfusion therapy/precise volume replacement

The blood volume test results help your doctor determine the cause of symptoms, abnormal laboratory results or certain circulation disorders. The test results also will help your doctor plan a course of treatment.

What are the risks of the test?

As with any procedure, there are risks of the blood volume test. Your healthcare provider will discuss the risks and benefits of the procedure with you before the test is ordered.

If necessary, the test will be modified to minimize any potential risks.

The main risk of the procedure is an allergic reaction to the iodine used in the test, although this is rare. If needed, Benadryl can be given in the lab.

Bruising or swelling at the IV site are common reactions, as well as pain or discomfort when the IV is inserted. Please talk to the lab staff if you are concerned about the IV insertion.

This information is about testing and procedures and may include instructions specific to Cleveland Clinic. Please consult your physician for information pertaining to your testing.

Scheduling this test

The scheduling secretary will tell you when to report for your blood volume test after your appointment with your primary care provider or after the tilt table test has been completed. If you are scheduling this test by phone, your appointment schedule will be mailed to you.

How long will the test last?

The test takes about one hour to complete. Please plan on being at the hospital for one to 1 ½ hours for your appointment.

Should I take my medications?

Yes. You may take your prescription medications as you normally would, with water. However, do not take diuretics or laxatives before the test.

If you have diabetes, please request a mid-morning appointment so you may eat a light breakfast at least four hours prior to testing, and also complete the test in time for lunch.

If you have questions or need help making adjustments to your medications, please call your physician. Do not discontinue any medication without first talking to your healthcare provider.

Can I eat before the test?

Eat a normal meal the evening before your procedure. DO NOT eat or drink anything except water for four hours before the test.

On the day of the procedure, do not eat or drink anything containing caffeine. This includes caffeine-free and decaffeinated products since they may contain small amounts of caffeine. Ask your doctor or pharmacist if any of your medications (prescription or over-the-counter) contain caffeine so that you can make adjustments in your medication schedule the day of the test, if necessary.

What should I wear?

Wear comfortable clothes. You may wear a short-sleeved or sleeveless t-shirt in place of a hospital gown. If you are wearing a long-sleeved or tight-fitting shirt, you may be asked to remove it and change into a hospital gown for the test. You will be given a locker for your clothing.

Please leave all jewelry (including wedding rings), watches and valuables at home.

What should I bring?

Please bring the following to your appointment:

  • Recent medical history and physical exam report
  • Medical records pertinent to your health condition (if available)
  • List of current medications and dosages
  • List of allergies (including medication, food and environmental allergies)
  • Your insurance card

Where do I go for my appointment?

The appointment secretary will tell you where to check in for your appointment. Please check in about 10 minutes before your scheduled appointment time.

Before going to the testing area, your height and weight will be recorded.

You will have an opportunity to use the restroom before the test.

Where is the test performed?

The test is performed in the Syncope Lab.

What happens before the test?

A nurse will explain the procedure in detail and answer any questions you may have.

A pregnancy test may be ordered before the test if necessary, as this test may be unsafe to the baby if you are pregnant. This test is also not performed if you are breastfeeding.

This information is about testing and procedures and may include instructions specific to Cleveland Clinic. Please consult your physician for information pertaining to your testing.

IV Placement:

An IV (intravenous) line will be placed in a vein in your arm. The IV is used to take blood samples for blood tests ordered by your doctor, and to inject the radioactive isotope and tagging agent. If necessary, medications are delivered through the IV during the test.

Blood Volume Analysis, Blood Tests:

During the blood volume analysis portion of the test, a small amount of a radioactive isotope, or tracer called iodinated-RISA, is injected. If you are allergic to iodine, IVP dye, shellfish or eggs, the test will be modified to minimize any potential risk of an allergic reaction. Blood samples are then taken and analyzed. The blood volume test is used to evaluate if the amount of blood in your body is appropriate for your gender, height and weight.

A hematocrit measurement is also taken. This blood test calculates the percentage of red blood cells in the bloodstream. A low hematocrit reading may indicate the presence of anemia.

Other blood samples may be ordered to determine the level of certain blood pressure-regulating hormones produced by your kidneys and adrenal glands or to test for electrolytes in the blood, such as sodium and potassium.

Will I be awake during the test?

Yes. You will be awake during the test. You will lie on your back on an exam table for the entire test. Minimal movement is allowed during the test, except for sitting up, to allow accurate recording of the test results. We will try to make you as comfortable as possible during the test.

How will I feel during the test?

Throughout the test, the nurse or technician will ask you how you feel. You may not have any symptoms, or you may experience pre-syncope symptoms (called premonitory symptoms), such as light-headedness, nausea and palpitations (fluttering in the chest).

It is important to tell the staff how you are feeling throughout the test. Adjustments can be made between sets of images if necessary to make you more comfortable.

This information is about testing and procedures and may include instructions specific to Cleveland Clinic. Please consult your physician for information pertaining to your testing.

What happens after the test?

The IV will be removed after your last test of the day. Bruising or swelling at the IV site are common reactions, but talk to the lab staff if you are concerned.

Some of the tracer that was injected is eliminated through urination, and the rest breaks down naturally. You may drink extra fluids to help eliminate the isotope more quickly, although this is not necessary.

You will receive a Homeland Security card that you should carry with you for three months after the test.

Going home after the test

You are usually able to go home after the test. If symptoms are severe, a responsible adult should drive you home after the test.

When will I get the test results?

A full report with the blood volume test results will be sent to your referring or primary care physician in three to five business days. You will also receive a copy of the letter in seven to 10 days.

Your referring physician or primary care physician will discuss the test results with you and discuss any necessary changes in your treatment.

Your medications may be changed or you may start to take new medications. You may be referred to other doctors or services to treat your condition.

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