What is a blood volume test?

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.

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.

Reviewed by a Cleveland Clinic medical professional.

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