The total blood volume study is a nuclear laboratory test performed to determine the amount of circulating blood volume in the body. It includes a combination of tests for plasma volume and RBC volume that make up the total volume, although the tests can be performed individually, depending on the reason for the study and the needed diagnostic information. The total blood volume is estimated in milliliters (mL) per kilogram (kg) because of the variations in individual body weight and frame. Normally, the blood constitutes 6 to 8 percent of the total body weight. It consists of blood cells suspended in plasma. Plasma forms 45 to 60 percent of the total blood volume and the RBCs constitute most of the remaining volume.⁶⁶

The test involves the IV administration of the client's own RBCs labeled with chromated Cr 51 sodium for RBC volume or human serum albumin labeled with 125I for plasma volume. After the preparation and reinjection of the radiopharmaceutical, blood samples are periodically drawn and the volumes calculated. RBC volume is calculated using the following formula: counting standard expressed as counts per minute per milliliter × 1000 × 5, #db counts per minute per milliliter in the blood sample. Plasma volume is calculated using the following formula: counting standard expressed as counts per minute × 1000, #db counts per minute in the blood sample. When findings in RBC volume exceed 36 mL/kg in male clients and 32 mL/kg in female clients, polycythemia vera is diagnosed, whereas a normal or reduced RBC volume indicates stress polycythemia. Normal or mild changes in plasma volume indicate polycythemia vera, and a reduced plasma volume indicates stress polycythemia.⁶⁷

• IV administration of fluid or blood replacement before the study
• Dehydration, overhydration, or excessive blood loss

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Indications

• Evaluating blood and fluid losses resulting from hemorrhage, burns, surgery, or dehydration:
  • Responses include hypotension, increased pulse, oliguria, or dry skin, leading to shock state or fluid imbalance.
  • A sudden reduction in the total blood volume can lead to shock, whereas a gradual loss can lead to an increasing plasma volume and decreasing RBC volume.
• Differentiating between stress polycythemia and polycythemia vera:
  • RBC volume remains at a normal or reduced level in stress polycythemia and increases in polycythemia vera.
  • Increased RBC volume in combination with increased WBCs and platelets that occur in polycythemia lead to stroke, hemorrhage, myocardial infarction, and venous thrombosis as the blood becomes more viscous.⁶⁸
  • Plasma volume is reduced and hematocrit is elevated with a normal level of RBC volume in stress polycythemia, and it remains at a normal or slightly increased or decreased level in polycythemia vera.
• Determining replacement therapy:
  • In hemorrhage or loss caused by surgery, gastrointestinal bleeding, or trauma, whole blood is usually administered.
  • In reduced RBC volume caused by bleeding or cell destruction, packed RBC is administered.
  • In reduced plasma volume caused by bleeding, burns, or trauma, plasma volume expander is administered.
  • In dehydration state, IV fluids of normal saline or distilled water with or without glucose are administered.
  • This test is used before surgical procedures to anticipate need for replacement therapy and type of replacement needed.
• Monitoring response to replacement therapy

Contraindications

• Pregnancy, unless the benefits of performing the test greatly outweigh the risks to the fetus

[Section Outline]

• Indications
• Contraindications

Nursing Care Before the Procedure

Client preparation is the same as for any study involving the collection of a peripheral blood sample (see Appendix I).

• Inform the client of the injection of a radiopharmaceutical and explain that a minute amount of the material is administered and excreted from the body within 24 hours without causing any harmful effects.
• Inform the client of the schedule for blood samples and explain that the venipunctures are the only discomfort experienced.
• Obtain and record client's height and weight, because values are calculated and expressed in milliliters per kilogram.
• History should include hematologic system information, assessment of vital signs, and potential causes of fluctuations.

Red Blood Cell Volume. The client is placed on the examining table in a supine position for 30 minutes. The prepared dose (5 mL) of the labeled radiopharmaceutical is injected into the vein of one arm. Blood samples (5 mL) are drawn from a vein in the opposite arm in 10 and 40 minutes after the injection. Normally, these samples are equal in counts, but if there is a delay in equal readings caused by splenomegaly or polycythemia, the reading at 40 minutes is more accurate. A 2-mL sample is taken from the 5-mL sample and counted. A microhematocrit is performed to assist in a polycythemia diagnosis. The blood samples are counted to determine the concentration of the radionuclide and compared with the amount administered to obtain the volume of RBCs.

Plasma Volume. The client is placed on the examining table in a supine position for 30 minutes. A blood sample (5 mL) is drawn and centrifuged, and 2 mL is removed to perform a count and establish a standard. The radiopharmaceutical is injected into one arm, and in 10 minutes a blood sample is drawn from the opposite arm. The sample is centrifuged, and 2 mL of plasma is removed and counted. Plasma volume is determined by comparing the counts from the sample with the established count standard.

Nursing Care After the Procedure

Care and assessment after the test are the same as for any study involving a venipuncture for injection or collection of a peripheral blood sample (see Appendix I).

• Assess vital signs and compare them with pretest readings. Continue to monitor if total blood volume falls below 80 mL/kg.
• Monitor ordered replacement therapy such as blood or blood component transfusion or IV fluids.
• Monitor intake and output to prevent or assist in controlling blood or fluid loss or overload, or both.
• Provide support when diagnostic findings are revealed, especially if continuing treatment is necessary, as in polycythemia vera (phlebotomy every 2 to 3 months, myelosuppressive drug therapy to reduce bone marrow activity).