An RBC survival time study is a nuclear laboratory test performed to determine whether an anemic state is caused by a decrease in the survival of RBCs. Normally, RBCs have a life span of 120 days, with 0.8 percent loss per day and a half-time of 60 days. The normal half-time, which serves as a basis for determining the rate of survival or destruction in this study, is 25 to 35 days for this test because of an additional loss of tagging from RBCs.⁶⁹ When the RBCs are destroyed or sequestered in the spleen, the life span of the cells is reduced and a diagnosis of hemolysis can be made as a cause of anemia. The study is performed in combination with RBC volume and iron studies (see Chapter 1 - Hematology and Tests of Hematopoietic Function).

The test involves two stages. The first stage provides laboratory testing of blood after the injection of a specially prepared radiopharmaceutical. The client's own blood is drawn and labeled with chromated Cr 51 sodium and reinjected. Scheduled blood samples are drawn daily to test for blood levels of radioactivity in the circulation. The second stage provides for a scanning of the spleen to determine whether the reduced life span of the RBCs is caused by splenic sequestration. The liver and pericardium are also scanned to determine pathogenic mechanisms. Counts are made for each area and a ratio is established for spleen to liver and spleen to pericardium to determine splenic abnormalities, because a rising ratio indicates sequestration significant to RBC destruction.

[Show Table Outline]

Survival Time

Normal life span of RBCs = 120 days, with a normal loss of 0.8% per day

Normal half-time of RBCs = 60 days

Normal half-time of labeled RBCs = 25-35 days

Splenic Sequestration

Spleen-to-liver ratio = 1:1

Spleen-to-pericardium ratio = 2:1 or less

[Table Outline]

• Survival Time
• Splenic Sequestration

• Recent transfusion or hemorrhage falsely decreases RBC survival.
• High WBC and platelet counts falsely decrease RBC survival time.

[Show Section Outline]

Indications

• Known or suspected hemolytic anemia conditions causing a decreased survival value:
  • Intrinsic or extrinsic defects listed in Table 20-2
  • Identification of the need for further studies to confirm diagnosis of intrinsic or extrinsic defects causing the anemia
• Known or suspected disorders causing an increased survival of RBCs as revealed by more than a 35-day survival value:
  • Erythrocytosis caused by primary or secondary polycythemia or thalassemia minor
  • Chronic hypoxia, respiratory or cardiovascular disease, high altitudes, hypoventilation syndromes, and renal disorders, which can stimulate production of RBCs
• Determination of RBC sequestration in the spleen as revealed by a spleen-to-liver or spleen-to-pericardium ratio:
  • Differentiation between splenomegaly, as revealed by an increased spleen-to-liver ratio with a normal spleen-to-pericardium ratio, and sequestration, as revealed by an increased spleen-to-liver ratio of 2:1 to 4:1 over the entire study period or a spleen-to-pericardium ratio of more than 2:170
  • Provision of guidance for treatment (splenectomy) that removes the source of RBC destruction, resulting in a prolonged RBC survival

Contraindications

• Pregnancy, unless the benefits of performing the study greatly outweigh the risks to the fetus
• Excessive bleeding or clotting abnormality

[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) and any nuclear laboratory study (see section under "Brain Scanning").

• Instruct the client in collection and testing of a stool specimen for occult blood if this part of the test is ordered.
• History should include a hematologic system assessment, vital signs, and results of hemoglobin, hematocrit, platelet, WBC, and reticulocyte counts.

Phase 1. A blood specimen of 10 mL is drawn from the client and centrifuged to remove the plasma. The remaining cells are labeled and reinjected. A blood sample is drawn 24 hours after the injection and then every other day for 3 weeks. Each specimen is analyzed for counts per minute of the radionuclide and plotted on graph paper to determine the RBC survival half-time. The rate at which the labeled cells disappear during the timed testing indicates the progression of cell destruction.

Phase 2. Scanning of the spleen, liver, and pericardium is performed on the same schedule as for phase 1 in conjunction with the RBC survival study. Splenic sequestration is determined by the concentration of the radionuclide at the site of cell damage. To determine splenic abnormalities, counts are performed for each area and spleen-to-liver and spleen-to-pericardium ratios are established.

Nursing Care After the Procedure

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

If scanning is performed, care and assessment are the same as for any nuclear scan study (see section under "Brain Scanning").

• Monitor vital signs and compare them with pretest readings.
• Monitor ordered replacement therapy in severe anemic state (packed RBC, IV fluids).
• Assess for fatigue or activity intolerance when RBC survival is decreasing, and provide rest and measures to preserve energy.
• Assess for jaundice, adequate hydration, and pain in anemic state when RBC survival is decreasing.
• Assess for hypoxic states when RBC survival rate is increasing and provide oxygen, if needed.
• Assess for ability to follow instructions for return to the laboratory for blood tests and scanning. Provide a written schedule.
• Provide support when diagnostic findings are revealed, especially if a congenital or chronic disorder is diagnosed, and assist in coping with the chronicity or life-threatening risk associated with an increase or decrease in RBC survival rate.