THE FOLLOWING PROCEDURES ARE COPIES FROM MALLINCKRODT'S PACKAGE INSERT:

 ⁵¹Cr FOR RED CELL VOLUME ANALYSIS

PROCEDURE:

Refer to the Power Point Presentation for additional visuals on this procedure.

1. With A-C-D solution from the A-C-D tagging vial, wet a 20-ml syringe and then use the syringe to withdraw 15 ml of blood from the patient's antecubital vein.   (Gauge size should be at least 19)
2. Slowly and gently (to prevent hemolysis) aseptically inject the contents of the syringe into the vial of A-C-D solution.
3. Aseptically add approximately (100 :Ci) of Sodium Chromate 51Cr to the A-C-D mixture.
4. Gently mix the blood by intermittent swirling every 5 to 10 minutes.   Allow to tag at room temperature for 30 minutes.
5. After 30 minutes of mixing aseptically add 30 to 50 mg of ascorbic acid to the A-C-D vial, mix gently, and allow to stand for 5 minutes.
6. After gently mixing, withdraw exactly 10 ml of the tagged red blood cell (RBC) suspension, and inject intravenously into the patient.
7. Determine the hematocrit of the remaining Tagged RBC Suspension Hct 1
8. Pipet 1 ml of the tagged RBC suspension into a 100-ml volumetric flask and dilute to 100 ml with water.   Mix thoroughly and pipet 4 ml into a counting vial.   This is the Whole Blood Standard WB 1
9. Centrifuge the remaining tagged RBC suspension, and pipet 1 ml of the plasma into a 100-ml volumetric flask, and dilute to 100 ml with water.   Mix thoroughly, and pipet 4 ml into a counting vial.   This is the Plasma Standard Pl 1
10. Ten to twenty minutes after injecting the patient withdraw approximately 20 ml of blood with a sterile, evacuated container containing an anticoagulant.
11. Pipet 4 ml of the whole blood into a counting vial.   This is the Patient Whole Blood Sample WB 2
12. Remove a sample for a Patient Hematocrit HCT 2 and centrifuge the remaining blood.
13. Pipet 4 ml of plasma into a counting vial.   This is the Patient Plasma Sample Pl 2.
14. Count the follow for 20 minutes each:
    1. Whole Blood Standard WB
    2. Plasma Standard Pl 1
    3. Patient Whole Blood Sample WB 2
    4. Patient Plasma Sample Pl 2
    5. Background
15. Subtract background from the above 4 counting vials.  Counting times should be equal and of sufficient length to provide a minimum of 10,000 counts.

CALCULATIONS:

• Hct 1 =   Hematocrit of Tagged RBC Suspension [A-C-D vial]
• WB 1 =   Net Whole Blood Standard Count
• P1 1 =   Net Plasma Standard Count
• WB 2 =   Net Patient Whole Blood Sample Count
• Hct 2 =   Patient Hematocrit (step 12)
•  P1 2 =   Net Patient Plasma Sample Count

1. A-C-D vial comes in a solution and is an anticoagulant.   You do not want the blood to clot, hence use of this solution is essential.
2. Do not inject and withdraw the patient’s blood from the same injection site.   This could add additional activity in the patient’s sample which would elevate count rate in the sample.   Falsely affecting the exam.
3. Follow the procedure like a cookbook, any deviation may or will cause error!
4. Always acquire enough counts!   Remember at least 10,000 counts are required to significantly reduce statistical error.
5. Issue – Why does the standard have to be diluted?
   1. Failure to dilute the standard means that you would be counting numerous μCi amounts of ⁵¹Cr in the standard. The well counter can handle no more than 1 μCi.   Any additional amount of activity would cause an increase in dead time reduced count rate from the sample.
6. Issue – Use the correct Hct in the formula (1 and 2).
   1. You’re A-C-D vial has a diluted Hct level since this solution is present prior to adding the patient’s blood.   Hct 1 comes from you’re A-C-D vial and Hct 2 is the patient’s hematocrit.
7. Issue – Can you blend RISA (Plasma Volume) with the Red Cell Volume exam?
   1. Yes – However, you must first do the RISA test and then the Red Cell Volume test.   Reason:   ¹²⁵I RISA has a lower keV gamma when compared to ⁵¹Cr.   Therefore, ¹²⁵I will not interfere with the counts in the ⁵¹Cr window.   However, if ⁵¹Cr is added first, then Compton scatter counts will spill into ¹²⁵I window.  
8. This procedure describes Red Cell Volume, however, Red Cell Mass is another value you must obtain.   Refer to the formulas above.   Note the Red Cell Mass is obtained by taking the Red Cell Volume and dividing by the patient weight (kg).

The following formulas should be applied for different blood volume determinations:

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