Ultratag RBC

ULTRATAG RBC- technetium tc 99m-labeled red blood cells
Curium US LLC

DESCRIPTION

Ultratag™ RBC (kit for the preparation of technetium Tc 99m-labeled red blood cells) is a sterile, nonpyrogenic, diagnostic kit for the in vitro preparation of technetium Tc 99m-labeled red blood cells.

Each kit consists of three separate nonradioactive components:

  1. A 10 milliliter reaction vial containing:
    Stannous Chloride, Dihydrate (SnCl2 •2H2 O) – 50 ug minimum
    Stannous Chloride, Dihydrate (SnCl2 •2H2 O) – 96 ug theoretical
    Tin Chloride (Stannous and Stannic), Dihydrate (as SnCl2 •2H2 O) – 105 ug maximum
    Sodium Citrate, Dihydrate – 3.67 mg
    Dextrose, Anhydrous – 5.50 mg
    Prior to lyophilization, the pH is adjusted to 7.1 to 7.2 with sodium hydroxide. The contents of the vial are lyophilized and stored under argon.
  2. Syringe I contains:
    Sodium Hypochlorite – 0.6 mg in Sterile Water for InjectionThe total volume of this syringe is 0.6 mL. Sodium hydroxide may have been added for pH adjustment. The pH of this solution is 11 to 13. The syringe must be protected from light to prevent degradation of the light-sensitive sodium hypochlorite.
  3. Syringe II contains:
    Citric Acid, Monohydrate – 8.7 mg
    Sodium Citrate, Dihydrate – 32.5 mgDextrose, Anhydrous – 12.0 mg in Sterile Water for Injection

The total volume of this syringe is 1.0 mL. The pH range of this solution is adjusted to 4.5 to 5.5 with sodium citrate or citric acid.

PHYSICAL CHARACTERISTICS

Technetium Tc 99m decays by isomeric transition with a physical half-life of 6.02 hours.1 The principal photon that is useful for detection and imaging is listed in Table 1.

Table 1. Principal Radiation Emission Data *
*
Kocher, David C., “Radioactive Decay Tables,” DOE/TIC 11026, 108 (1981).
Radiation Mean % /Disintegration Energy (keV)
Gamma-2 89.07 140.5

The specific gamma ray constant for technetium Tc 99m is 0.78 R/mCi-hr at 1 cm. The first half-value thickness of lead (Pb) for technetium Tc 99m is 0.017 cm. A range of values for the relative attenuation of the radiation emitted by this radionuclide resulting from the interposition of various thicknesses of lead (Pb) is presented in Table 2. For example, the use of 0.25 cm of lead will decrease the external radiation exposure by a factor of about 1000.

Table 2. Radiation Attenuation by Lead Shielding
Shield Thickness (Pb) cm Coefficient ofAttenuation
0.017 0.5
0.08 10-1
0.16 10-2
0.25 10-3
0.33 10-4

To correct for physical decay of this radionuclide, the fractions that remain at selected intervals after the time of calibration are presented in Table 3.

Table 3. Physical Decay Chart: Technetium Tc 99m, Half-Life: 6.02 Hours

*Calibration Time

Hours FractionRemaining Hours FractionRemaining
0* 1.000 7 0.447
1 0.891 8 0.398
2 0.794 9 0.355
3 0.708 10 0.316
4 0.631 11 0.282
5 0.562 12 0.251
6 0.501

CLINICAL PHARMACOLOGY

In vitro Tc 99m red blood cell labeling is accomplished by adding 1.0 to 3.0 milliliters of autologous whole blood, anticoagulated with heparin or Anticoagulant Citrate Dextrose Solution (ACD), to the reaction vial. A portion of the stannous ion in the reaction vial diffuses across the red blood cell membrane and accumulates intracellularly. The in vitro Tc 99m red blood cell labeling efficiency can decrease in the presence of excess ACD. Excess ACD apparently impairs the diffusion of stannous ion across the red blood cell membrane. Therefore, the ACD concentration used for blood collection should not exceed 0.15 mL ACD per mL of blood. Sodium hypochlorite is then added to the reaction vial to oxidize the extracellular stannous ion. Since the hypochlorite does not cross the red blood cell membrane, the oxidation of stannous ion is selective for the extracellular tin. A citric acid, sodium citrate and dextrose solution is then added to the reaction vial to sequester any residual extracellular stannous ion, rendering it more readily available for oxidation by sodium hypochlorite.
Radioactive labeling of the red blood cells is completed by addition of sodium pertechnetate Tc 99m to the oxidized reaction vial. The pertechnetate Tc 99m diffuses across the red blood cell membrane and is reduced by the intracellular stannous ion. The reduced technetium Tc 99m cannot diffuse out of the red blood cell. The red blood cell labeling is essentially complete within 20 minutes of sodium pertechnetate Tc 99m addition to the reaction vial. Red blood cell labeling efficiency of ≥95% is typically obtained using this in vitro labeling procedure. In vitro Tc 99m red blood cell labeling efficiency can decrease when excessive amounts of Tc 99 are allowed to accumulate in the sodium pertechnetate Tc 99m generator eluate; in this situation, efficiency decreases even further if excess (i.e. >0.15 mL per mL of blood) ACD buffer is used. Therefore, long Tc 99 in-growth times are to be avoided; the use of fresh (≤24 hour in-growth time) sodium pertechnetate Tc 99m generator eluate is recommended. After the labeling procedure is completed, the technetium Tc 99m-labeled red blood cells are then reinjected intravenously into the patient for gamma scintigraphic imaging.
Following intravenous injection, the technetium Tc 99m-labeled red blood cells distribute within the blood pool with an estimated volume of distribution of approximately 5.6% of bodyweight. The technetium Tc 99m is well retained in the blood pool with an estimated biological half-life of approximately 29 hours. Of the total technetium Tc 99m retained in the whole blood pool 24 hours after administration, 95% remains bound to the red blood cells. Approximately 25% of the injected dose is excreted in the urine in the first 24 hours.

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