In vivo / in vitro Method
(in vivtro Method)

1. 1 mg of Sn²⁺ in the form of pyrophosphate (“cold PYP”) is given IV

2. 20 min wait  to permit mixing of the Sn PYP in body and diffusion of Sn²⁺ into RBC.

3. Withdrawal of 5-10 ml of blood anti-coagulated with heparin or ACD solution into a syringe containing 25 mCi Tc-99m pertechnetate

4. 10 min waiting period to permit diffusion of the pertechnetate into RBCs and to permit labeling to reach equilibrium.

5. Reinjection of labeled cells into patient.

6. Expected labeling efficiency: ~92%

In vivo / in vitro: Advantages / disadvantages

  Advantages: quick, simple, inexpensive method; achieves higher labeling efficiency than in vivo/in vivo technique since incubation with RBC is extracorporeal. Not optimal for GI Bleeding Studies.

  Disadvantages: takes extra tech time; potential for breaking sterility

Modified In vivo / in vitro method

  1. 1 mg of Sn²⁺ in the form of pyrophosphate (“cold PYP”) is given IV.

  2.  20 min wait to permit mixing of the Sn PYP in body and diffusion of Sn²⁺ into RBC.

  3. Withdrawal of 5-10 ml of anti-coagulated blood (heparin, ACD) into vacutainer.

  4. Centrifuge the vacutainer in inverted position for 5 min at 3000 rpm.

  5.  Removal of 2-3 ml of packed cells through a 20 gauge or larger needle.

6.  Aseptic addition of these tinned, packed cells to a sterile vial containing 35 mCi of Tc-99m pertechnetate.

7. 10 min incubation to permit labeling reaction to go to completion. Expected labeling efficiency: 98-100%

8.  Reinjection of Tc RBC

Modified In vivo / in vitro Method Advantages/Disadvantages

  Advantages: quick, simple, inexpensive method; achieves highest labeling efficiency of all procedures since reaction of Tc with plasma proteins has been eliminated. Ideally suited for GI Bleeding Studies; produces excellent delayed images.

  Disadvantage: Takes extra tech time; requires clinical centrifuge; potential for breaking sterility.