Tc-99m RBC Labelling

Question 1

what are the three protocols for RBC labelling with Tc-99m?

Answer 1

1. in vivo
2. modified in vivo
3. in vitro

Question 2

what is the general mechanism of RBC labelling?

Answer 2

1. stannous ion diffuses into RBC
2. free pert. diffuses into RBC
3. Sn2+ reduces free pert.
4. reduced Tc binds to hemoglobin and becomes “trapped” in the cell

Question 3

what is the difference between in vivo and in vitro?

Answer 3

it describes whether the stannous ion and/or pertechnetate is delivered to the RBC inside or outside of the body

Question 4

what is the procedure for in vivo labelling of RBC?

Answer 4

1. inject patient (IV) with cold stannous pyrophosphate
2. wait ~20 minutes for the RBC to “tin”
3. inject free pert., which then labels the “tinned” red cells

Question 5

during the in vivo method of labelling RBC, the amount of cold stannous pyrophosphate is dependent on _____. what is the typical range?

Answer 5

dependent on patient’s weight
10-20 ug/kg

Question 6

during the in vivo method of labelling RBC, what is the percentage of the yielded rbc that are labelled? why?

Answer 6

80-90%
because the red cells are competing with the normal biorouting of pertechn.

Question 7

what is the procedure for modified in vivo labelling of RBC?

Answer 7

1. inject patient with cold stannous pyrophosphate
2. wait ~20 minutes for red cells to tin
3. take 3ml of blood from patient
4. add the free pert. to blood
5. incubate with gentle agitation for ~10 minutes
6. reinject the blood into patient (with the labelled red cells)

Question 8

during the modified in vivo method of labelling RBC, what is the percentage of the yielded rbc that are labelled?

Answer 8

> 90%

Question 9

which method of labelling RBC uses Ultratag?

Answer 9

in vitro

Question 10

what is the labelling yield for the in vitro method?

Answer 10

> 95%

Question 11

what is contained in syringe I in the in vitro kit?

Answer 11

sodium hypochlorite with the pH of 11-13

Question 12

what is contained in syringe II in the in vitro kit?

Answer 12

citric acid, sodium citrate, and dextrose with the pH of 4.5-5.5

Question 13

what is the steps for the in vitro procedure to label RBC?

Answer 13

1. take 1-3 ml blood from patient
2. transfer blood into the reaction vial and incubate for 5 minutes
3. add contents of syringe I and mix
4. add contents of syringe II and mix
5. add free pert. and mix (max vol. of 3ml)
6. incubate for 20 minutes
7. reinject patient

Question 14

what is typically used as an anticoagulant during the in vitro method?

Answer 14

ACD or heparin

Question 15

describe what is occurring during the in vitro process.

Answer 15

• when blood is added, the stannous ion will diffuse into the rbc
• the sodium hypochlorite (syringe I) will oxidize any extracellular stannous ions
• citrate solution (syringe II) enhances the process by isolating any remaining extracellular stannous ions for oxidation by sodium hypochlorite
• pert added and it diffuses into the rbc to get reduced by the stannous ion and it will bind to the hemoglobin

Question 16

ACD dose should not exceed _____ of ACD per ml of blood.

Answer 16

0.15 ml of ACD per ml of blood

Question 17

what does the labelling efficiency of rbc’s signify?

Answer 17

the % of activity in the rbc in comparison to the activity of the whole blood

Question 18

what are the pros of in vivo?

Answer 18

cheap, easy, convenient + quick, no blood manipulation

Question 19

what are the pros of modified in vivo?

Answer 19

best of both in vivo and in vitro

Question 20

what are the pros of in vitro?

Answer 20

highest efficiency, best T:NT, precise

Question 21

which method is best for emergency procedures?

Answer 21

in vitro