Scintigraphy performed with Tc-99m labeled RBCs

Last revised by Mostafa Elfeky on 15 Oct 2023

Tc-99m labeled RBCs - with radiolabelling technique in vivo or in vitro of red cells 3 - is one of the technetium radiopharmaceuticals used in the non-invasive assessment of gastrointestinal (GI) bleeding 2, characterized by high sensitivity (93%) and specificity (95%) 4. It is capable, in fact, of targeting intestinal hemorrhages of a few milliliters immediately after the injection of the radioactive tracer or in the following 12-24 hours (diluition principle) 5,6.

There are three ways to label erythrocytes, namely in vivo, modified in vivo, and in vitro methods. In vivo method injects stannous pyrophosphate into the patient's blood, followed by Tc99m-pertechnetate injection. However, this method has low labeling efficiency. In the modified in vivo method, the blood is withdrawn after injecting the stannous pyrophosphate. The blood is then withdrawn from the patient mixed with Tc-99m-pertechnetate and injected back into the same patient. In the in vitro method, the blood is first withdrawn from the patient and mixed with stannous pyrophosphate and Tc-99m-pertechnetate using a cold kit. After mixing, the blood is then injected back into the patient. This method has the highest labeling efficiency 7.

Stannous pyrophosphate is important because it acts as a reducing agent in order to prevent pertechnetate ions from diffusing into the extravascular spaces, affecting the labeling efficacy of the RBCs 8.


  • photon energy: 140 KeV

  • physical half-life: 6 hours

  • biological half-life: 

  • normal distribution: heart, vessels, spleen

  • miscellaneous facts:

    • threshold for detection is 0.05-0.1 mL/min

    • angiography threshold is 0.5-1 mL/min

    • the criteria for positive scan are qualitative type: hot spot appears and conforms to intestinal anatomy, abnormal activity increases over time, activity moves antegrade or retrograde through bowel

Uses, doses and timings

  • GI bleeding

  • adult dose: 925 MBq (25 mCi) IV

  • timing: immediate/angioscintigraphic phase (1 sec frames x 60 sec); 1 min frames x 60-90 min; delayed imaging if necessary (6-8-24 hrs).

ADVERTISEMENT: Supporters see fewer/no ads