In Vivo Non Imaging Procedures:

Red Blood Cell Survival

PROCEDURE

• Radiopharmaceutical: Cr-51 RBCs, 50-75 mCi
   
• Useful in evaluating patients with anemia of unknown etiology when a hemolytic process is suspected
   
• 28-35 days is considered normal half time of survival  for Cr-51 labeled autologous RBC's.
   
• AUTOLOGOUS RED CELL LABELING:  20 ml citrated whole blood, 15 min incubation at room temperature using Cr-51  Na chromate
   
• BLOOD SAMPLING: on a daily basis through day 10
   
• DATA ANALYSIS: semilogarithmic graphical analysis of change in count rate as f (time)
  
   

  
  
  
   

• EXPECTED LIFETIME OF RED CELLS IN THE BLOOD POOL: Since it has been well documented that red cells live approximately 120 days, it might seem logical that the half-time of survival of red cells would be 60 days. However, in a randomly drawn blood sample, the cells are all different ages (0-120 days) at time of incorporation of radioisotope; therefore, the average age of the population of all cells is 60 days and the half-time of survival of this population would therefore be 30 days.
   

LIMITATIONS

• If cells are damaged during the radiolabeling procedure, artificially shortened survival time may result
   
• Procedure is very time-consuming, since patient must return and be counted for up to 14 days;
   
• Blood loss, e.g., GI tract, urinary tract, or surgery may falsely shorten survival time.