9613
Because there is great need for iron in the EPO - stimulated erythroid progenitors , it is essential that serum ferritin and transferrin saturation levels should be maintained over 300 microg / liter and 30 % , respectively .
 EPO, serum ferritin, transferrin
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 EPO, serum ferritin, transferrin